General Description
The MAX5090A/B/C easy-to-use, high-efficiency, high-
voltage step-down DC-DC converters operate from an
input voltage up to 76V, and consume only 310µA qui-
escent current at no load. This pulse-width-modulated
(PWM) converter operates at a fixed 127kHz switching
frequency at heavy loads, and automatically switches
to pulse-skipping mode to provide low quiescent cur-
rent and high efficiency at light loads. The MAX5090
includes internal frequency compensation simplifying
circuit implementation. The device can also be syn-
chronized with external system clock frequency in a
noise-sensitive application. The MAX5090 uses an
internal low on-resistance and a high-voltage DMOS
transistor to obtain high efficiency and reduce overall
system cost. This device includes undervoltage lock-
out, cycle-by-cycle current limit, hiccup-mode output
short-circuit protection, and overtemperature shutdown.
The MAX5090 delivers up to 2A output current. External
shutdown is included, featuring 19µA (typ) shutdown
current. The MAX5090A/MAX5090B versions have fixed
output voltages of 3.3V and 5V, respectively, while the
MAX5090C features an adjustable 1.265V to 11V output
voltage.
The MAX5090 is available in a space-saving 16-pin thin
QFN package (5mm x 5mm) and operates over the
automotive temperature range (-40°C to +125°C).
Applications
Automotive
Industrial
Distributed Power
Features
♦Wide Input Voltage Range: 6.5V to 76V
♦Fixed (3.3V, 5V) and Adjustable (1.265V to 11V)
Output-Voltage Versions
♦2A Output Current
♦Efficiency Up to 92%
♦Internal 0.26ΩHigh-Side DMOS FET
♦310µA Quiescent Current at No Load
♦19µA Shutdown Current
♦Internal Frequency Compensation
♦Fixed 127kHz Switching Frequency
♦External Frequency Synchronization
♦Thermal Shutdown and Short-Circuit Current Limit
♦-40°C to +125°C Automotive Temperature Range
♦16-Pin (5mm x 5mm) Thin QFN Package
♦Capable of Dissipating 2.67W at +70°C
MAX5090A/B/C
2A, 76V, High-Efficiency
MAXPower Step-Down DC-DC Converters
________________________________________________________________ Maxim Integrated Products 1
15
16
14
13
6
5
7
LX
VIN
8
LX
N.C.
ON/OFF
PGND
12
DRAIN
4
12
EP
11 9
N.C.
N.C.
FB
SS
SYNC
VD
MA5090
BST SGND
3
10
DRAIN
TQFN
TOP VIEW
Pin Configuration
PGND
BST
LX
VIN
SGND
FB
VOUT
5V/2A
VD
100µH
CBST
0.22µF
3.3µF
ON/OFF COUT
100µF
SS
SYNC
D1
PDS5100H
DRAIN
CSS
0.047µF
CIN
68µF
CBYPASS
0.47µF
RIN
10Ω
VIN
7.5V TO 76V
MAX5090B
Typical Operating Circuit
19-3872; Rev 0; 3/06
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP
RANGE
PIN-
PACKAGE*
OUTPUT
VOLTAGE
(V)
MAX5090AATE+
-40°C to +125°C 16 TQFN-EP**
3.3
MAX5090AATE
-40°C to +125°C 16 TQFN-EP**
3.3
MAX5090BATE+
-40°C to +125°C 16 TQFN-EP**
5.0
MAX5090BATE
-40°C to +125°C 16 TQFN-EP**
5.0
Ordering Information
Ordering Information continued at end of data sheet.
*The package code is T1655-3.
**EP = Exposed pad.
+Denotes lead-free package.
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed under "Absolute Maximum Ratings" may cause damage to the device. These are stress ratings only, and functional operation of
the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maxi-
mum rating conditions for extended periods may affect device reliability.
(Voltages referenced to PGND, unless otherwise specified.)
VIN, DRAIN .............................................................-0.3V to +80V
SGND, PGND.………………………………………-0.3V to +0.3V
LX.................................................................-0.8V to (VIN + 0.3V)
BST ...............................................................-0.3V to (VIN + 10V)
BST to LX................................................................-0.3V to +10V
ON/OFF........................................................-0.3V to (VIN + 0.3V)
VD, SYNC ...............................................................-0.3V to +12V
SS…………………………………………………………-0.3 to +4V
FB
MAX5090A/MAX5090B…………….……… ...….-0.3V to +15V
MAX5090C ................1mA (internally clamped to +2V, -0.3V)
VOUT Short-Circuit Duration………………………… ...Continuous
VD Short-Circuit Duration………….............................Continuous
Continuous Power Dissipation (TA= +70°C)*
16-Pin TQFN (derate 33.3mW/°C above +70°C) ........2.667W
Operating Junction Temperature Range...........-40°C to +125°C
Storage Temperature Range .........................…-65°C to +150°C
Junction Temperature……...……………………………….+150°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at
TA= +25°C. See the Typical Operating Circuit.) (Note 1)
*As per JEDEC 51 Standard Multilayer Board.
