LM3409EVAL/NOPB - NATIONAL SEMICONDUCTOR

LM3409

LM3409HV

June 12, 2009

PFET Buck Controller for High Power LED Drives

General Description

The LM3409/09HV are P-channel MosFET (PFET) con-

trollers for step-down (buck) current regulators. They offer

wide input voltage range, high-side differential current sense

with low adjustable threshold voltage, fast output enable/dis-

able function and a thermally enhanced eMSOP-10 package.

These features combine to make the LM3409/09HV ideal for

use as constant current sources for driving LEDs where for-

ward currents up to 5A are easily achievable. The

LM3409/09HV uses Constant Off-Time (COFT) control to

regulate an accurate constant current without the need for

external control loop compensation. Analog and PWM dim-

ming are easy to implement and result in a highly linear

dimming range with excellent achievable contrast ratios. Pro-

grammable UVLO, low-power shutdown, and thermal shut-

down complete the feature set.

Features

■2Ω, 1A Peak MosFET Gate Drive

■VIN Range: 6V to 42V (LM3409)

■VIN Range: 6V to 75V (LM3409HV)

■Differential, High-side Current Sense

■Cycle-by-Cycle Current Limit

■No Control Loop Compensation Required

■10,000:1 PWM Dimming Range

■250:1 Analog Dimming Range

■Supports All-Ceramic Output Capacitors and Capacitor-

less Outputs

■Low Power Shutdown

■Thermal Shutdown Protection

■Thermally Enhanced eMSOP-10 Package

Applications

■LED Driver

■Constant Current Source

■Automotive Lighting

■General Illumination

■Industrial Lighting

Typical Application

30085601

LM3409 / LM3409HV PFET Buck Controller for High Power LED Drives

Connection Diagram

LM3409/09HV

30085602

10-Lead Exposed Pad eMSOP Package

Ordering Information

Order Number NSC Package Drawing Top Marking Supplied As

LM3409MY MUC10A SXFB 1000 Units on tape and reel

LM3409MYX MUC10A SXFB 3500 Units on tape and reel

LM3409HVMY MUC10A SYHB 1000 Units on tape and reel

LM3409HVMYX MUC10A SYHB 3500 Units on tape and reel

Pin Descriptions

Pin(s) Name Description Application Information

1 UVLO Input under-voltage lockout Connect to a resistor divider from VIN and GND. Turn-on threshold is

1.24V and hysteresis for turn-off is provided by a 22µA current source.

2 IADJ Analog LED current adjust Apply a voltage between 0 - 1.24V, connect a resistor to GND, or leave

open to set the current sense threshold voltage.

3 EN Logic level enable /

PWM dimming

Apply a voltage >1.74V to enable device, a PWM signal to dim, or a

voltage <0.5V for low power shutdown.

4 COFF Off-time programming Connect a resistor from VO, and a capacitor from GND to set the off-

time.

5 GND Ground Connect to the system ground.

6 PGATE Gate drive Connect to the gate of the external PFET.

7 CSN Negative current sense Connect to the negative side of the sense resistor.

8 CSP Positive current sense Connect to the positive side of the sense resistor (also connected to

VIN).

9 VCC VIN- referenced

linear regulator output

Connect at least a 1µF ceramic capacitor to VIN. The regulator provides

power for the PFET drive.

10 VIN Input voltage Connect to the input voltage.

DAP DAP Thermal pad on bottom of IC Connect to pin 5 (GND). Place 4-6 vias from DAP to bottom layer GND

plane.

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LM3409/LM3409HV

Absolute Maximum Ratings

LM3409/09HV (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VIN, EN, UVLO to GND -0.3V to 45V

(76V LM3409HV)

VIN to VCC, PGATE -0.3V to 7V

VIN to PGATE -2.8V for 100ns

9.5V for 100ns

VIN to CSP, CSN -0.3V to 0.3V

COFF to GND -0.3V to 4V

COFF current ±1 mA continuous

IADJ Current ±5 mA continuous

Junction Temperature 150°C

Storage Temp. Range -65°C to 125°C

ESD Rating (Note 2) 1kV

Soldering Information

Lead Temperature (Soldering,

10sec) 260°C

Infrared/Convection Reflow (15sec) 260°C

Operating Ratings (LM3409/09HV)

(Note 1)

VIN 6V to 42V

(75V LM3409HV)

Junction Temperature Range −40°C to +125°C

Thermal Resistance θJA

(eMSOP-10 Package)

(Note 5) 50°C/W

Electrical Characteristics VIN = 24V unless otherwise indicated. Typicals and limits appearing in plain type apply

for TA = TJ = +25°C (Note 3). Limits appearing in boldface type apply over full Operating Temperature Range. Datasheet min/

max specification limits are guaranteed by design, test, or statistical analysis.

LM3409/LM3409HV

Symbol Parameter Conditions Min

(Note 4)

Typ

(Note 3)

Max

(Note 4)

Units

PEAK CURRENT COMPARATOR

VCST VCSP – VCSN average peak

current threshold

(Note 6)

VADJ = 1.0V 188 198 208 mV

VADJ = VADJ-OC 231 246 261

AADJ VADJ to VCSP – VCSN threshold

gain

0.1 < VADJ < 1.2V

VADJ = VADJ-OC

0.2 V/V

VADJ-OC IADJ pin open circuit voltage 1.189 1.243 1.297 V

IADJ IADJ pin current 3.8 56.4 µA

tDEL CSN pin falling delay CSN fall - PGATE rise 38 ns

SYSTEM CURRENTS

IIN Operating current Not switching 2 mA

ISD Shutdown hysteresis current EN = 0V 110 µA

PFET DRIVER

RPGATE Driver output resistance Sourcing 50 mA 2 Ω

Sinking 50 mA 2

VCC REGULATOR

VCC VIN pin voltage - VCC pin

voltage

VIN > 9V

0 < ICC < 20 mA

5.5 66.5 V

VCC-UVLO VCC under voltage lockout

threshold

VCC increasing 3.73 V

VCC-HYS VCC UVLO hysteresis VCC decreasing 283 mV

ICC-LIM VCC regulator current limit 30 45 mA

OFF-TIMER AND ON-TIMER

VOFT Off-time threshold 1.122 1.243 1.364 V

tD-OFF COFF threshold to PGATE

falling delay

25 ns

tON-MIN Minimum on-time 115 211 ns

tOFF-MAX Maximum off-time 300 µs

UNDER VOLTAGE LOCKOUT

IUVLO UVLO pin current VUVLO = 1V 10 nA

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LM3409/LM3409HV

Symbol Parameter Conditions Min

(Note 4)

