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MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
General Description
Benefits and Features
The MAX25232 is a small, synchronous buck converter
with integrated high-side and low-side switches. The device is designed to deliver up to 3A with 3.5V to 36V input
voltages while using only 3.5µA quiescent current at no
load.
● Synchronous DC-DC Converter with Integrated FETs
• MAX25232ATCA/ATCB/ATCG/ATCH = 2.5A IOUT
• MAX25232ATCD/ATCE/ATCF = 3A IOUT
• 3.5μA Quiescent Current in Standby Mode
The device provides an accurate output voltage of ±2%
in FPWM mode within the normal 6V to 18V operation input range. With 65ns minimum on-time capability, the converter is capable of large input-to-output conversion ratios. Voltage quality can be monitored by observing the
PGOOD signal. The device can operate in dropout by running at 99% duty cycle, making it ideal for automotive and
industrial applications. The IC comes in fixed output voltage and adjustable output voltage (MAX25232ATCF and
MAX25232ATCG only) options. For MAX25232ATCF and
MAX25232ATCG, output voltage can be set between 3V
and 10V using an external resistor-divider. Frequency is
internally fixed at 2.1MHz, which allows for small external
components and reduced output ripple, and guarantees
no AM interference. A 400kHz option is also offered to provide minimum switching losses and maximum efficiency.
The device automatically enters skip mode at light loads
with ultra-low 3.5µA quiescent current at no load. The device offers pin-enabled spread-spectrum-frequency modulation designed to minimize EMI-radiated emissions due
to the modulation frequency.
The MAX25232 variants are available in a small (3mm x
3mm) 12-pin TDFN package with an exposed pad, and requires very few external components.
Applications
● Automotive
● Industrial
● High-Voltage DC-DC Converters
19-100723; Rev 3; 4/21
● Small Solution Size Saves Space
• 65ns Minimum On-Time
• 2.1MHz or 400kHz Operating Frequency
• Fixed 5V/3.3V Output Voltage with ±2% Output
Accuracy in FPWM Mode (5V/3.3V)
• Other Fixed VOUT Options Between 3V - 5.5V (in
50mV steps) Available for Precise Output Voltage
Setting
• External Resistor Divider Options to Adjust the
Output Voltage Between 3V and 10V
• Fixed 3.5ms Internal Soft-Start
• Innovative Current-Mode-Control Architecture
Minimizes Total Board Space and BOM Count
● PGOOD Output and High-Voltage EN Input Simplify
Power Sequencing
● Protection Features and Operating Range Ideal for
Automotive Applications
• 3.5V to 36V Operating VIN Range
• 40V Load-Dump Protection
• 99% Duty-Cycle Operation with Low Dropout
• -40°C to +125°C Automotive Temperature Range
• AEC-Q100 Qualified
Ordering Information appears at end of data sheet.
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Simplified Block Diagram
SPS
SYNC
MAX25232
HVLDO
EN
REF
BANDGAP
OSC
BST
BIAS
SUP
CLK
CURRENT SENSE
+
SOFTSTART
SLOPE COMP
LOGIC
OUT
CONTROL
PWM
BIAS
LX
EAMP
FB
FB
SW1
V/RESET
COMP
SW2
GND
MAX25232ATCF
MAX25232ATCG
PGOOD
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Maxim Integrated | 2
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Absolute Maximum Ratings
SUP ........................................................................ -0.3V to +40V
EN........................................................................... -0.3V to +40V
BST to LX (Note 1) ................................................................. +6V
BST......................................................................... -0.3V to +45V
FB ...............................................................-0.3V to VBIAS + 0.3V
SYNC..........................................................-0.3V to VBIAS + 0.3V
SPS ............................................................-0.3V to VBIAS + 0.3V
OUT ........................................................................ -0.3V to +18V
PGOOD .................................................................... -0.3V to +6V
PGND to AGND..................................................... -0.3V to +0.3V
BIAS....................................................................... -0.3V to +6.0V
LX Continuous RMS Current ....................................................3A
OUT Short-Circuit Duration...........................................................
ESD Protection Human Body Model.....................................±2kV
Continuous Power Dissipation (TA = +70°C) 12-pin SWTDFN
(derate 24.4mW/°C above +70°C) ..................................1951mW
Storage Temperature Range .............................. -65ºC to +150ºC
Operating Junction Temperature (Note 6) ..........-40ºC to +150ºC
Lead Temperature (Soldering, 10s) .................................. +300ºC
Soldering Temperature (Reflow)....................................... +260ºC
Note 1: LX has internal clamp diodes to PGND/AGND and SUP. Applications that forward bias these diodes should take care not to
exceed the IC’s package power-dissipation limits.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent 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 maximum rating conditions for
extended periods may affect device reliability.