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
Input Voltage Range VIN 6.5
76.0
V
Undervoltage Lockout UVLO VIN rising
5.70 6.17 6.45
V
UVLO Hysteresis
UVLOHYS
0.5 V
MAX5090A
VIN = 6.5V to 76V, IOUT = 0 to 2A
3.20
3.3
3.39
MAX5090B
VIN = 7.5V to 76V, IOUT = 0 to 2A
4.85
5.0
5.15
Output Voltage VOUT
MAX5090B
VIN = 7V to 76V, IOUT = 0 to 1A
4.85
5.0
5.15
V
Output Voltage Range VOUT MAX5090C only
1.265 11.000
V
Feedback Voltage VFB MAX5090C, VIN = 6.5V to 76V
1.191 1.228 1.265
V
MAX5090A
VIN = 12V, IOUT = 1A 80
MAX5090B
VIN = 12V, IOUT = 1A 88Efficiency η
MAX5090C
VIN = 12V, VOUT = 5V, IOUT = 1A 88
%
MAX5090A
VIN = 6.5V to 28V 310
550
MAX5090B
VIN = 7V to 28V 310
550
Quiescent Supply Current
(Note 2) IQ
MAX5090C
VIN = 6.5V to 28V 310
550
µA
MAX5090A
VIN = 6.5V to 40V 310
570
MAX5090B
VIN = 7V to 40V 310
570
Quiescent Supply Current
(Note 2) IQ
MAX5090C
VIN = 6.5V to 40V 310
570
µA
MAX5090A
VIN = 6.5V to 76V 310
650
MAX5090B
VIN = 7V to 76V 310
650
Quiescent Supply Current
(Note 2) IQ
MAX5090C
VIN = 6.5V to 76V 310
650
µA
Shutdown Current ISHDN VON/OFF = 0V, VIN = 14V 19 45 µA
SOFT-START
Default Internal Soft-Start
Period CSS = 0 700 µs
Soft-Start Charge Current
ISS 4.5 10
16.0
µA
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at
TA= +25°C. See the Typical Operating Circuit.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Soft-Start Reference Voltage
VSS
REF
1.23 1.46 1.65
V
INTERNAL SWITCH/CURRENT LIMIT
Peak Switch Current Limit ILIM (Note 3) 2.4 3.3 5.0 A
Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V -10
+10
µA
Switch On-Resistance
RDS
ON
ISWITCH = 1A
0.26
0.4 Ω
PFM Threshold IPFM Minimum switch current in any cycle 1 60
300
mA
PFM Threshold IPFM Minimum switch current in any cycle at TJ ≤ +25°C
(Note 4) 14
300
mA
FB Input Bias Current IBMAX5090C, VFB = 1.2V
-150 +0.1 +150
nA
ON/OFF CONTROL INPUT
ON/OFF Input-Voltage
Threshold
VON/OFF
Rising trip point
1.180 1.38 1.546
V
ON/OFF Input-Voltage
Hysteresis VHYST 100 mV
ON/OFF Input Current
ION/OFF
VON/OFF = 0V to VIN 10
100
nA
OSCILLATOR/SYNCHRONIZATION
Oscillator Frequency f0SC 106
127 150
kHz
Synchronization fSYNC
119 200
kHz
Maximum Duty Cycle DMAX VIN = 6.5V to 76V, VOUT ≤ 11V 80 95 %
SYNC High-Level Voltage 2.0 V
SYNC Low-Level Voltage 0.8 V
SYNC Minimum Pulse Width
350
ns
SYNC Input Leakage -1 +1 µA
INTERNAL VOLTAGE REGULATOR
Regulator Output Voltage VD VIN = 9V to 76V, IOUT = 0 7.0 7.8 8.4 V
Dropout Voltage 6.5V ≤ VIN ≤ 8.5V, IOUT = 15mA 0.5 V
Load Regulation
∆VD/∆IVD
0 to 15mA 10 Ω
PACKAGE THERMAL CHARACTERISTICS
Thermal Resistance
(Junction to Ambient) θJA TQFN package (JEDEC 51) 30
°C/W
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature TSH Temperature rising
+175
°C
Thermal-Shutdown
Hysteresis THYST 20 °C
Note 1: All limits at -40°C are guaranteed by design, not production tested.
Note 2: For total current consumption during switching (at no load), also see the Typical Operating Characteristics.
Note 3: Switch current at which the current-limit circuit is activated.
Note 4: Limits are guaranteed by design.
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
4_______________________________________________________________________________________
Typical Operating Characteristics
(VIN = 12V, VON/OFF =12V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C. See the Typical
Operating Circuit, if applicable.)