Typ

(Note 3)

Max

(Note 4)

Units

VUVLO-R Rising UVLO threshold 1.175 1.243 1.311 V

IUVLO-HYS UVLO hysteresis current 22 µA

ENABLE

IEN EN pin current 10 nA

VEN-TH EN pin threshold VEN rising 1.74 V

VEN falling .5

VEN-HYS EN pin hysteresis 420 mV

tEN-R EN pin rising delay EN rise - PGATE fall 42 ns

tEN-F EN pin falling delay EN fall - PGATE rise 21 ns

THERMAL RESISTANCE

θJA Junction to Ambient eMSOP-10 Package (Note 5) 50 °C/W

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability

and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in

the Operating Ratings is not implied. The recommended Operating Ratings indicate conditions at which the device is functional and the device should not be

operated beyond such conditions.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: Typical values represent most likely parametric norms at the conditions specified and are not guaranteed.

Note 4: Min and Max limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical

Quality Control (SQC) methods. Limits are used to calculate National's Average Outgoing Quality Level (AOQL).

Note 5: θJA of 50°C/W with DAP soldered to a minimum of 2 square inches of 1oz. copper on the top or bottom PCB layer. Actual value will be different depending

upon the application enviroment.

Note 6: The current sense threshold limits are calculated by averaging the results from the two polarities of the high-side differential amplifier.

Note 7: The measurements were made using the Bill of Materials from Design #3.

Note 8: The measurements were made using the Bill of Materials from Design #3 except the LM3409 was substituted for the LM3409HV.

Note 9: The waveforms were acquired using the standard evaluation board from AN-1953.

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LM3409/LM3409HV

Typical Performance Characteristics

TA = +25°C, VIN = 24V, and characteristics are identical for LM3409 and LM3409HV unless otherwise specified.

VCST vs. Junction Temperature

300856b5

VCC vs. Junction Temperature

300856b6

VADJ vs. Junction Temperature

300856b8

IADJ vs. Junction Temperature

300856b7

VOFT vs. Junction Temperature

300856b9

tON-MIN vs. Junction Temperature

300856c0

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LM3409/LM3409HV

LM3409 Efficiency vs. Input Voltage

VO = 17V (5 LEDs); ILED = 2A (Note 8)

300856f0

LM3409HV Efficiency vs. Input Voltage

VO = 17V (5 LEDs); ILED = 2A (Note 7)

300856b3

LM3409 LED Current vs. Input Voltage

VO = 17V (5 LEDs) (Note 8)

300856f1

LM3409HV LED Current vs. Input Voltage

VO = 17V (5 LEDs) (Note 7)

300856b4

Normalized Switching Frequency

vs. Input Voltage

300856c1

Amplitude Dimming Using IADJ Pin

VO = 17V (5 LEDs); VIN = 24V

300856b2

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LM3409/LM3409HV

Internal EN Pin PWM Dimming

VO = 17V (5 LEDs); VIN = 24V

300856b0

External Parallel FET PWM Dimming

VO = 17V (5 LEDs); VIN = 24V

300856b1

20kHz 50% EN pin PWM dimming

VO = 42V (12 LEDs); VIN = 48V (Note 9)

300856f5

100kHz 50% External FET PWM dimming

VO = 42V (12 LEDs); VIN = 48V (Note 9)

300856f6

20kHz 50% EN pin PWM dimming (rising edge)

VO = 42V (12 LEDs); VIN = 48V (Note 9)

300856f7

100kHz 50% External FET PWM dimming (rising edge)

VO = 42V (12 LEDs); VIN = 48V (Note 9)

300856f8

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LM3409/LM3409HV

Block Diagram

30085603

Theory of Operation

The LM3409/09HV are P-channel MosFET (PFET) con-

trollers for step-down (buck) current regulators which are

ideal for driving LED loads. They have wide input voltage

range allowing for regulation of a variety of LED loads. The

high-side differential current sense, with low adjustable

threshold voltage, provides an excellent method for regulating

output current while maintaining high system efficiency. The

LM3409/09HV uses a Controlled Off-Time (COFT) architec-

ture that allows the converter to be operated in both continu-

ous conduction mode (CCM) and discontinuous conduction

mode (DCM) with no external control loop compensation,

while providing an inherent cycle-by-cycle current limit. The

adjustable current sense threshold provides the capability to

amplitude (analog) dim the LED current over the full range

and the fast output enable/disable function allows for high

frequency PWM dimming using no external components.

When designing, the maximum attainable LED current is not

internally limited because the LM3409/09HV is a controller.

Instead it is a function of the system operating point, compo-

nent choices, and switching frequency allowing the

LM3409/09HV to easily provide constant currents up to 5A.

This simple controller contains all the features necessary to

implement a high efficiency versatile LED driver.

BUCK CURRENT REGULATORS

The buck regulator is unique among non-isolated topologies

due to the direct connection of the inductor to the load during

the entire switching cycle. An inductor will control the rate of

change of current that flows through it, therefore a direct con-

nection to the load is excellent for current regulation. A buck

current regulator, using the LM3409/09HV, is shown in the

Typical Application section on the first page of this datasheet.

During the time that the PFET (Q1) is turned on (tON), the input

voltage charges up the inductor (L1). When Q1 is turned off

(tOFF), the re-circulating diode (D1) becomes forward biased

and L1 discharges. During both intervals, the current is sup-

plied to the load keeping the LEDs forward biased. Figure 1

shows the inductor current (iL(t)) waveform for a buck con-

verter operating in CCM.