Package Information
12 TDFN
Package Code
TD1233+2C
Outline Number
21-0664
Land Pattern Number
90-0397
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction-to-Ambient (θJA)
41°C/W
Junction-to-Case Thermal Resistance (θJC)
9°C/W
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages.
Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different
suffix character, but the drawing pertains to the package regardless of RoHS status.
Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a
four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/
thermal-tutorial.
Electrical Characteristics
(VSUP = VEN, VSUP = 14V, VSYNC = 0V, VOUT = 5V, TJ = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
PARAMETER
Supply Voltage Range
SYMBOL
VSUP
CONDITIONS
After Start-Up
MIN
TYP
36
3
36
t < 1s
Supply Current
ISUP
MAX25232ATCA,
MAX25232ATCD,
MAX25232ATCH
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UNITS
V
40
VEN = low
MAX25232ATCB,
MAX25232ATCE
MAX
3.5
1
5
No load, no
switching
3.5
8
No load (Note 3)
4.5
No load, no
switching
No load (Note 3)
6
µA
10
7.5
Maxim Integrated | 3
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Electrical Characteristics (continued)
(VSUP = VEN, VSUP = 14V, VSYNC = 0V, VOUT = 5V, TJ = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
PARAMETER
LX Leakage
SYMBOL
ILX,LEAK
Undervoltage Lockout
UVLO
BIAS Voltage
VBIAS
CONDITIONS
VSUP = 40V, LX = 0 or 40V, TA = +25°C
VBIAS rising
MIN
TYP
MAX
UNITS
+1
µA
2.73
2.93
-1
2.53
Hysteresis
0.13
5.5V ≤ VSUP ≤ 36V, PWM mode
5
V
V
BUCK CONVERTER
Skip mode (Note 3)
4.85
4.99
5.1
Fixed-frequency
PWM mode
4.93
5
5.07
Skip mode (Note 3)
3.2
3.3
3.37
Fixed-frequency
PWM mode
3.25
3.3
3.35
Skip Mode (Note 3)
3.88
4
4.12
Fixed-frequency
PWM mode
3.92
4
4.08
VOUT,5V
MAX25232ATCA,
MAX25232ATCD
VOUT,3.3V
MAX25232ATCB,
MAX25232ATCE
Voltage Accuracy, 4V
VOUT,4V
MAX25232ATCH
Output Voltage Range
VOUT
MAX25232ATCF, MAX25232ATCG
3
FB Voltage Accuracy
VFB
MAX25232ATCF, MAX25232ATCG
0.985
IFB
MAX25232ATCF,
MAX25232ATCG
VFB = 1V, TA =
+25°C
0.02
µA
MAX25232ATCF,
MAX25232ATCG
VSUP = 6V to 36V
0.02
%/V
Voltage Accuracy, 5V
Voltage Accuracy, 3.3V
FB Current
FB Line Regulation
1
V
10
V
1.015
V
High-Side Switch OnResistance
RON,HS
VBIAS = 5V, ILX = 1A
70
mΩ
Low-Side Switch OnResistance
RON,LS
VBIAS = 5V, ILX = 1A
70
mΩ
High-Side Current-Limit
Threshold
ILIM
Low-Side Negative
Current-Limit Threshold
INEG
Soft-Start Ramp Time
(Note 4)
ISS
Minimum On-Time
tON
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
3.05
3.50
3.95
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
4.10
4.70
5.60
-1.2
fSW
Spread-Spectrum
Range
SS
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A
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
3.5
5
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
5.5
7.5
ms
(Note 3)
65
ns
98
99
%
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
1.925
2.1
2.275
MHz
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
360
400
440
kHz
Maximum Duty Cycle
PWM Switching
Frequency
A
VSPS = 5V
±3
%
Maxim Integrated | 4
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Electrical Characteristics (continued)
(VSUP = VEN, VSUP = 14V, VSYNC = 0V, VOUT = 5V, TJ = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
PGOOD
PGOOD Threshold,
