MP1523DT - Monolithic Power Systems, Inc.

MP1523

Precision 6-Lamp

White LED Driver

10/07, Rev. 1.6 www.MonolithicPo wer.com 1

Monolithic Power Systems

DESCRIPTION

The MP1523 is a 5-pin SOT23 step-up

converter designed for driving up to six (6)

series white LEDs from a single-cell Lithium

Ion battery. The MP1523 uses a current limited,

variable frequency architecture to regulate the

LED current, which is measured through an

external current sense resistor. Its low 0.4V

feedback threshold reduces power loss and

improves efficiency. To prevent damage due to

an open circuit condition, the BIAS pin can

measure the output voltage and turn off the

converter if an over-voltage condition is

present.

The MP1523 includes under-voltage lockout,

current limiting, and thermal overload

protection to prevent damage in the event of

an output overload. The MP1523 is available in

a small 5-pin SOT23 package.

FEATURES

• On Board Power MOSFET

• Drives up to 6 White LEDs

• Up to 90% Efficiency

• Over 80mA Output Current Capacity

• Open Load Shutdown

• Low 0.4V Feedback Threshold

• UVLO, Thermal Shutdown

• Soft-Start

• Internal Current Limiter

• Available in SOT23-5 Package

• Evaluation Board Available

APPLICATIONS

• Cell Phones

• Handheld Computers and PDAs

• Digital Still and Video Cameras

• Small LCD Displays

, “MPS”, “Monolithic Power Systems”, and “The Future of Analog IC

Technology” are Registered Trademarks of Monolithic Power Systems, Inc.

TYPICAL APPLICATION

MP1523

BIAS SW

FBGND

VIN

2.7V to 5.5V

Up To

6 LEDs

MP1523-TAC-S01

100

EFFICIENCY (%)

5 10152025

LED CURRENT (mA)

MP1523-EC01

= 5V

= 4V

= 3V

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

10/07, Rev. 1.6 www.MonolithicPo wer.com 2

PACKAGE REFERENCE

Part Number* Package Temperature

MP1523DT SOT23-5

-40°C to +85°C

EV0035 Evaluation Board

* For Tape & Reel, add suffix –Z (eg. MP1523DT–Z)

For Lead Free, add suffix –LF (eg. MP1523DT–LF–Z)

ABSOLUTE MAXIMUM RATINGS (1)

BIAS ...............................................-0.3V to 28V

SW ..................................................-0.5V to 28V

All Other Pins....................................-0.3V to 6V

Storage Temperature ...............-55°C to +150°C

Recommended Operating Conditions (2)

BIAS Supply Voltage ....................... 2.7V to 25V

Output Voltage....................................VIN to 25V

Operating Temperature ..............-40°C to +85°C

Thermal Resistance (3)

ΘJA (SOT23-5) ..................................... 220°C/W

ΘJC (SOT23-5) ..................................... 110°C/W

Notes:

1) Exceeding these ratings may damage the device.

2) The device is not guaranteed to function outside of its

operating conditions.

3) Measured on approximately 1” square of 1 oz copper.

ELECTRICAL CHARACTERISTICS (4)

VBIAS = VEN = 5.0V, TA = 25°C, unles s otherwise noted.