The average inductor current (IL) is equal to the average out-

put LED current (ILED), therefore if IL is tightly controlled, ILED

will be well regulated. As the system changes input voltage

or output voltage, duty cycle (D) is varied to regulate IL and

ultimately ILED. For any buck regulator, D is simply the con-

version ratio divided by the efficiency (η):

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LM3409/LM3409HV

30085604

FIGURE 1. Ideal CCM Buck Converter Inductor Current iL(t)

CONTROLLED OFF-TIME (COFT) ARCHITECTURE

The COFT architecture is used by the LM3409/09HV to con-

trol ILED. It is a combination of peak current detection and a

one-shot off-timer that varies with output voltage. D is indi-

rectly controlled by changes in both tOFF and tON, which vary

depending on the operating point. This creates a variable

switching frequency over the entire operating range. This type

of hysteretic control eliminates the need for control loop com-

pensation necessary in many switching regulators, simplify-

ing the design process and providing fast transient response.

Adjustable Peak Current Control

At the beginning of a switching period, PFET Q1 is turned on

and inductor current increases. Once peak current is detect-

ed, Q1 is turned off, the diode D1 forward biases, and inductor

current decreases. Figure 2 shows how peak current detec-

tion is accomplished using the differential voltage signal cre-

ated as current flows through the current setting resistor

(RSNS). The voltage across RSNS (VSNS) is compared to the

adjustable current sense threshold (VCST) and Q1 is turned

off when VSNS exceeds VCST, providing that tON is greater than

the minimum possible tON (typically 115ns).

30085605

FIGURE 2. Peak Current Control Circuit

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LM3409/LM3409HV

There are three different methods to set the current sense

threshold (VCST) using the multi-function IADJ pin:

1. IADJ pin left open: 5µA internal current source biases the

Zener diode and clamps the IADJ pin voltage (VADJ) at

1.24V causing the maximum threshold voltage:

2. External voltage (VADJ) of 0V to 1.24V: Apply to the IADJ

pin to adjust VCST from 0V to 248mV. If the VADJ voltage

is adjustable, analog dimming can be achieved.

3. External resistor (REXT) placed from IADJ pin to ground:

5µA current source sets the VADJ voltage and

corresponding threshold voltage:

Controlled Off-Time

Once Q1 is turned off, it remains off for a constant time

(tOFF) which is preset by an external resistor (ROFF), an ex-

ternal capacitor (COFF), and the output voltage (VO) as shown

in Figure 3. Since ILED is tightly regulated, VO will remain

nearly constant over widely varying input voltage and tem-

perature yielding a nearly constant tOFF.

30085606

FIGURE 3. Off-Time Control Circuit

At the start of tOFF, the voltage across COFF (vCOFF(t)) is zero

and the capacitor begins charging according to the time con-

stant provided by ROFF and COFF. When vCOFF(t) reaches the

off-time threshold (VOFT = 1.24V), then the off-time is termi-

nated and vCOFF(t) is reset to zero. tOFF is calculated as

follows:

In reality, there is typically 20 pF parasitic capacitance at the

off-timer pin in parallel with COFF, which is accounted for in

the calculation of tOFF. Also, it should be noted that the tOFF

equation has a preceding negative sign because the result of

the logarithm should be negative for a properly designed cir-

cuit. The resulting tOFF is a positive value as long as VO >

1.24V. If VO < 1.24V, the off-timer cannot reach VOFT and an

internally limited maximum off-time (typically 300µs) will oc-

cur.

30085607

FIGURE 4. Exponential Charging Function vCOFF(t)

Although the tOFF equation is non-linear, tOFF is actually very

linear in most applications. Ignoring the 20pF parasitic ca-

pacitance at the COFF pin, vCOFF(t) is plotted in Figure 4. The

time derivative of vCOFF(t) can be calculated to find a linear

approximation to the tOFF equation:

When tOFF << ROFF x COFF (equivalent to when VO >> 1.24V),

the slope of the function is essentially linear and tOFF can be

approximated as a current source charging COFF:

Using the actual tOFF equation, the inductor current ripple

(ΔiL-PP) of a buck current regulator operating in CCM is:

Using the tOFF approximation, the equation is reduced to:

ΔiL-PP is independent of both VIN and VO when in CCM!

The ΔiL-PP approximation only depends on ROFF, COFF, and

L1, therefore the ripple is essentially constant over the oper-

ating range as long as VO >> 1.24V (when the tOFF approxi-

mation is valid). An exception to the tOFF approximation

occurs if the IADJ pin is used to analog dim. As the LED/in-

ductor current decreases, the converter will eventually enter

DCM and the ripple will decrease with the peak current thresh-

old. The approximation shows how the LM3409/09HV

achieves constant ripple over a wide operating range, how-

ever tOFF should be calculated using the actual equation first

presented.

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LM3409/LM3409HV

AVERAGE LED CURRENT

For a buck converter, the average LED current is simply the

average inductor current.

30085611

FIGURE 5. Sense Voltage vSNS(t)

Using the COFT architecture, the peak transistor current (IT-

MAX) is sensed as shown in Figure 5, which is equal to the

peak inductor current (IL-MAX) given by the following equation:

Because IL-MAX is set using peak current control and ΔiL-PP is

set using the controlled off-timer, IL and correspondingly

ILED can be calculated as follows:

The threshold voltage VCST seen by the high-side sense com-

parator is affected by the comparator’s input offset voltage,

which causes an error in the calculation of IL-MAX and ulti-

mately ILED. To mitigate this problem, the polarity of the com-

parator inputs is swapped every cycle, which causes the

actual IL-MAX to alternate between two peak values (IL-MAXH

and IL-MAXL), equidistant from the theoretical IL-MAX as shown

in Figure 6. ILED remains accurate through this averaging.

30085612

FIGURE 6. Inductor Current iL(t) Showing IL-MAX Offset

INDUCTOR CURRENT RIPPLE

Because the LM3409/09HV swaps the polarity of the differ-

ential current sense comparator every cycle, a minimum in-

ductor current ripple (ΔiL-PP) is necessary to maintain

accurate ILED regulation. Referring to Figure 6, the first tON is

terminated at the higher of the two polarity-swapped thresh-

olds (corresponding to IL-MAXH). During the following tOFF, iL

decreases until the second tON begins. If tOFF is too short, then

as the second tON begins, iL will still be above the lower peak

current threshold (corresponding to IL-MAXL) and a minimum

tON pulse will follow. This will result in degraded ILED regula-

tion. The minimum inductor current ripple (ΔiL-PP-MIN) should

adhere to the following equation in order to ensure accurate

ILED regulation:

SWITCHING FREQUENCY

The switching frequency is dependent upon the actual oper-

ating point (VIN and VO). VO will remain relatively constant for

a given application, therefore the switching frequency will vary

with VIN (frequency increases as VIN increases). The target

switching frequency (fSW) at the nominal operating point is

selected based on the tradeoffs between efficiency (better at

low frequency) and solution size/cost (smaller at high fre-

quency). The off-time of the LM3409/09HV can be pro-

grammed for switching frequencies up to 5 MHz (theoretical

limit imposed by minimum tON). In practice, switching fre-

quencies higher than 1MHz may be difficult to obtain due to

gate drive limitations, high input voltage, and thermal consid-

erations.