Rising
VTHR,PGD
VOUT rising
91
93
95
%
PGOOD Threshold,
Falling
VTHF,PGD
VOUT falling
90
92
94
%
PGOOD Debounce
Time
tDEB
MAX25232ATCA,
MAX25232ATCB,
MAX25232ATCG,
MAX25232ATCH
PWM mode
60
Skip mode
90
MAX25232ATCD,
MAX25232ATCE,
MAX25232ATCF
PWM mode
80
Skip mode
110
µs
PGOOD High-Leakage
Current
ILEAK,PGD
TA = +25°C
1
µA
PGOOD Low Level
VOUT,PGD
Sinking 1mA
0.4
V
LOGIC LEVELS
EN Level, High
VIH,EN
EN Level, Low
VIL,EN
EN Input Current
IIN,EN
External Input Clock
Frequency
SYNC Threshold, High
SYNC Threshold, Low
SYNC Internal Pulldown
FSYNC
2.4
V
VEN = VSUP = 14V, TA = +25°C
2.6
MHz
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
325
500
kHz
1.4
V
VIL,SYNC
VIH,SPS
VIL,SPS
µA
1.7
0.4
RPD,MODE
SPS Threshold, Low
V
1
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
VIH,SYNC
SPS Threshold, High
0.6
1000
1.4
V
0.4
SPS Internal Pulldown
V
kΩ
V
1000
kΩ
THERMAL PROTECTION
Thermal Shutdown
TSHDN
(Note 3)
175
°C
Thermal-Shutdown
Hysteresis
TSHDN.HYS
(Note 3)
15
°C
Note 2: Limits are 100% tested at TA = +25°C. Limits over the operating temperature range and relevant supply voltage are guaranteed
by design and characterization. Typical values are at TA = +25°C.
Note 3: Guaranteed by design; not production tested.
Note 4: Soft-start time is measured as the time taken from EN going high to PGOOD going high.
Note 5: The device is designed for continuous operation up to TJ = +125°C for 95,000 hours and TJ = +150°C for 5,000 hours.
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Maxim Integrated | 5
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Operating Characteristics
(VSUP = VEN = +14V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD
(fSW= 2.1MHz)
100
toc01
100
5V
90
90
3.3V
5V
50
40
FPWM
30
20
3.3V
60
5V
50
0.01
0.1
1
0.001
0.01
0.1
0
1
LOAD CURRENT (A)
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
(5VOUT, 2.1MHz)
500
VEN = 0V
5V, 2.1MHz
300
250
3.3V, 2.1MHz
100
3.3V, 400kHz
0
36
0.0
0.2
2.0
1.5
OUTPUT-VOLTAGE CHANGE (%)
OUTPUT-VOLTAGE CHANGE (%)
1.0
FPWM
0.0
SKIP
-0.5
-1.0
FPWM
0.0
SKIP
-0.5
-1.0
-2.0
1.0
6
16
-0.5
-1.0
-2.0
0.0
36
FPWM
SKIP
-1.5
26
2.0
1.5
0.0
-2.0
36
LOAD REGULATION
(5VOUT, 400kHz)
toc08
1.0
0.5
26
VIN (V)
VIN = 14V
-1.5
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0.8
2.0
1.5
VIN (V)
0.6
LOAD REGULATION
(5VOUT, 2.1MHz)
toc07
1A LOAD
16
0.4
OUTPUT-VOLTAGE CHANGE (%)
LINE REGULATION
(5VOUT, 400kHz)
6
0.5
ILOAD(mA)
VIN (V)
0.5
1.0
-1.5
50
26
toc06
2.0
OUTPUT-VOLTAGE CHANGE (%)
ISUP (µA)
IQ(µA)
350
150
16
36
1.5
5V, 400kHz
200
6
26
1A LOAD
400
0.1
16
LINE REGULATION
(5VOUT, 2.1MHz)
toc05
450
1
3.3VOUT, 2.1MHz
6
VIN (V)
STANDBY CURRENT
vs. LOAD CURRENT
toc04
3.3VOUT, 400kHz
5
VIN = 14V
L = 10µH
LOAD CURRENT (A)
10
5VOUT, 400kHz
5VOUT, 2.1MHz
FPWM
10
0
15
10
40
20
VIN = 14V
L = 2.2 µH
10
toc03
25
NO LOAD
5V
70
30
20
0.001
toc02
3.3V
SKIP
IQ (µA)
3.3V
60
0
QUIESCENT SUPPLY CURRENT
vs. INPUT VOLTAGE
(SKIP MODE)
80
SKIP
70
EFFICIENCY (%)
80
EFFICIENCY (%)
EFFICIENCY vs. LOAD
(fSW= 400kHz)
toc09
VIN = 14V
1.0
0.5
0.0
SKIP
FPWM
-0.5
-1.0
-1.5
0.5
1.0
1.5
IOUT(A)
2.0
2.5
-2.0
0.0
0.5
1.0
1.5
2.0
2.5
IOUT(A)
Maxim Integrated | 6
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Operating Characteristics (continued)
(VSUP = VEN = +14V, TA = +25°C, unless otherwise noted.)