3.20
3.24
3.22
3.28
3.26
3.32
3.30
3.34
3.38
3.36
3.40
-50 0 25-25 50 75 100 125 150
VOUT vs. TEMPERATURE
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc01
AMBIENT TEMPERATURE (°C)
VOUT (V)
IOUT = 0
IOUT = 2A
4.85
4.90
4.95
5.00
5.05
5.10
5.15
-50 0-25 25 50 75 100 125 150
VOUT vs. TEMPERATURE
(MAX5090BATE, VOUT = 5V)
MAX5090 toc02
AMBIENT TEMPERATURE (°C)
VOUT (V)
IOUT = 0
IOUT = 2A
3.20
3.26
3.24
3.22
3.30
3.28
3.38
3.36
3.34
3.32
3.40
6.5 16 26 36 46 56 66 76
LINE REGULATION
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc03
VIN (V)
VOUT (V)
IOUT = 0
IOUT = 2A
4.85
4.95
4.90
5.05
5.00
5.10
5.15
6.5 36 4616 26 56 66 76
LINE REGULATION
(MAX5090BATE, VOUT = 5V)
MAX5090 toc04
VIN (V)
VOUT (V)
IOUT = 0
IOUT = 2A
ILOAD (mA)
VOUT (V)
LOAD REGULATION
(MAX5090AATE, VOUT = 3.3V)
3.38
3.40
3.32
3.34
3.36
0.1 1 10 100 1000 10,000
MAX5090 toc05
3.28
3.30
3.22
3.24
3.26
3.20
VIN = 76V
VIN = 24V
VIN = 6.5V
ILOAD (mA)
VOUT (V)
LOAD REGULATION
(MAX5090BATE, VOUT = 5V)
5.15
5.10
5.05
5.00
MAX5090 toc06
4.95
4.90
4.85
0.1 1 10 100 1000 10,000
VIN = 24V
VIN = 76V
VIN = 6.5V
0
30
20
10
40
50
60
70
80
90
100
0 800400 1200 1600 2000
EFFICIENCY vs. LOAD CURRENT
(MAX5090AATE, VOUT = 3.3V)
MAX5090 toc07
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 76V
VIN = 48V
VIN = 24V
VIN = 12V
VIN = 6.5V
0
30
20
10
40
50
60
70
80
90
100
0 800400 1200 1600 2000
EFFICIENCY vs. LOAD CURRENT
(MAX5090BATE, VOUT = 5V)
MAX5090 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 6.5V
VIN = 76V
VIN = 48V
VIN = 24V
VIN = 12V
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-50 0-25 25 50 75 100 125 150
OUTPUT CURRENT LIMIT vs. TEMPERATURE
(MAX5090AATE)
MAX5090 toc09
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT LIMIT (A)
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C. See the Typical
Operating Circuit, if applicable.)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-50 0-25 25 50 75 100 125 150
OUTPUT CURRENT LIMIT vs. TEMPERATURE
(MAX5090BATE)
MAX5090 toc010
AMBIENT TEMPERATURE (°C)
OUTPUT CURRENT LIMIT (A)
VOUT = 5V
5% DROP IN VOUT
PULSED OUTPUT LOAD
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE
(MAX5090AATE)
MAX5090 toc11
INPUT VOLTAGE (V)
OUTPUT CURRENT LIMIT (A)
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE
(MAX5090BATE)
MAX5090 toc12
INPUT VOLTAGE (V)
OUTPUT CURRENT LIMIT (A)
VOUT = 5V
5% DROP IN VOUT
PULSED OUTPUT LOAD
300
350
400
450
500
550
600
-50 0-25 25 50 75 100 125 150
NO-LOAD SUPPLY CURRENT vs. TEMPERATURE
(MAX5090AATE)
MAX5090 toc13
AMBIENT TEMPERATURE (°C)
NO-LOAD SUPPLY CURRENT (µA)
VOUT = 3.3V
300
400
350
500
450
550
600
6.5 36 4616 26 56 66 76
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
(MAX5090AATE)
MAX5090 toc14
INPUT VOLTAGE (V)
NO-LOAD SUPPLY CURRENT
VOUT = 3.3V
10
14
22
18
26
30
-50 0 25-25 50 100 125 150 175
SHUTDOWN CURRENT vs. TEMPERATURE
(MAX5090AATE)
MAX5090 toc15
AMBIENT TEMPERATURE (°C)
SHUTDOWN CURRENT (µA)
VOUT = 3.3V
0
10
5
25
20
15
40
35
30
45
6.5 36 4616 26 56 66 76
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX5090 toc16
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
VOUT = 3.3V
0
3
6
9
11
13
59107861111.5 12 12.5 13
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX5090 toc17
VIN (V)
VOUT (V)
IOUT = 0A
IOUT = 1A
IOUT = 2A
MAX5090CATE
VOUT = 11V
VON/OFF = VIN
MAX5090 toc18
LOAD-TRANSIENT RESPONSE
(MAX5090AATE)
VOUT = 3.3V
A: VOUT, 200mV/div, AC-COUPLED
B: IOUT, 1A/div, 1A TO 2A
400µs/div
A
B
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
6_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF =12V, TA= TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TA= +25°C. See the Typical
Operating Circuit, if applicable.)