At CCM operating points, fSW is defined as:

At DCM operating points, fSW is defined as:

In the CCM equation, it is apparent that the efficiency (η) fac-

tors into the switching frequency calculation. Efficiency is hard

to estimate and, since switching frequency varies with input

voltage, accuracy in setting the nominal switching frequency

is not critical. Therefore, a general rule of thumb for the

LM3409/09HV is to assume an efficiency between 85% and

100%. When approximating efficiency to target a nominal

switching frequency, the following condition must be met:

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LM3409/LM3409HV

30085614

FIGURE 7. LED Current iLED(t) During EN Pin PWM Dimming

PWM DIMMING USING THE EN PIN

The enable pin (EN) is a TTL compatible input for PWM dim-

ming of the LED. A logic low (below 0.5V) at EN will disable

the internal driver and shut off the current flow to the LED

array. While the EN pin is in a logic low state the support cir-

cuitry (driver, bandgap, VCC regulator) remains active in order

to minimize the time needed to turn the LED array back on

when the EN pin sees a logic high (above 1.74V).

Figure 7 shows the LED current (iLED(t)) during PWM dimming

where duty cycle (DDIM) is the percentage of the dimming pe-

riod (TDIM) that the PFET is switching. For the remainder of

TDIM, the PFET is disabled. The resulting dimmed average

LED current (IDIM-LED) is:

The LED current rise and fall times (which are limited by the

slew rate of the inductor as well as the delay from activation

of the EN pin to the response of the external PFET) limit the

achievable TDIM and DDIM. In general, dimming frequency

should be at least one order of magnitude lower than the

steady state switching frequency in order to prevent aliasing.

However, for good linear response across the entire dimming

range, the dimming frequency may need to be even lower.

HIGH VOLTAGE NEGATIVE BIAS REGULATOR

The LM3409/09HV contains an internal linear regulator where

the steady state VCC pin voltage is typically 6.2V below the

voltage at the VIN pin. The VCC pin should be bypassed to

the VIN pin with at least 1µF of ceramic capacitance connect-

ed as close as possible to the IC.

INPUT UNDER-VOLTAGE LOCKOUT (UVLO)

Under-voltage lockout is set with a resistor divider from VIN to

GND and is compared against a 1.24V threshold as shown in

Figure 8. Once the input voltage is above the preset UVLO

rising threshold (and assuming the part is enabled), the inter-

nal circuitry becomes active and a 22µA current source at the

UVLO pin is turned on. This extra current provides hysteresis

to create a lower UVLO falling threshold. The resistor divider

is chosen to set both the UVLO rising and falling thresholds.

30085613

FIGURE 8. UVLO Circuit

The turn-on threshold (VTURN-ON) is defined as follows:

The hysteresis (VHYS) is defined as follows:

LOW POWER SHUTDOWN

The LM3409/09HV can be placed into a low power shutdown

(typically 110µA) by grounding the EN terminal (any voltage

below 0.5V) until VCC drops below the VCC UVLO threshold

(typically 3.73V). During normal operation this terminal should

be tied to a voltage above 1.74V and below absolute maxi-

mum input voltage rating.

THERMAL SHUTDOWN

Internal thermal shutdown circuitry is provided to protect the

IC in the event that the maximum junction temperature is ex-

ceeded. The threshold for thermal shutdown is 160°C with 15°

C of hysteresis (both values typical). During thermal shut-

down the PFET and driver are disabled.

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LM3409/LM3409HV

Design Considerations

OPERATION NEAR DROPOUT

Because the power MosFET is a PFET, the LM3409/09HV

can be operated into dropout which occurs when the input

voltage is approximately equal to output voltage. Once the

input voltage drops below the nominal output voltage, the

switch remains constantly on (D=1) causing the output volt-

age to decrease with the input voltage. In normal operation,

the average LED current is regulated to the peak current

threshold minus half of the ripple. As the converter goes into

dropout, the LED current is exactly at the peak current thresh-

old because it is no longer switching. This causes the LED

current to increase by half of the set ripple current as it makes

the transition into dropout. Therefore, the inductor current rip-

ple should be kept as small as possible (while remaining

above the previously established minimum) and output ca-

pacitance should be added to help maintain good line regu-

lation when approaching dropout.

LED RIPPLE CURRENT

Selection of the ripple current through the LED array is anal-

ogous to the selection of output ripple voltage in a standard

voltage regulator. Where the output voltage ripple in a voltage

regulator is commonly ±1% to ±5% of the DC output voltage,

LED manufacturers generally recommend values for ΔiLED-

PP ranging from ±5% to ±20% of ILED. For a nominal system

operating point, a larger ΔiLED-PP specification can reduce the

necessary inductor size and/or allow for smaller output ca-

pacitors (or no output capacitors at all) which helps to mini-

mize the total solution size and cost. On the other hand, a

smaller ΔiLED-PP specification would require more output in-

ductance, a higher switching frequency, or additional output

capacitance.

BUCK CONVERTERS W/O OUTPUT CAPACITORS

Because current is being regulated, not voltage, a buck cur-

rent regulator is free of load current transients, therefore

output capacitance is not needed to supply the load and

maintain output voltage. This is very helpful when high fre-

quency PWM dimming the LED load. When no output capac-

itor is used, the same design equations that govern ΔiL-PP also

apply to ΔiLED-PP.

BUCK CONVERTERS WITH OUTPUT CAPACITORS

A capacitor placed in parallel with the LED load can be used

to reduce ΔiLED-PP while keeping the same average current

through both the inductor and the LED array. With an output

capacitor, the inductance can be lowered, making the mag-

netics smaller and less expensive. Alternatively, the circuit

can be run at lower frequency with the same inductor value,

improving the efficiency and increasing the maximum allow-

able average output voltage. A parallel output capacitor is

also useful in applications where the inductor or input voltage

tolerance is poor. Adding a capacitor that reduces ΔiLED-PP to

well below the target provides headroom for changes in in-

ductance or VIN that might otherwise push the maximum

ΔiLED-PP too high.