SHUTDOWN WAVEFORM
(5VOUT, 2.1MHz, 2.5A LOAD)
STARTUP WAVEFORM
(5VOUT, 2.1MHz)
toc10
VEN
STEADY
-STATE SWITCHING WAVEFORM
(5VOUT, 2.1MHz, NO LOAD
toc11
5V/div
toc12
VEN
5V/div
7V/div
VLX
5V/div
IINDUCTOR
VPGOOD
2A/div
VPGOOD
5V/div
VOUT
200mA/div
IINDUCTOR
5V/div
5V/div
VOUT
VOUT
5V/div
1ms/div
SLOW IV
N RAMP
(5VOUT, 2.1MHz)
200ns/div
100µs/div
UNDERVOLTAGE PULSE
(5VOUT, 2.1MHz)
SHORT
-CIRCUIT RESPONSE
(5VOUT, 2.1MHz)
toc13
toc14
10mA Load
toc15
VOUT
5V/div
VIN
5V/div
5V/div
VOUT
5V/div
VBIAS
5V/div
VPGOOD
5V/div
VPGOOD
VIN
5V/div
VBIAS
VOUT
2V/div
VPGOOD
5V/div
5V/div
IINDUCTOR
1A/div
5µs/div
10ms/div
5s/div
LOAD-DUMP TEST
(5VOUT, 2.1MHz)
SPECTRAL
-ENERGY DENSITY
vs. FREQUENCY
(5VOUT, 2.1MHz)
LOAD-TRANSIENT RESPONSE
(5VOUT, 2.1MHz)
toc16
toc17
0
VIN
10V/div
VOUT
1A/div
ILOAD
5V/div
100mV/div
(ACCOUPLED)
VOUT
5V/div
VBIAS
OUTPUT SPECTRUM (dBm)
-10
toc19
VSPS= 5V
-20
-30
-40
-50
-60
-70
-80
100ms/div
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20µs/div
-90
1.85
1.95
2.05
2.15
2.25
2.35
FREQUENCY (MHz)
Maxim Integrated | 7
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Operating Characteristics (continued)
(VSUP = VEN = +14V, TA = +25°C, unless otherwise noted.)
SHORT
-CIRCUIT RESPONSE
(3.3VOUT, 400kHz)
toc19
VOUT
5V/div
VPGOOD
5V/div
VBIAS
5V/div
2A/div
IINDUCTOR
10µs/div
Pin Configuration
AGND
7
FB
8
OUT
9
BIAS
SYNC
11
10
PGOOD
12
MAX25232
3
4
5
6
SUP
LX
PGND
2
EN
BST
1
SPS
MAX25232
TDFN-EP
(3mm x 3mm)
Pin Description
PIN
NAME
1
SPS
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FUNCTION
Spread-Spectrum Enable. Connect logic-high to enable spread spectrum of internal oscillator, or
logic-low to disable spread spectrum. This pin has a 1MΩ internal pulldown.
Maxim Integrated | 8
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Pin Description (continued)
PIN
NAME
FUNCTION
2
EN
High-Voltage-Compatible Enable Input. If this pin is low, the part is off.
3
BST
Bootstrap Pin for HS Driver. It is recommended to use 0.1μF from BST to LX.
4
SUP
Supply Input. Connect a 4.7μF ceramic capacitor from SUP to PGND.
5
LX
6
PGND
Power Ground. Ground return path for all high-current/high-frequency noisy signals.
7
AGND
Analog Ground. Ground return path for all ‘quiet’ signals.
8
FB
Buck Switching Node. Connect inductor between LX and OUT. See the Inductor Selection section.
If the part is off, this node is high impedance.
Connect this pin to BIAS for fixed output voltage options. For MAX25232ATCF and
MAX25232ATCG, use it as a FB pin to set the output voltage.
9
OUT
Buck Regulator Output-Voltage-Sense Input. Bypass OUT to PGND with ceramic capacitors.
10
BIAS
5V Internal Bias Supply. Connect a 1μF (min) ceramic capacitor to AGND.
11
SYNC
Sync Input. If connected to ground or open, skip-mode operation is enabled under light loads; if
connected to BIAS, forced-PWM mode is enabled. This pin has a 1MΩ internal pulldown.