MAX5090 toc19
LOAD-TRANSIENT RESPONSE
(MAX5090AATE)
VOUT = 3.3V
A: VOUT, 200mV/div, AC-COUPLED
B: IOUT, 500mA/div, 0.1A TO 1A
400µs/div
A
B
LX WAVEFORMS
(MAX5090AATE)
MAX5090 toc20
VOUT = 3.3V
A
B
A: SWITCH VOLTAGE (LX PIN), 20mV/div (VIN = 48V)
B: INDUCTOR CURRENT, 2A/div (I0 = 2A)
4µs/div
0
MAX5090 toc21
LX WAVEFORMS
(MAX5090AATE)
VOUT = 3.3V
A: SWITCH VOLTAGE, 20V/div (VIN = 48V)
B: INDUCTOR CURRENT, 200mA/div (I0 = 75mA)
4µs/div
A
B
MAX5090 toc22
LX WAVEFORM
(MAX5090AATE)
VOUT = 3.3V
A: SWITCH VOLTAGE, 20V/div (VIN = 48V)
B: INDUCTOR CURRENT, 200mA/div (IOUT = 0)
4µs/div
A
B
MAX5090 toc23
STARTUP WAVEFORM
(IOUT = 0)
A: VON/OFF, 2V/div
B: VOUT, 1V/div
4ms/div
A
B
CSS = 0.047µF
MAX5090 toc24
STARTUP WAVEFORM
(IOUT = 2A)
A: VON/OFF, 2V/div
B: VOUT, 1V/div
4ms/div
A
B
CSS = 0.047µF
1.0
3.0
2.0
5.0
4.0
6.0
7.0
6.5 36 4616 26 56 66 76
PEAK SWITCH CURRENT
vs. INPUT VOLTAGE
MAX5090 toc25
INPUT VOLTAGE (V)
PEAK SWITCH CURRENT (A)
MAX5090AATE
VOUT = 3.3V
5% DROP IN VOUT
PULSED OUTPUT LOAD
MAX5090 toc26
SYNCHRONIZATION
fSYNC = 119kHz
SYNC
2V/div
LX
10V/div
2µs/div
MAX5090 toc27
fSYNC = 200kHz
SYNCHRONIZATION
1µs/div
SYNC
2V/div
LX
10V/div
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
_______________________________________________________________________________________ 7
Pin Description
PIN NAME FUNCTION
1, 2 LX Source Connection of Internal High-Side Switch
3BST Boost Capacitor Connection. Connect a 0.22µF ceramic capacitor from BST to LX.
4V
IN Input Voltage. Bypass VIN to SGND with a low-ESR capacitor as close to the device as possible.
5VDInternal Regulator Output. Bypass VD to PGND with a 3.3µF/10V or greater ceramic capacitor.
6SYNC Synchronization Input. Connect SYNC to an external clock for synchronization. Connect to SGND to
select the internal 127kHz switching frequency.
7SS
Soft-Start Capacitor Connection. Connect an external capacitor from SS to SGND to adjust the soft-
start time.
8FB
Output Sense Feedback Connection.
For fixed output voltage (MAX5090A/MAX5090B), connect FB to VOUT.
For adjustable output voltage (MAX5090C), use an external resistive voltage-divider to set VOUT. VFB
regulating set point is 1.228V.
9ON/OFF Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for
normal operation. Connect ON/OFF to VIN with short leads for always-on operation.
10 SGND Signal Ground. SGND must be connected to PGND for proper operation.
11, 15, 16
N.C. No Connection. Not internally connected.
12 PGND Power Ground
13, 14 DRAIN Internal High-Side Switch Drain Connection
—EP
Exposed Pad. Solder EP to SGND plane to aid in heat dissipation. Do not use as the only electrical
ground connection.
Detailed Description
The MAX5090 step-down DC-DC converter operates
from a 6.5V to 76V input voltage range. A unique volt-
age-mode control scheme with voltage feed-forward
and an internal switching DMOS FET provides high effi-
ciency over a wide input voltage range. This pulse-
width-modulated converter operates at a fixed 127kHz
switching frequency or can be synchronized with an
external system clock frequency. The device also fea-
tures automatic pulse-skipping mode to provide high
efficiency at light loads. Under no load, the MAX5090
consumes only 310µA, and in shutdown mode, con-
sumes only 20µA. The MAX5090 also features under-
voltage-lockout, hiccup-mode output short-circuit
protection and thermal shutdown.
ON/
OFF
/Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the external UVLO
threshold at the input. Connect a resistive voltage-
divider from VIN to SGND with the center node to
ON/OFF, as shown in Figure 1. Calculate the threshold
value by using the following formula:
Set the external VUVLO(TH) to greater than 6.45V. The
maximum recommended value for R2 is less than 1MΩ.