300856f2

FIGURE 9. Calculating Dynamic Resistance rD

Output capacitance (CO) is determined knowing the desired

ΔiLED-PP and the LED dynamic resistance (rD). rD can be cal-

culated as the slope of the LED’s exponential DC character-

istic at the nominal operating point as shown in Figure 9.

Simply dividing the forward voltage by the forward current at

the nominal operating point will give an incorrect value that is

5x to 10x too high. Total dynamic resistance for a string of n

LEDs connected in series can be calculated as the rD of one

device multiplied by n. The following equations can then be

used to estimate ΔiLED-PP when using a parallel capacitor:

In general, ZC should be at least half of rD to effectively reduce

the ripple. Ceramic capacitors are the best choice for the out-

put capacitors due to their high ripple current rating, low ESR,

low cost, and small size compared to other types. When se-

lecting a ceramic capacitor, special attention must be paid to

the operating conditions of the application. Ceramic capaci-

tors can lose one-half or more of their capacitance at their

rated DC voltage bias and also lose capacitance with ex-

tremes in temperature. Make sure to check any recommend-

ed deratings and also verify if there is any significant change

in capacitance at the operating voltage and temperature.

OUTPUT OVER-VOLTAGE PROTECTION

Because the LM3409/09HV controls a buck current regulator,

there is no inherent need to provide output over-voltage pro-

tection. If the LED load is opened, the output voltage will only

rise as high as the input voltage plus any ringing due to the

parasitic inductance and capacitance present at the output

node. If a ceramic output capacitor is used in the application,

it should have a minimum rating equal to the input voltage.

Ringing seen at the output node should not damage most ce-

ramic capacitors, due to their high ripple current rating.

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LM3409/LM3409HV

INPUT CAPACITORS

Input capacitors are selected using requirements for mini-

mum capacitance and RMS ripple current. The PFET current

during tON is approximately ILED, therefore the input capacitors

discharge the difference between ILED and the average input

current (IIN) during tON. During tOFF, the input voltage source

charges up the input capacitors with IIN. The minimum input

capacitance (CIN-MIN) is selected using the maximum input

voltage ripple (ΔvIN-MAX) which can be tolerated. ΔvIN-MAX is

equal to the change in voltage across CIN during tON when it

supplies the load current. A good starting point for selection

of CIN is to use ΔvIN-MAX of 2% to 10% of VIN. CIN-MIN can be

selected as follows:

An input capacitance at least 75% greater than the calculated

CIN-MIN value is recommended. To determine the RMS input

current rating (IIN-RMS) the following approximation can be

used:

Since this approximation assumes there is no inductor ripple

current, the value should be increased by 10-30% depending

on the amount of ripple that is expected. Ceramic capacitors

are the best choice for input capacitors for the same reasons

mentioned in the Buck Converters with Output Capacitors

section. Careful selection of the capacitor requires checking

capacitance ratings at the nominal operating voltage and tem-

perature.

P-CHANNEL MosFET (PFET)

The LM3409/09HV requires an external PFET (Q1) as the

main power MosFET for the switching regulator. Q1 should

have a voltage rating at least 15% higher than the maximum

input voltage to ensure safe operation during the ringing of

the switch node. In practice all switching converters have

some ringing at the switch node due to the diode parasitic

capacitance and the lead inductance. The PFET should also

have a current rating at least 10% higher than the average

transistor current (IT):

The power rating is verified by calculating the power loss

(PT) using the RMS transistor current (IT-RMS) and the PFET

on-resistance (RDS-ON):

It is important to consider the gate charge of Q1. As the input

voltage increases from a nominal voltage to its maximum in-

put voltage, the COFT architecture will naturally increase the

switching frequency. The dominant switching losses are de-

termined by input voltage, switching frequency, and PFET

total gate charge (Qg). The LM3409/09HV has to provide and

remove charge Qg from the input capacitance of Q1 in order

to turn it on and off. This occurs more often at higher switching

frequencies which requires more current from the internal

regulator, thereby increasing internal power dissipation and

eventually causing the LM3409/09HV to thermally cycle. For

a given range of operating points the only effective way to

reduce these switching losses is to minimize Qg.

A good rule of thumb is to limit Qg < 30nC (if the switching

frequency remains below 300kHz for the entire operating

range then a larger Qg can be considered). If a PFET with

small RDS-ON and a high voltage rating is required, there may

be no choice but to use a PFET with Qg > 30nC.

When using a PFET with Qg > 30nC, the bypass capacitor

(CF) should not be connected to the VIN pin. This will ensure

that peak current detection through RSNS is not affected by

the charging of the PFET input capacitance during switching,

which can cause false triggering of the peak detection com-

parator. Instead, CF should be connected from the VCC pin

to the CSN pin which will cause a small DC offset in VCST and

ultimately ILED, however it avoids the problematic false trig-

gering.

In general, the PFET should be chosen to meet the Qg spec-

ification whenever possible, while minimizing RDS-ON. This will

minimize power losses while ensuring the part functions cor-

rectly over the full operating range.

RE-CIRCULATING DIODE

A re-circulating diode (D1) is required to carry the inductor

current during tOFF. The most efficient choice for D1 is a

Schottky diode due to low forward voltage drop and near-zero

reverse recovery time. Similar to Q1, D1 must have a voltage

rating at least 15% higher than the maximum input voltage to

ensure safe operation during the ringing of the switch node

and a current rating at least 10% higher than the average

diode current (ID):

The power rating is verified by calculating the power loss

through the diode. This is accomplished by checking the typ-

ical diode forward voltage (VD) from the I-V curve on the

product datasheet and calculating as follows:

In general, higher current diodes have a lower VD and come

in better performing packages minimizing both power losses

and temperature rise.

www.national.com 14

LM3409/LM3409HV

30085616

FIGURE 10. Ideal LED Current iLED(t) During Parallel FET Dimming

EXTERNAL PARALLEL FET PWM DIMMING

Any buck topology LED driver is a good candidate for parallel

FET dimming because high slew rates are achievable, due to

the fact that no output capacitance is required. This allows for

much higher dimming frequencies than are achievable using

the EN pin. When using external parallel FET dimming, a sit-

uation can arise where maximum off-time occurs due to a

shorted output. To mitigate this situation, capacitive coupling

to the enable pin can be employed.