12
PGOOD
-
EP
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Open-Drain Reset Output. External pullup required.
Exposed Pad. EP must be connected to ground plane on PCB, but is not a current-carrying path
and is only needed for thermal transfer.
Maxim Integrated | 9
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Detailed Description
The MAX25232 family of small, current-mode-controlled buck converters features synchronous rectification and requires
no external compensation network. The devices are designed for 3A output current and can stay in dropout by running
at 99% duty cycle. Each device provides an accurate output voltage of ±2% in FPWM mode within the 6V to 18V
input range. Voltage quality can be monitored by observing the PGOOD signal. The devices operate at 2.1MHz (typ)
frequency, which allows for small external components, reduced output ripple, and guarantees no AM band interference.
The devices are also available at 400kHz (typ) for minimum switching losses and maximum efficiency.
Each device features an ultra-low 3.5μA (typ) quiescent supply current in standby mode. The device enters standby
mode automatically at light loads if the high-side FET (HSFET) does not turn on for eight consecutive clock cycles.
The devices operate from a 3.5V to 36V supply voltage and can tolerate transients up to 40V, making them ideal for
automotive applications. The devices are available in factory-trimmed output voltages (5V, 3.3V). MAX25232ATCF and
MAX25232ATCG configuration can be used to program output voltage between 3V and 10V using an external resistordivider. For fixed-output voltages outside of 3.3V and 5V, contact factory for availability.
Enable Input (EN)
Each device is activated by driving EN high. EN is compatible from a 3.3V logic level to automotive battery levels. EN
can be controlled by microcontrollers and automotive KEY or CAN inhibit signals. The EN input has no internal pullup/
pulldown current to minimize the overall quiescent supply current. To realize a programmable undervoltage-lockout level,
use a resistor-divider from SUP to EN to AGND.
Bias/UVLO
Each device features undervoltage lockout. When the device is enabled, an internal bias generator turns on. LX begins
switching after VBIAS has exceeded the internal undervoltage-lockout level, VUVLO = 2.73V (typ).
Soft-Start
Each device features an internal soft-start timer. The output voltage soft-start time is 3.5ms (typ), which includes the delay
in PGOOD. If a short circuit or undervoltage is encountered after the soft-start timer has expired, the device is disabled
for 7ms (typ) and then reattempts soft-start again. This pattern repeats until the short circuit has been removed.
Oscillator/Synchronization and Efficiency (SYNC)
Each device has an on-chip oscillator that provides a 2.1MHz (typ) or 400kHz (typ) switching frequency. There are two
operation modes, depending on the condition of SYNC. If SYNC is unconnected or at AGND, the device operates in
highly efficient pulse-skipping mode. If SYNC is connected to BIAS or has a clock applied to it, the device is in forcedPWM mode (FPWM). The device can be switched during operation between FPWM mode and skip mode by switching
SYNC.
Skip-Mode Operation
The devices enter skip mode when the SYNC pin is connected to ground or is unconnected and the peak load current
is < 600mA (typ). In this mode, the HSFET is turned on until the inductor current ramps up to 600mA (typ) peak value
and the internal feedback voltage is above the regulation voltage (1.0V, typ). At this point, both the HSFETs and low-side
FETs (LSFETs) are turned off. Depending on the choice of the output capacitor and the load current, the HSFET turns
on when OUT (valley) drops below the 1.0V (typ) feedback voltage. When the device is in skip mode, the internal highvoltage LDO is turned off to save current. VBIAS is supplied by the output after the soft start is completed.
Achieving High Efficiency at Light Loads
Each device operates with very low-quiescent current at light loads to enhance efficiency and conserve battery life. When
the device enters skip mode, the output current is monitored to adjust the quiescent current. The lowest quiescent-current
standby mode is only available for factory-trimmed devices between 3.0V and 5.5V output voltages. When the output
current is < approximately 5mA, the device operates in the lowest quiescent-current mode, also called standby mode. In
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Maxim Integrated | 10
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
this mode, the majority of the internal circuitry (excluding that necessary to maintain regulation) in the device is turned off
to save current. Under no load and with skip mode enabled, the device typically draws 3.5μA for the 3.3V parts, and 6μA
for the 5.0V parts. For load currents > 5mA, the device enters normal skip mode and still maintains very high efficiency.