ON/OFF is a logic input and can be safely driven to the
full VIN range. Connect ON/OFF to VIN for automatic
startup. Drive ON/OFF to ground to shut down the
MAX5090. Shutdown forces the internal power MOSFET
off, turns off all internal circuitry, and reduces the VIN
supply current to 20µA (typ). The ON/OFF rising thresh-
old is 1.546V (max). Before any operation begins, the
voltage at ON/OFF must exceed 1.546V. The ON/OFF
input has 100mV hysteresis.
If the external UVLO threshold setting divider is not
used, an internal undervoltage-lockout feature monitors
the supply voltage at VIN and allows the operation to
start when VIN rises above 6.45V (max). The internal
UVLO rising threshold is set at 6.17V with 0.5V hystere-
sis. The VIN and VON/OFF voltages must be above 6.5V
and 1.546V, respectively, for proper operation.
VR
Rx
UVLO TH() .=+
11
2138
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
8_______________________________________________________________________________________
MAX5090
REGULATOR
(FOR ANALOG)
ENABLE
LX
BST
VIN
ON/OFF
VREF
REGULATOR
(FOR DRIVER) OSC RAMP
IREF-PFM
IREF-LIM
CPFM
1.38V
CILIM
FB
EAMP
THERMAL
SHUTDOWN
CPWM
VD
PGND
RAMP
CLK
CONTROL
LOGIC
TYPE 3
COMPENSATION
SGND
x1
*RH
DRAIN
SYNC
SS
MIN
SRAMP MUX
SRMP
SCK
*RL
CLKI RMP
N
HIGH-SIDE
CURRENT SENSE
*RH = 0Ω AND RL = ∞ FOR MAX5090C
Simplified Functional Diagram
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
_______________________________________________________________________________________ 9
Boost High-Side Gate Drive (BST)
Connect a flying bootstrap capacitor between LX and
BST to provide the gate-drive voltage to the high-side
n-channel DMOS switch. The capacitor is alternately
charged from the internally regulated output-voltage VD
and placed across the high-side DMOS driver. Use a
0.22µF, 16V ceramic capacitor located as close to the
device as possible.
On startup, an internal low-side switch connects LX to
ground and charges the BST capacitor to (VD - VDIODE).
Once the BST capacitor is charged, the internal low-side
switch is turned off and the BST capacitor voltage pro-
vides the necessary enhancement voltage to turn on the
high-side switch.
Synchronization (SYNC)
SYNC controls the oscillator frequency. Connect SYNC
to SGND to select 127kHz operation. Use the SYNC
input to synchronize to an external clock. SYNC has a
guaranteed frequency range of 119kHz to 200kHz
when using an external clock.
When SYNC is connected to SGND, the internal clock
is used to generate a ramp with the amplitude in pro-
portion to VIN and the period corresponding to the
internal clock frequency to modulate the duty cycle of
the high-side switch.
If an external clock (SYNC clock) is applied at SYNC for
four cycles, the MAX5090 selects the SYNC clock. The
MAX5090 generates a ramp (SYNC ramp) with the
amplitude in proportion to VIN and the period corre-
sponding to the SYNC clock frequency. The MAX5090
initially blanks the SYNC ramp for 375µs (typ) to allow
the ramp to reach its target amplitude (proportion to the
VIN supply). After the SYNC blanking time, the SYNC
ramp and the SYNC clock switch to the PWM controller
and replace the internal ramp and the internal clock,
respectively. If the SYNC clock is removed for three
internal clock cycles, the internal clock and the internal
ramp switch back to the PWM controller.
The minimum pulse-width requirement for the external
clock is 350ns, and if the requirement is not met, the
MAX5090 could ignore the clock as a noisy bounce.
Soft-Start (SS)
The MAX5090 provides the flexibility to externally pro-
gram a suitable soft-start time for a given application.
Connect an external capacitor from SS to SGND to use
the external soft-start. Soft-start gradually ramps up the
reference voltage seen by the error amplifier to control
the output’s rate of rise and reduce the input surge cur-
rent during startup. For soft-start time longer than 700µs,
use the following equation to calculate the soft-start
capacitor (CSS) required for the soft-start time (tSS):
where tSS > 700µs and CSS is in Farads.
The MAX5090 also provides an internal soft-start
(700µs, typ) with a current source to charge an internal
capacitor to rise up to the bandgap reference voltage.
The internal soft-start voltage will eventually be pulled
up to 3.4V. The internal soft-start reference also feeds
to the error amplifier. The error amplifier takes the low-
est voltage among SS, the internal soft-start voltage,
and the bandgap reference voltage as the input refer-
ence for VOUT.
Soft-start occurs when power is first applied and when
the device exits shutdown. The MAX5090 also goes
through soft-start when coming out of thermal-overload
protection. During a soft-start, if the voltage at SS (VSS)
is charged up to 1.46V in less than 700µs, the
MAX5090 takes its default internal soft-start (700µs) to
ramp up as its reference. After the SS and the internal
soft-start ramp up over the bandgap reference, the
error amplifier takes the bandgap reference.