30085617

FIGURE 11. External Parallel FET Dimming Circuit

As shown in Figure 11, a small capacitor (CEXT) is connected

from the gate drive signal of the parallel Dim FET to the EN

pin and a pull-up resistor (REXT) is placed from the EN pin to

the external VDD supply for the Dim FET gate driver. This

forces the on-timer to restart corresponding to every rising

edge of the LED voltage, ensuring that the unwanted maxi-

mum off-time condition does not occur. With this type of

dimming, the EN pin does not control the dimming; it simply

resets the controller. A good design choice is to size REXT and

CEXT to give a time constant smaller than tOFF:

The ideal LED current waveform iLED(t) during parallel FET

PWM dimming is very similar to the EN pin PWM dimming

shown previously. The LED current does not rise and fall in-

finitely fast as shown in Figure 10 however with this method,

only the speed of the parallel Dim FET ultimately limits the

dimming frequency and dimming duty cycle. This allows for

much faster PWM dimming than can be attained with the EN

pin.

CIRCUIT LAYOUT

The performance of any switching converter depends as

much upon the layout of the PCB as the component selection.

Following a few simple guidelines will maximimize noise re-

jection and minimize the generation of EMI within the circuit.

Discontinuous currents are the most likely to generate EMI,

therefore care should be taken when routing these paths. The

main path for discontinuous current in the LM3409/09HV buck

converter contains the input capacitor (CIN), the recirculating

diode (D1), the P-channel MosFET (Q1), and the sense re-

sistor (RSNS). This loop should be kept as small as possible

and the connections between all three components should be

short and thick to minimize parasitic inductance. In particular,

the switch node (where L1, D1 and Q1 connect) should be

just large enough to connect the components without exces-

sive heating from the current it carries.

The IADJ, COFF, CSN and CSP pins are all high-impedance

control inputs which couple external noise easily, therefore

the loops containing these high impedance nodes should be

minimized. The most sensitive loop contains the sense resis-

tor (RSNS) which should be placed as close as possible to the

CSN and CSP pins to maximize noise rejection. The off-time

capacitor (COFF) should be placed close to the COFF and

GND pins for the same reason. Finally, if an external resistor

(REXT) is used to bias the IADJ pin, it should be placed close

to the IADJ and GND pins, also.

In some applications the LED or LED array can be far away

(several inches or more) from the LM3409/09HV, or on a sep-

arate PCB connected by a wiring harness. When an output

capacitor is used and the LED array is large or separated from

the rest of the converter, the output capacitor should be

placed close to the LEDs to reduce the effects of parasitic

inductance on the AC impedance of the capacitor.

15 www.national.com

LM3409/LM3409HV

Design Guide

TYPICAL APPLICATION

30085601

SPECIFICATIONS

Nominal input voltage: VIN

Maximum input voltage: VIN-MAX

Nominal output voltage (# of LEDs x forward voltage): VO

LED string dynamic resistance: rD

Switching frequency (at nominal VIN, VO): fSW

Average LED current: ILED

Inductor current ripple: ΔiL-PP

LED current ripple: ΔiLED-PP

Input voltage ripple: ΔvIN-PP

UVLO characteristics: VTURN-ON and VHYS

Expected efficiency: η

1. NOMINAL SWITCHING FREQUENCY

Calculate switching frequency (fSW) at the nominal operating

point (VIN and VO). Assume a COFF value (between 470pF and

1nF) and a system efficiency (η). Solve for ROFF:

2. INDUCTOR RIPPLE CURRENT

Set the inductor ripple current (ΔiL-PP) by solving for the ap-

propriate inductor (L1):

3. AVERAGE LED CURRENT

Set the average LED current (ILED) by first solving for the peak

inductor current (IL-MAX):

Peak inductor current is detected across the sense resistor

(RSNS). In most cases, assume the maximum value (VADJ =

1.24V) at the IADJ pin and solve for RSNS:

If the calculated RSNS is far from a standard value, the begin-

ning of the process can be iterated to choose a new ROFF, L1,

and RSNS value that is a closer fit. The easiest way to ap-

proach the iterative process is to change the nominal fSW

target knowing that the switching frequency varies with oper-

ating conditions anyways.

Another method for finding a standard RSNS value is to change

the VADJ value. However, this would require an external volt-

age source or a resistor from the IADJ pin to GND as ex-

plained in the Theory of Operation section of this datasheet.

www.national.com 16

LM3409/LM3409HV

4. OUTPUT CAPACITANCE

A minimum output capacitance (CO-MIN) may be necessary to

reduce ΔiLED-PP below ΔiL-PP. With the specified ΔiLED-PP and

the known dynamic resistance (rD) of the LED string, solve for

the required impedance (ZC) for CO-MIN:

Solve for CO-MIN:

5. INPUT CAPACITANCE

Set the input voltage ripple (ΔvIN-PP) by solving for the re-

quired minimum capacitance (CIN-MIN):

The necessary RMS input current rating (IIN-RMS) is:

6. PFET

The PFET voltage rating should be at least 15% higher than

the maximum input voltage (VIN-MAX) and current rating should

be at least 10% higher than the average PFET current (IT):

Given a PFET with on-resistance (RDS-ON), solve for the RMS

transistor current (IT-RMS) and power dissipation (PT):

7. DIODE

The Schottky diode needs a voltage rating similar to the

PFET. Higher current diodes with a lower forward voltage are

suggested. Given a diode with forward voltage (VD), solve for

the average diode current (ID) and power dissipation (PD):

8. INPUT UVLO

Input UVLO is set with the turn-on threshold voltage (VTURN-

ON) and the desired hysteresis (VHYS). To set VHYS, solve for

RUV2:

To set VTURN-ON, solve for RUV1:

9. IADJ CONNECTION METHOD

The IADJ pin controls the high-side current sense threshold

in three ways outlined in the Theory of Operation section.

Method #1: Leave IADJ pin open and ILED is calculated as in

the Average LED Current section of the Design Guide.