Parameter Symbol Condition Min Typ Max Units

Supply Current (shutdown) IBIAS (OFF) V

EN = 0V 1 3 μA

Supply Current (quiescent) IBIAS (ON) V

FB = 0.45V 650 750 μA

Minimum Off Time, Normal

Operation TOFF V

FB = 0V 300 550 700 ns

Minimum Off Time, Start-Up TOFF V

FB = 0V (4) 1.25 1.6 μs

Undervoltage Lockout

BIAS Under Voltage Lockout UVLO VBIAS Rising, 100mV Hysteresis 2.1 2.3 2.65 V

Open Lamp Shutdown Threshold VBIAS Rising 28 V

Enable

EN Threshold VEN Rising 0.8 1.1 1.5 V

EN Hysteresis 60 mV

EN Input Bias Current VEN = 0V, 5V 1 μA

Feedback Comparator

FB Regulation Threshold VFB Falling 380 400 420 mV

FB Hysteresis (5) 10 mV

FB Input Bias Current VFB = 0.2V -150 -80 nA

Output Switch

SW On-Resistance (5) R

ON 0.5 0.6 Ω

SW Current Limit 300 450 650 mA

SW Voltage BV ISW = 10μA 25 V

Thermal Shutdown (5) 160

°C

Thermal Shutdown Hysterisis (5) 15 °C

Notes:

4) First 64 pulses after EN switches high.

5) Guaranteed by design.

A3XX

TOP VIEW

GND

BIAS

MP1523_PD01-SOT23-5

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

10/07, Rev. 1.6 www.MonolithicPo wer.com 3

TYPICAL PERFORMANCE CHARACTERISTICS

EFFICIENCY (%)

2.5 3.0 3.5 4.0 4.5

VIN (V)

MP1523_TPC01

Efficiency vs VIN

of Figure 2

LED CURRENT (mA)

2.5 3.0 3.5 4.0 4.5

VIN (V)

MP1523_TPC02

Line Regulation

of Figure 2 and Figure 3

PIN FUNCTIONS

Pin # Name Description

1 SW Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the

power inductor and output rectifier to SW. SW can swing between GND and 25V.

2 GND Ground

3 FB Feedback Input. The MP1523 regulates the voltage across the current sense

resistor between FB and GND. Connect a current sense resistor from the bottom of

the LED string to GND. Connect the bottom of the LED string to FB. The regulation

threshold is 0.4V.

EN Regulator On/Off Control Input. A high input at EN turns on the converter, and a low

input turns it off. When not used, connect EN to the input source for automatic

startup. If EN is driven over 6V, place a resistor in series with EN to limit current to

10μA or less. Do not leave EN floating!

5 BIAS Internal Power Input. BIAS powers the internal circuitry and measures the output

voltage for open circuit protection. Connect BIAS to the output at the top of the LED

string to enable open load shutdown feature (see Figure 3). Connect BIAS to the

input to eliminate open load shutdown feature (see Figure 2).

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

10/07, Rev. 1.6 www.MonolithicPo wer.com 4

OPERATION

The MP1523 is a step-up converter that

operates from an input voltage as low as 2.7V

and generates an output voltage up to 25V. The

0.5Ω internal N-Channel power MOSFET is

driven with a variable frequency, constant-peak-

current architecture for low operating current.

The 550ns minimum off time is extended to

1.6μs during start-up to yield a smooth glitch

free turn-on.

Variable Frequency Constant-Peak-Current

Operation

When the power MOSFET is turned on the

inductor current increases until the 0.45A

current limit is reached. The internal power

MOSFET is then turned off for a minimum of

550ns. At the end of this 550ns transition if the

FB pin is still lower than the 400mV threshold

the MOSFET will again be turned on, otherwise

the MP1523 waits until the voltage drops below

the threshold before turning on the MOSFET

again. This process allows for optimal use of

the inductor, while minimizing the output ripple

and size of the output capacitor and maintaining

low operating current.

Open Load Shutdown

Open load shutdown is implemented by

connecting the BIAS pin to the output. In the

fault condition where the connection to the LED

string is open, the output voltage will rise up, as

the FB pin has no voltage. Once the output

voltage exceeds 28V, the MP1523 will cease

operation until the EN pin is cycled off and on.

Connecting the BIAS pin to VIN disables open

load shutdown but reduces the chip power

consumption due to the quiescent current.

Figure 1—Functional Block Diagram

ERROR AMP.