Output-Voltage Overshoot Protection
In dropout, the output voltage closely follows the input voltage, but is below the regulation point. The device runs at
maximum duty cycle to satisfy the loop, and the internal error-amplifier output is railed high. When the input voltage rises
above the output, the device comes out of dropout, but the internal error-amplifier output takes some time to get back to
steady state. This causes an overshoot in the output voltage. To limit this overshoot, the device clamps the output of the
error amplifier while coming out of dropout, causing it to discharge faster and limiting the output-voltage overshoot. The
actual value of the overshoot depends on the output capacitor, inductor, and load.
Controlled EMI with Forced-Fixed Frequency
In FPWM mode, the device attempts to operate at a constant switching frequency for all load currents. For tightest
frequency control, apply the operating frequency to SYNC. The advantage of FPWM is a constant switching frequency,
which improves EMI performance; the disadvantage is that considerable current can be thrown away. If the load current
during a switching cycle is less than the current flowing through the inductor, the excess current is diverted to AGND.
Extended Input Voltage Range
In some cases, the device is forced to deviate from its operating frequency, independent of the state of SYNC. At high
input voltages above 18V (especially for 2.1MHz operation), the required on-time to regulate its output voltage may be
smaller than the minimum on-time (65ns, typ). In this event, the device is forced to lower its switching frequency by
skipping pulses. If the input voltage is reduced and the device approaches dropout, it continuously tries to turn on the
HSFET. To maintain gate charge on the HSFET, the BST capacitor must be periodically recharged. To ensure proper
charge on the BST capacitor when in dropout, the HSFET is turned off every 20μs and the LSFET is turned on for
approximately 200ns. This gives an effective duty cycle of > 99%, and a switching frequency of 50kHz when in dropout.
Spread-Spectrum Option
Each device has an optional spread spectrum enabled by the SPS pin. If SPS is pulled high, the internal operating
frequency varies by ±3% relative to the internally generated 2.1MHz (typ) operating frequency. Spread spectrum is
offered to improve EMI performance of the device. The internal spread spectrum does not interfere with the external clock
applied on the SYNC pin. It is active only when the device is running with an internally generated switching frequency.
Power-Good (PGOOD)
Each device features an open-drain power-good output. PGOOD is an active-high output that pulls low when the output
voltage is below 92% (typ) of its nominal value. PGOOD is high impedance when the output voltage is above 93% (typ)
of its nominal value. Connect a 20kΩ (typ) pullup resistor to an external supply, or to the on-chip BIAS output.
Overcurrent Protection
Each device limits the peak output current to 3.5A (typ) for 2.1MHz switching frequency parts and 4.7A (typ) for the
400kHz switching frequency parts. The accuracy of the current limit is ±12%, making selection of external components
very easy. To protect against short-circuit events, the device shuts off when OUT is below 50% of VOUT and an
overcurrent event is detected. The device attempts a soft-start restart every 7ms and stays off if the short circuit has not
been removed. When the current limit is no longer present, it reaches the output voltage by following the normal soft-start
sequence. If the device’s die reaches the thermal limit of 175°C (typ) during the current-limit event, it immediately shuts
off.
Thermal-Overload Protection
Each device features thermal-overload protection. The device turns off when the junction temperature exceeds +175°C
(typ). Once the device cools by 15°C (typ), it turns back on with a soft-start sequence.
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Maxim Integrated | 11
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Applications Information
Setting the Output Voltage
MAX25232 comes with fixed VOUT options (set internally) of 5V and 3.3V. For setting the output voltage between 3V
- 10V externally using resistor-dividers, chose MAX25232ATCF and MAX25232ATCG. Connect a resistor-divider from
output (OUT) to FB to AGND (see Figure 1). Select RFB2 (FB to AGND resistor) ≤ 500kΩ. Calculate RFB1 (OUT to FB
resistor) with the following equation:
RFB1 = RFB2
[ ] ]
VOUT
VFB
−1
where VFB = 1V (see Electrical Characteristics).
Other fixed-output voltage options (set internally) between 3V - 5.5V in 50mV steps are also available. Contact the factory
if your application requires fixed output voltage in this range.
VOUT
RFB1
MAX25232ATCF
MAX25232ATCG
FB
RFB2
Figure 1. Setting the Output Voltage with External Resistor-Dividers
Input Capacitor
A 4.7μF low-ESR ceramic input capacitor is recommended for proper device operation. This value can be adjusted based
on application input-voltage-ripple requirements.
The discontinuous input current of the buck converter causes large input-ripple current. Switching frequency, peak
inductor current, and the allowable peak-to-peak input-voltage ripple dictate the input-capacitance requirement.