Thermal-Overload Protection
The MAX5090 features integrated thermal-overload
protection. Thermal-overload protection limits power
dissipation in the device, and protects the device from
a thermal overstress. When the die temperature
exceeds +175°C, an internal thermal sensor signals the
shutdown logic, turning off the internal power MOSFET,
resetting the internal soft-start and allowing the IC to
cool. The thermal sensor turns the internal power
MOSFET back on after the IC’s die temperature cools
down to +155°C, resulting in a pulsed output under
continuous thermal-overload conditions.
CSS =××
−
10 10
146
6
.
tSS
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
10 ______________________________________________________________________________________
PGND
BST
LX
VIN
SGND
FB
VOUT
3.3V, 2A
R1
VD
0.22µF
100µH
3.3µF
R2
ON/OFF COUT
100µF
SS
SYNC
D1
PDS5100H
DRAIN
0.047µF
CIN
68µFCBYPASS
0.47µF
RIN
10Ω
VIN
6.5V TO 76V
MAX5090A
MAX5090C
PGND
BST
LX
VIN
SGND
FB
VD
SS
SYNC
DRAIN
VOUT
5.25V, 2A
0.22µF
100µH
3.3µF
COUT
100µF
D1
PDS5100H
0.047µF
CIN
68µF
VIN
7.5V TO 76V
CBYPASS
0.47µF
RIN
10Ω
R4
R3
ON/OFF
Figure 1. Fixed Output-Voltage Configuration
Figure 2. Adjustable Output-Voltage Configuration
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
______________________________________________________________________________________ 11
Thermal-overload protection is intended to protect the
MAX5090 in the event of a fault condition. For normal
circuit operation, do not exceed the absolute maximum
junction temperature rating of TJ= +150°C.
Setting the Output Voltage
The MAX5090A/MAX5090B have preset output volt-
ages of 3.3V and 5.0V, respectively. Connect FB to
VOUT for the preset output voltage (Figure 1).
The MAX5090C offers an adjustable output voltage. Set
the output voltage with a resistive divider connected
from the circuit’s output to ground (Figure 2). Connect
the center node of the divider to FB. Choose R4 less
than 15kΩ, then calculate R3 as follows:
The MAX5090 features internal compensation for opti-
mum closed-loop bandwidth and phase margin.
Because of the internal compensation, the output must
be sensed immediately after the primary LC.
Inductor Selection
The MAX5090 is a fixed-frequency converter with fixed
internal frequency compensation. The internal fixed
compensation assumes a 100µH inductor and 100µF
output capacitor with 50mΩESR. It relies on the loca-
tion of the double LC pole and the ESR zero frequency
for proper closed-loop bandwidth and the phase mar-
gin at the closed-loop unity-gain frequency. See Table
2 for proper component values. Usually, the choice of
an inductor is guided by the voltage difference
between VIN and VOUT, the required output current and
the operating frequency of the circuit. However, use the
recommended inductors in Table 2 to ensure stable
operation with optimum bandwidth.
Use an inductor with a maximum saturation current rat-
ing greater than or equal to the maximum peak current
limit (5A). Use inductors with low DC resistance for a
higher efficiency converter.
Selecting a Rectifier
The MAX5090 requires an external Schottky rectifier as
a freewheeling diode. Connect this rectifier close to the
device using short leads and short PC board traces.
The rectifier diode must fully conduct the inductor cur-
rent when the power FET is off to have a full rectifier
function. Choose a rectifier with a continuous current
rating greater than the highest expected output current.
Use a rectifier with a voltage rating greater than the
maximum expected input voltage, VIN. Use a low for-
ward-voltage Schottky rectifier for proper operation and
high efficiency. Avoid higher than necessary reverse-
voltage Schottky rectifiers that have higher forward-volt-
age drops. Use a Schottky rectifier with forward-voltage
drop (VF) less than 0.55V and 0.45V at +25°C and
+125°C, respectively, and at maximum load current to
avoid forward biasing of the internal parasitic body
diode (LX to ground). See Figure 3 for forward-voltage
drop vs. temperature of the internal body diode of the
MAX5090. Internal parasitic body-diode conduction
may cause improper operation, excessive junction tem-
perature rise, and thermal shutdown. Use Table 1 to
choose the proper rectifier at different input voltages
and output current.
Input Bypass Capacitor
The discontinuous input current waveform of the buck
converter causes large ripple currents in the input
capacitor. The switching frequency, peak inductor cur-
rent, and the allowable peak-to-peak voltage ripple
reflecting back to the source dictate the capacitance
requirement. The MAX5090 high switching frequency
allows the use of smaller value input capacitors.
The input ripple is comprised of ∆VQ(caused by the
capacitor discharge) and ∆VESR (caused by the ESR of
the capacitor). Use low-ESR aluminum electrolytic
capacitors with high-ripple current capability at the input.