Method #2: Apply an external voltage (VADJ) to the IADJ pin

between 0 and 1.24V to analog dim or to reduce ILED as fol-

lows:

Keep in mind that analog dimming will eventually push the

converter in to DCM and the inductor current ripple will no

longer be constant causing a divergence from linear dimming

at low levels.

A 0.1µF capacitor connected from the IADJ pin to GND is

recommended when using this method. It may also be nec-

essary to have a 1kΩ series resistor with the capacitor to

create an RC filter. The filter will help remove high frequency

noise created by other connected circuitry.

Method #3: Connect an external resistor or potentiometer to

GND (REXT) and the internal 5µA current source will set the

voltage. Again, a 0.1µF capacitor connected from the IADJ

pin to GND is recommended. To set ILED, solve for REXT:

10. PWM DIMMING METHOD

There are two methods to PWM dim using the LM3409/09HV:

Method #1: Apply an external PWM signal to the EN terminal.

Method #2: Perform external parallel FET shunt dimming as

detailed in the External Parallel FET PWM Dimming section.

17 www.national.com

LM3409/LM3409HV

Design Example #1

EN PIN PWM DIMMING APPLICATION FOR 10 LEDS

30085618

SPECIFICATIONS

fSW = 525kHz

VIN = 48V; VIN-MAX = 75V

VO = 35V

ILED = 2A

ΔiLED-PP = ΔiL-PP = 1A

ΔvIN-PP = 1.44V

VTURN-ON = 10V; VHYS = 1.1V

η = 0.95

1. NOMINAL SWITCHING FREQUENCY

Assume COFF = 470pF and η = 0.95. Solve for ROFF:

The closest 1% tolerance resistor is 24.9 kΩ therefore the

actual tOFF and target fSW are:

The chosen components from step 1 are:

2. INDUCTOR RIPPLE CURRENT

Solve for L1:

The closest standard inductor value is 15 µH therefore the

actual ΔiL-PP is:

The chosen component from step 2 is:

www.national.com 18

LM3409/LM3409HV

3. AVERAGE LED CURRENT

Determine IL-MAX:

Assume VADJ = 1.24V and solve for RSNS:

The closest 1% tolerance resistor is 0.1 Ω therefore the ILED

is:

The chosen component from step 3 is:

4. OUTPUT CAPACITANCE

No output capacitance is necessary.

5. INPUT CAPACITANCE

Determine tON:

Solve for CIN-MIN:

Choose CIN:

Determine IIN-RMS:

The chosen components from step 5 are:

6. PFET

Determine minimum Q1 voltage rating and current rating:

A 100V, 3.8A PFET is chosen with RDS-ON = 190mΩ and Qg

= 20nC. Determine IT-RMS and PT:

The chosen component from step 6 is:

7. DIODE

Determine minimum D1 voltage rating and current rating:

A 100V, 3A diode is chosen with VD = 750mV. Determine

PD:

The chosen component from step 7 is:

19 www.national.com

LM3409/LM3409HV

8. INPUT UVLO

Solve for RUV2:

The closest 1% tolerance resistor is 49.9 kΩ therefore VHYS

is:

Solve for RUV1:

The closest 1% tolerance resistor is 6.98 kΩ therefore VTURN-

ON is:

The chosen components from step 8 are:

9. IADJ CONNECTION METHOD

The IADJ pin is left open forcing VADJ = 1.24V.

10. PWM DIMMING METHOD

PWM dimming signal pair is applied to the EN pin and GND

at fDIM = 1 kHz.

Design #1 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409HV Buck controller NSC LM3409HVMY

2 CIN1, CIN2 2.2µF X7R 10% 100V MURATA GRM43ER72A225KA01

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 Q1 PMOS 100V 3.8A ZETEX ZXMP10A18KTC

1 D1 Schottky 100V 3A VISHAY SS3H10-E3/57T

1 L1 15 µH 20% 4.2A TDK SLF12565T-150M4R2

1 ROFF 24.9kΩ 1% VISHAY CRCW060324K9FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.1Ω 1% 1W VISHAY WSL2512R1000FEA

www.national.com 20

LM3409/LM3409HV

Design Example #2

ANALOG DIMMING APPLICATION FOR 4 LEDS

30085619

SPECIFICATIONS

fSW = 500kHz

VIN = 24V; VIN-MAX = 42V

VO = 14V

ILED = 1A

ΔiL-PP = 450mA; ΔiLED-PP = 50mA

ΔvIN-PP = 1V

VTURN-ON = 10V; VHYS = 1.1V

η = 0.90

1. NOMINAL SWITCHING FREQUENCY

Assume COFF = 470pF and η = 0.90. Solve for ROFF:

The closest 1% tolerance resistor is 15.4 kΩ therefore the

actual tOFF and target fSW are:

The chosen components from step 1 are:

2. INDUCTOR RIPPLE CURRENT

Solve for L1:

The closest standard inductor value is 22 µH therefore the

actual ΔiL-PP is:

The chosen component from step 2 is:

21 www.national.com

LM3409/LM3409HV

3. AVERAGE LED CURRENT

Determine IL-MAX:

Assume VADJ = 1.24V and solve for RSNS:

The closest 1% tolerance resistor is 0.2 Ω therefore ILED is:

The chosen component from step 3 is:

4. OUTPUT CAPACITANCE

Assume rD = 2 Ω and determine ZC:

Solve for CO-MIN and :

Choose CO:

The chosen component from step 5 is:

5. INPUT CAPACITANCE

Determine tON:

Solve for CIN-MIN:

Choose CIN:

Determine IIN-RMS:

The chosen component from step 5 is:

6. PFET

Determine minimum Q1 voltage rating and current rating:

A 70V, 5.7A PFET is chosen with RDS-ON = 190mΩ and Qg =

20nC. Determine IT-RMS and PT:

The chosen component from step 6 is:

7. DIODE

Determine minimum D1 voltage rating and current rating:

A 60V, 5A diode is chosen with VD = 750mV. Determine PD:

The chosen component from step 7 is:

www.national.com 22

LM3409/LM3409HV

8. INPUT UVLO

Solve for RUV2:

The closest 1% tolerance resistor is 49.9 kΩ therefore VHYS

is:

Solve for RUV1:

The closest 1% tolerance resistor is 6.98 kΩ therefore VTURN-

ON is:

The chosen components from step 8 are:

9. IADJ CONNECTION METHOD

The IADJ pin is connected to an external voltage source and

varied from 0 – 1.24V to dim. An RC filter (RF2 = 1 kΩ and

CF2 = 0.1µF) is used as recommended.