Increasing the switching frequency or the inductor value lowers the peak-to-average current ratio, yielding a lower inputcapacitance requirement. The input ripple is mainly comprised of ΔVQ (caused by the capacitor discharge) and ΔVESR
(caused by the ESR of the input capacitor). The total voltage ripple is the sum of ΔVQ and ΔVESR. Assume that inputvoltage ripple from the ESR and the capacitor discharge is equal to 50% each. The following equations show the ESR
and capacitor requirement for a target voltage ripple at the input:
Equation 1:
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Maxim Integrated | 12
MAX25232
ESR =
36V, 3A Mini Buck Converters with 3.5μA IQ
∆ VESR
/
IOUT + ( ∆ IP − P 2)
IOUT × D(1 − D)
CIN = ∆ V × × f
Q
SW
where:
∆ IP − P =
(VIN − VOUT) × VOUT
VIN × fSW × L
and:
VOUT
D= V
IN
where IOUT is the output current, D is the duty cycle, and fSW is the switching frequency. Use additional input capacitance
at lower input voltages to avoid possible undershoot below the UVLO threshold during transient loading.
Inductor Selection
See Table 1 for inductor selection. The nominal standard value selected should be within ±50% of the specified
inductance. The specified values applies to all output voltage settings.
Table 1. Inductor Selection
PART
INDUCTANCE (µH)
For fSW = 2.1MHz
2.2
10
For fSW = 400kHz
Output Capacitor
For optimal phase margin (> 60 degrees, typ), the recommended output capacitances are shown in Table 2.
Recommended values are the actual capacitances after voltage derating is taken into account.
If a lower output capacitance is required, contact the factory for recommendations. Additional output capacitance may
be needed based on application-specific output-voltage-ripple requirements. The specified values applies to all output
voltage settings.
Table 2. Output-Capacitance Selection
PART
OUTPUT CAPACITANCE (µF)
For fSW = 2.1MHz
30
For fSW = 400kHz
44
The allowable output-voltage ripple and the maximum deviation of the output voltage during step-load currents determine
the output capacitance and its ESR. The output ripple comprises ΔVQ (caused by the capacitor discharge) and ΔVESR
(caused by the ESR of the output capacitor). Use low-ESR ceramic or aluminum electrolytic capacitors at the output.
For aluminum electrolytic capacitors, the entire output ripple is contributed by ΔVESR. Use Equation 2 to calculate the
ESR requirement and choose the capacitor accordingly. If using ceramic capacitors, assume the contribution to the
output ripple voltage from the ESR and the capacitor discharge to be equal. The following equations show the output
capacitance and ESR requirement for a specified output-voltage ripple.
Equation 2:
∆ VESR
ESR = ∆ I
P−P
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Maxim Integrated | 13
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
∆ IP − P
COUT = 8 × ∆ V × f
Q SW
where:
∆ IP − P =
(VIN − VOUT) × VOUT
VIN × fSW × L
and:
VOUT_RIPPLE = ∆ VESR + ∆ VQ
ΔIP-P is the peak-to-peak inductor current as calculated above, and fSW is the converter’s switching frequency. The
allowable deviation of the output voltage during fast transient loads also determines the output capacitance and its ESR.
The output capacitor supplies the step-load current until the converter responds with a greater duty cycle. The resistive
drop across the output capacitor’s ESR and the capacitor discharge causes a voltage droop during a step load. Use a
combination of low-ESR tantalum and ceramic capacitors for better transient-load and ripple/noise performance. Keep
the maximum output-voltage deviations below the tolerable limits of the electronics being powered. When using a ceramic
capacitor, assume an 80% and 20% contribution from the output-capacitance discharge and the ESR drop, respectively.
Use the following equations to calculate the required ESR and capacitance value:
Equation 3:
∆ VESR
ESROUT = I
STEP
L
COUT ≥ ISTEP2 × 2 × (V
SUP − VOUT) × DMAX × ∆ VQ
tDELAY
+ ISTEP × ∆ V
Q
where ISTEP is the load step and tDELAY is the delay for the PWM mode, the worst-case delay would be (1-D) tSW when
the load step occurs right after a turn-on cycle. This delay is higher in skip mode.
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching power losses and clean, stable operation. Use a multilayer board
whenever possible for better noise immunity. Follow the guidelines below for a good PCB layout:
1. Place the input capacitor (CIN) close to the device to reduce the input AC-current loop. AC current flows on the loop
formed by the input capacitor and the half-bridge MOSFETs internal to the device (see Figure 2). A small loop would
reduce the radiating effect of high switching currents and improve EMI functionality.