Assuming that the contribution from the ESR and capaci-
tor discharge is equal to 90% and 10%, respectively, cal-
culate the input capacitance and the ESR required for a
specified ripple using the following equations:
R3 =−
(.)
.
VxR
OUT 1 228
1 228 4
Table 1. Diode Selection
VIN (V) DIODE PART
NUMBER MANUFACTURER
B340LB Diodes Inc.
RB051L-40
Central Semiconductor
6.5 to 36
MBRS340T3 ON Semiconductor
MBRM560 Diodes Inc.
RB095B-60
Central Semiconductor
6.5 to 56
MBRD360T4 ON Semiconductor
50SQ80 IR
6.5 to 76
PDS5100H Diodes Inc.
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
12 ______________________________________________________________________________________
where:
IOUT is the maximum output current of the converter
and fSW is the oscillator switching frequency (127kHz).
For example, at VIN = 48V, VOUT = 3.3V, the ESR and
input capacitance are calculated for the input peak-to-
peak ripple of 100mV or less, yielding an ESR and
capacitance value of 40mΩand 100µF, respectively.
Low-ESR ceramic multilayer chip capacitors are recom-
mended for size-optimized application. For ceramic
capacitors assume the contribution from ESR and capaci-
tor discharge is equal to 10% and 90%, respectively.
The input capacitor must handle the RMS ripple current
without significant rise in the temperature. The maxi-
mum capacitor RMS current occurs at approximately
50% duty cycle. Ensure that the ripple specification of
the input capacitor exceeds the worst-case capacitor
RMS ripple current. Use the following equations to cal-
culate the input capacitor RMS current:
where:
IPRMS is the input switch RMS current, IAVGin is the
input average current, and ηis the converter efficiency.
The ESR of the aluminum electrolytic capacitor increas-
es significantly at cold temperatures. Use a 1µF or
greater value ceramic capacitor in parallel with the alu-
minum electrolytic input capacitor, especially for input
voltages below 8V.
Output Filter Capacitor
The output capacitor COUT forms double pole with the
inductor and a zero with its ESR. The MAX5090’s inter-
nal fixed compensation is designed for a 100µF capaci-
tor, and the ESR must be from 20mΩto 100mΩ. The
use of an aluminum or tantalum electrolytic capacitor is
recommended. See Table 2 to choose an output
capacitor for stable operation.
The output ripple is comprised of ∆VOQ (caused by the
capacitor discharge), and ∆VOESR (caused by the ESR
of the capacitor). Use low-ESR tantalum or aluminum
electrolytic capacitors at the output. Use the following
equations to calculate the contribution of output capac-
itance and its ESR on the peak-to-peak output ripple
voltage:
The MAX5090 has a programmable soft-start time (tSS).
The output rise time is directly proportional to the out-
put capacitor, output voltage, and the load. The output
rise time also depends on the inductor value and the
current-limit threshold. It is important to keep the output
rise time at startup the same as the soft-start time (tSS)
to avoid output overshoot. Large output capacitors take
longer than the programmed soft-start time (tSS) and
cause error-amplifier saturation. This results in output
overshoot. Use greater than 2ms soft-start time for a
100µF output capacitor.
∆∆
∆∆
VIxESR
VI
xC x f
OESR L
OQ L
OUT SW
=
≈
8
III x
D
IVI
Vx
II I
II I
DV
V
PRMS PK DC IPK xIDC
AVGin
OUT x OUT
IN
PK OUT L
DC OUT L
OUT
IN
=+
=
=+
=−
=
+
( )
22
3
2
2
η
∆
∆
III
CRMS PRMS AVGin
=−
22
∆IVV V
Vf L
DV
V
LIN OUT OUT
IN SW
OUT
IN
=−×
××
=
()
ESR V
II
CIDD
Vf
IN ESR
OUT L
IN OUT
QSW
=
+
=×−
×
∆
∆
∆
2
1()
0
100
200
300
400
500
600
700
800
-40 10025 125 150
TEMPERATURE (°C)
VF_D1 (mV)
Figure 3. Forward-Voltage Drop vs. Temperature of the Internal
Body Diode of MAX5090
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
______________________________________________________________________________________ 13
MAX5090A/B/C
In a dynamic load application, the allowable deviation
of the output voltage during the fast transient load dic-
tates the output capacitance value and the ESR. The
output capacitors supply the step-load current until the
controller responds with a greater duty cycle. The
response time (tRESPONSE) depends on the closed-
loop bandwidth of the converter. The resistive drop
across the capacitor ESR and capacitor discharge
cause a voltage droop during a step-load. Use a com-
bination of low-ESR tantalum and ceramic capacitors
for better transient load and ripple/noise performance.
Use the following equations to calculate the deviation of
output voltage due to the ESR and capacitance value
of the output capacitor:
where ISTEP is the load step and tRESPONSE is the
response time of the controller. Controller response
time is approximately one-third of the reciprocal of the
closed-loop unity-gain bandwidth, 20kHz typically.