CURRENT

450mA

CONTROL

LOGIC

INTERNAL

POWER

BIAS

GND

400mV

(2)

(3)

(1)

(5)

(4)

REGULATOR

Open Load

Shutdown

Comparato

1.23V

160K

17V

20K

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

10/07, Rev. 1.6 www.MonolithicPo wer.com 5

APPLICATIONS INFORMATION

Setting the LED current

The LED current is set by the sense resistor

(R2) at FB. The LED current can be calculated

as:

IFB

LED =

Where VFB is 400mV. The LED current is set to

20mA if R2 = 20Ω.

Capacitor Selection

A 1μF to 10μF ceramic input capacitor (C1) and

a 0.47μF to 1μF ceramic output capacitor (C2)

are recommended for most applications. A

capacitor (typically 1nF) in parallel with the LED

string improves stability, input and output ripple

especially when large inductance values (10μH

or above) are used. For best stability over a

wide temperature range, use capacitors with an

X5R or X7R dielectric.

Inductor selection

The MP1523 has a 450mA inductor current limit

and can drive up to 6 LEDs at 20mA.

Inductance values (L1) from 4.7μH to 47μH

work satisfactorily. Larger values provide the

best efficiency while small inductor values allow

the smallest inductor size. To prevent

saturation, use an inductor with a saturation

current rating that matches the device current

limit.

Diode selection

The MP1523’s high switching frequency

demands a high-speed rectifier (D1) for

optimum efficiency. A schottky diode is

recommended due to its fast recovery time and

low forward voltage drop. Ensure the diode’s

average and peak current ratings exceed the

average output current and peak inductor

current. In addition, the diode’s reverse

breakdown voltage must exceed the output

voltage.

Layout

Careful PC board layout is required due to fast-

switching. All components must be placed as

close to the IC as possible. Keep the path

between inductor L1, diode D1, and output

capacitor C2 extremely short for minimal noise

and ringing. The feedback components such as

sense resistor R2 must be kept close to the FB

pin to prevent noise injection on the FB pin

trace. The ground return of C1 and C2 should

be tied close to the GND pin. See the MP1523

demo board layout for reference.

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

10/07, Rev. 1.6 www.MonolithicPo wer.com 6

TYPICAL APPLICATIONS / TEST CIRCUITS

Figure 2—One String of up to Six (6) LEDs “without” Open Load Shutdown Option

Up to

6 LEDs

MP1523

BIAS

GND

VIN = 2. 7 to 25V

D1, B130

4.7礔

15礖

CDM4D11

1礔

20Ω

Po i n t B

No te: Pin 5 connects t o Point B to enable Open Load Shutdown Optio n

Figure 3—One String of up to Six (6) LEDs “with” Open Load Shutdown Option

Up to

6 LEDs

MP1523

BIAS

GND

VIN = 2.7 to 25V

D1, B130

4.7礔

15礖

CDM4D11

1礔

20Ω

Point A

Note: Pin 5 connects to Point A to elimi n ate Open L o ad Shutdown Option

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

NOTICE: MPS believes the information in this document to be accurate and reliable. However, it is subject to change without

notice. Contact MPS for current specifications. MPS encourages users of its products to ensure that third party Intellectual

Property rights are not infringed upon when integrating MPS products into any application. MPS cannot assume any legal

responsibility for any said applications.

MP1523 Rev. 1.6 Monolithic Power Systems, Inc. 7

10/11/07 983 University Avenue, Building A, Los Gatos, CA 95032 USA

PACKAGE INFORMATION

SOT23-5

0.45

0皛3

10 TYP.

(2 plcs)

0.20 BSC.

Gauge Plane ?.10

0.127 TYP

10 TYP.

(2 plcs)

0.05(MIN)

1.15? .150

10 TYP.

(2 plcs)

10 TYP.

SEATING PLANE

0.15(MAX)

1.60? .100

2.80? .200

2.90? .100

0.950 0.950

0.350(MIN)

TYP. TYP.

(5 PLCS)

0.500(MAX)