2. Solder the exposed pad to a large copper-plane area under the device. To effectively use this copper area as heat
exchanger between the PCB and ambient, expose the copper area on the top and bottom side. Add a few small vias
or one large via on the copper pad for efficient heat transfer.
3. Connect PGND and AGND pins directly to the exposed pad under the IC. This ensures the shortest connection path
between AGND and PGND.
4. Keep the power traces and load connections short. This practice is essential for high efficiency. Use thick copper
PCB to enhance full-load efficiency and power-dissipation capability.
5. Using internal PCB layers as ground plane helps to improve the EMI functionality as ground planes act as a shield
against radiated noise. Have multiple vias spread around the board, especially near the ground connections to have
better overall ground connection.
6. Keep the bias capacitor (CBIAS) close to the device to reduce the bias current loop. This helps to reduce noise on the
bias for smoother operation.
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Maxim Integrated | 14
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
GROUND
SUP
MAX25232
LX
CBIAS
CIN
AC current
loop
GROUND
VIAS
GROUND
COUT
OUT
COUT
COUT
INDUCTOR
GROUND
VCC
Figure 2. Recommended PCB Layout for MAX25232
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Maxim Integrated | 15
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Application Circuits
Circuit 1
MAX25232
SUP
BST
CIN
4.7µF
LX
CBST
0.1µF
L
2.2µH
NH
OUT
SYNC
FB
EN
PGOOD
SPS
COUT
30µF
NL
BIAS
AGND
PGND
CBIAS
1µF
Figure 3. 2.1MHz, 5V/3.3V Fixed Output Voltage Configuration in 12-Pin TDFN Package
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Maxim Integrated | 16
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Application Circuits (continued)
Circuit 2
MAX25232
SUP
BST
CIN
4.7µF
LX
CBST
0.1µF
L
10µH
NH
OUT
SYNC
FB
EN
PGOOD
SPS
COUT
44µF
NL
BIAS
AGND
PGND
CBIAS
1µF
Figure 4. 400kHz, 5V/3.3V Fixed Output Voltage Configuration in 12-Pin TDFN Package
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Maxim Integrated | 17
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Typical Application Circuits (continued)
Circuit 3
MAX25232
SUP
BST
CIN
4.7µF
CBST
0.1µF
L
10µH
LX
NH
OUT
SYNC
NL
RFB1
EN
FB
PGOOD
SPS
COUT
44µF
BIAS
AGND
PGND
RFB2
CBIAS
1µF
Figure 5. 400kHz, External Resistor-Divider Configuration in 12-Pin TDFN Package
Ordering Information
PART
TEMP RANGE
PINPACKAGE
IOUT
(A)
DESCRIPTION
MAX25232ATCA/V+
-40°C to +125°C
12 TDFN
2.1MHz, Fixed 5V output
2.5
MAX25232ATCB/V+
-40°C to +125°C
12 TDFN
2.1MHz, Fixed 3.3V output
2.5
MAX25232ATCD/V+
-40°C to +125°C
12 TDFN
400kHz, Fixed 5V output
3
MAX25232ATCE/V+
-40°C to +125°C
12 TDFN
400kHz, Fixed 3.3V output
3
MAX25232ATCF/V+
-40°C to +125°C
12 TDFN
400kHz, Adjustable Output Voltage Between 3V
and 10V
3
MAX25232ATCG/V+
-40°C to +125°C
12 TDFN
2.1MHz, Adjustable Output Voltage Between 3V
and 10V
2.5
MAX25232ATCH/V+
-40°C to +125°C
12 TDFN
2.1MHz, Fixed 4V output
2.5
Note: All parts are OTP versions, no metal mask differences.
/V Denotes an automotive-qualified part.
+ Denotes a lead(Pb)-free/RoHS-compliant package
* Future product - contact factory for availability
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Maxim Integrated | 18
MAX25232
36V, 3A Mini Buck Converters with 3.5μA IQ
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
0
7/20
Initial release
1
10/20
Updated Benefits and Features, Electrical Characteristics, Pin Configuration, Pin
Description, Applications Information, and Ordering Information
2
3/21
Updated Absolute Maximum Ratings, Electrical Characteristics, and Ordering
Information
3
4/21
Updated Pin Configuration, Pin Description , Typical Application Circuits
DESCRIPTION
—
1, 4, 5, 9, 10, 14,
20
3, 4, 19
8, 9, 17, 18
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max
limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2021 Maxim Integrated Products, Inc.