Board Layout Guidelines
1) Minimize ground noise by connecting the anode of
the Schottky rectifier, the input bypass capacitor
ground lead, and the output filter capacitor ground
lead to a large PGND plane.
2) Minimize lead lengths to reduce stray capacitance,
trace resistance, and radiated noise. In particular,
place the Schottky rectifier diode right next to the
device. Also, place the BST and VD bypass capaci-
tors very close to the device.
3) Connect the exposed pad of the IC to the SGND
plane. Do not make a direct connection between the
exposed pad plane and SGND (pin 7) under the IC.
Connect the exposed pad and pin 7 to the SGND
plane separately. Connect the ground connection of
the feedback resistive divider, ON/OFF threshold
resistive divider, and the soft-start capacitor to the
SGND plane. Connect the SGND plane and PGND
plane at one point near the input bypass capacitor
at VIN.
4) Use large SGND plane as a heatsink for the
MAX5090. Use large PGND and LX planes as
heatsinks for the rectifier diode and the inductor.
∆
∆
VIxESR
VIxt
C
OESR STEP OUT
OQ
STEP RESPONSE
OUT
=
=
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
14 ______________________________________________________________________________________
Table 2. Typical External Components Selection (Circuit of Figure 4)
VIN (V)
VOUT (V) IOUT (A)
EXTERNAL COMPONENTS
6.5 to 76 3.3 2
MAX5090AATE
CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic
CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata
COUT = 220µF/6.3V 6SVP220MX, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1% (0603)
D1 = PDS5100H, Diodes Inc.
L1 = 47µH, DO5022P-473
7.5 to 76 5 2
MAX5090BATE
CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic
CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1% (0603)
D1 = PDS5100H, Diodes Inc.
L1 = 47µH, DO5022P-473
Application Circuit
PGND
BST
LX
VIN
VIN
SGND
FB
VOUT
R1
VD
L1
CBST
3.3µF
R2
COUT
SS
SYNC
D1
DRAIN
CSS
CIN
CBYPASS
RIN
MAX5090B
ON/OFF
Figure 4. Fixed Output Voltage
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
______________________________________________________________________________________ 15
Table 2. Typical External Components Selection (Circuit of Figure 4) (continued)
VIN (V)
VOUT (V)
IOUT (A)
EXTERNAL COMPONENTS
6.5 to 40 3.3 2
MAX5090AATE
CIN = 330µF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1% (0603)
D1 = B360, Diodes Inc.
L1 = 100µH, DO5022P-104
7.5 to 40 5 2
MAX5090BATE
CIN = 330µF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata
COUT = 100µF/6.3V 6SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 0Ω
R2 = Open
RIN = 10Ω, ±1% (0603)
D1 = B360, Diodes Inc.
L1 = 100µH, DO5022P-104
15 to 40 11 2
MAX5090CATE (VOUT programmed to 11V)
CIN = 330µF/50V EEVFK1H331Q, Panasonic
CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata
COUT = 100µF/16V 16SVP100M, Sanyo
CBST = 0.22µF/16V, GRM188R71C224K, Murata
R1 = 910kΩ
R2 = 100kΩ
R3 = 88.2kΩ, ±1% (0603)
R4 = 10kΩ, ±1% (0603)
RIN = 10Ω, ±1% (0603)
D1 = B360, Diodes Inc.
L1 = 100µH, DO5022P-104
Table 3. Component Suppliers
SUPPLIER WEBSITE
AVX www.avxcorp.com
Coilcraft www.coilcraft.com
Diodes Incorporated www.diodes.com
Panasonic www.panasonic.com
Sanyo www.sanyo.com
TDK www.component.tdk.com
Vishay www.vishay.com
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
16 ______________________________________________________________________________________
Chip Information
PROCESS: BCD
TRANSISTOR COUNT: 7893
PART
TEMP RANGE
PIN-
PACKAGE*
OUTPUT
VOLTAGE
(V)
MAX5090CATE+
-40°C to +125°C 16 TQFN-EP**
Adj
MAX5090CATE
-40°C to +125°C 16 TQFN-EP**
Adj
Ordering Information (continued)
*The package code is T1655-3.
**EP = Exposed pad.
+Denotes lead-free package.
Figure 5. Load-Temperature Monitoring with ON/OFF (Requires Accurate VIN)
PGND
BST
LX
VIN
SGND
FB
VOUT
5V, 2A
Rt C
t
VD
CBST
100µH
3.3µF
COUT
100µF
SS
SYNC
D1
B360
DRAIN
*LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENT AS POSSIBLE.
CSS
CIN
68µF
CBYPASS
RIN
VIN
12V
MAX5090B
PTC
ON/OFF
MAX5090A/B/C
2A, 76V, High-Efficiency MAXPower Step-Down
DC-DC Converters
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
©2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Heslington
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
QFN THIN.EPS