10. PWM DIMMING METHOD

No PWM dimming is necessary.

Design #2 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409 Buck controller NSC LM3409MY

2 CIN1 4.7µF X7R 10% 50V MURATA GRM55ER71H475MA0

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 CF2 0.1µF X7R 10% 16V TDK C1608X7R1C104K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 CO2.2µF X7R 10% 50V MURATA GRM43ER71H225MA0

1 Q1 PMOS 70V 5.7A ZETEX ZXMP7A17KTC

1 D1 Schottky 60V 5A COMCHIP CDBC560-G

1 L1 22 µH 20% 4.2A TDK SLF12575T-220M4R0

1 RF2 1.0kΩ 1% VISHAY CRCW06031K00FKEA

1 ROFF 15.4kΩ 1% VISHAY CRCW060315K4FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.2Ω 1% 1W VISHAY WSL2512R2000FEA

23 www.national.com

LM3409/LM3409HV

Applications Information

DESIGN #3: EXTERNAL PARALLEL FET PWM DIMMING APPLICATION FOR 10 LEDS

30085623

Design #3 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409HV Buck controller NSC LM3409HVMY

2 CIN1, CIN2 2.2µF X7R 10% 100V MURATA GRM43ER72A225KA01

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 C1 2200pF X7R 10% 50V MURATA GRM188R71H222KA01

1 Q1 PMOS 100V 3.8A ZETEX ZXMP10A18KTC

1 Q2 CMOS 30V 2A FAIRCHILD FDC6333C

1 Q3 NMOS 100V 7.5A FAIRCHILD FDS3672

1 D1 Schottky 100V 3A VISHAY SS3H10-E3/57T

1 L1 15 µH 20% 4.2A TDK SLF12565T-150M4R2

2 R1, R2 1Ω 1% VISHAY CRCW06031R00FNEA

1 R3 10kΩ 1% VISHAY CRCW060310K0FKEA

1 REXT 100Ω 1% VISHAY CRCW0603100RFKEA

1 ROFF 24.9kΩ 1% VISHAY CRCW060324K9FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.1Ω 1% 1W VISHAY WSL2512R1000FEA

www.national.com 24

LM3409/LM3409HV

DESIGN #4: SINGLE POTENTIOMETER ANALOG DIMMING APPLICATION FOR 6 LEDS

30085622

Design #4 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409 Buck controller NSC LM3409MY

2 CIN1, CIN2 2.2µF X7R 10% 50V MURATA GRM43ER71H225MA0

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 CF2 0.1µF X7R 10% 16V TDK C1608X7R1C104K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 CO1.0µF X7R 10% 50V MURATA GRM32RR71H105KA0

1 Q1 PMOS 60V 3A ZETEX ZXMP6A17GTA

1 D1 Schottky 60V 2A ST-MICRO STPS2L60A

1 L1 68 µH 20% 2A TDK SLF12565T-680M2R0

1 ROFF 25.5kΩ 1% VISHAY CRCW060325K5FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.3Ω 1% 1W VISHAY WSL2512R3000FEA

1 RADJ 250kΩ potentiometer BOURNS 3352P-1-254

25 www.national.com

LM3409/LM3409HV

DESIGN #5: 75°C THERMAL FOLDBACK APPLICATION FOR 16 LEDS

30085624

Design #5 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409HV Buck controller NSC LM3409HVMY

1 U1 Analog Temperature

Sensor

NSC LM94022

2 CIN1, CIN2 2.2µF X7R 10% 100V MURATA GRM43ER72A225KA01

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 CF2 0.1µF X7R 10% 16V TDK C1608X7R1C104K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 Q1 PMOS 100V 3.8A ZETEX ZXMP10A18KTC

1 D1 Schottky 100V 3A COMCHIP SS3H10-E3/57T

1 L1 15 µH 20% 4.7A TDK SLF12575T-150M4R7

1 ROFF 24.9kΩ 1% VISHAY CRCW060324K9FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.07Ω 1% 1W VISHAY WSL2512R0700FEA

*U2 could be replaced with a 500kΩ NTC thermistor connected from IADJ to GND.

www.national.com 26

LM3409/LM3409HV

DESIGN #6: HIGH CURRENT APPLICATION FOR 4 LEDS

300856f4

Design #6 Bill of Materials

Qty Part ID Part Value Manufacturer Part Number

1 LM3409 Buck controller NSC LM3409MY

2 CIN1 10µF X7R 10% 50V TDK C5750X7R1H106K

1 CF1.0µF X7R 10% 16V TDK C1608X7R1C105K

1 CF2 0.1µF X7R 10% 16V TDK C1608X7R1C104K

1 COFF 470pF X7R 10% 50V TDK C1608X7R1H471K

1 CO1.0µF X7R 10% 50V MURATA GRM32RR71H105KA0

1 Q1 PMOS 30V 24A ST-MICRO STD30PF03LT4

1 D1 Schottky 30V 5A VISHAY SSC53L-E3/57T

1 L1 15 µH 20% 7.5A COILCRAFT DO5022P-153ML

1 RF2 1.0kΩ 1% VISHAY CRCW06031K00FKEA

1 ROFF 23.2kΩ 1% VISHAY CRCW060323K2FKEA

1 RUV1 6.98kΩ 1% VISHAY CRCW06036K98FKEA

1 RUV2 49.9kΩ 1% VISHAY CRCW060349K9FKEA

1 RSNS 0.05Ω 1% 1W VISHAY WSL2512R0500FEA

*U2 could be replaced with a 500kΩ NTC thermistor connected from IADJ to GND.

27 www.national.com

LM3409/LM3409HV

Physical Dimensions inches (millimeters) unless otherwise noted

10-Lead Exposed Pad Plastic eMSOP Package

NS Package Number MUC10A

www.national.com 28

LM3409/LM3409HV

Notes

29 www.national.com

LM3409/LM3409HV

Notes

LM3409 / LM3409HV PFET Buck Controller for High Power LED Drives

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