MAX25232ATCA [MAXIM]
36V, 3A Mini Buck Converters with 3.5μA IQ;
| 型号： | MAX25232ATCA |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 36V, 3A Mini Buck Converters with 3.5μA IQ |
| 文件： | 总21页 (文件大小：571K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
General Description
Benefits and Features
The MAX25232 is a small, synchronous buck converter
with integrated high-side and low-side switches. The de-
vice 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 I
OUT
• MAX25232ATCD/ATCE/ATCF = 3A I
OUT
• 3.5μA Quiescent Current in Standby Mode
● Small Solution Size Saves Space
• 65ns Minimum On-Time
The device provides an accurate output voltage of ±2%
in FPWM mode within the normal 6V to 18V operation in-
put range. With 65ns minimum on-time capability, the con-
verter is capable of large input-to-output conversion ra-
tios. Voltage quality can be monitored by observing the
PGOOD signal. The device can operate in dropout by run-
ning at 99% duty cycle, making it ideal for automotive and
industrial applications. The IC comes in fixed output volt-
age 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 pro-
vide 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 de-
vice offers pin-enabled spread-spectrum-frequency mod-
ulation designed to minimize EMI-radiated emissions due
to the modulation frequency.
• 2.1MHz or 400kHz Operating Frequency
• Fixed 5V/3.3V Output Voltage with ±2% Output
Accuracy in FPWM Mode (5V/3.3V)
• Other Fixed V
Options Between 3V - 5.5V (in
OUT
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 V Range
IN
• 40V Load-Dump Protection
• 99% Duty-Cycle Operation with Low Dropout
• -40°C to +125°C Automotive Temperature Range
• AEC-Q100 Qualified
The MAX25232 variants are available in a small (3mm x
3mm) 12-pin TDFN package with an exposed pad, and re-
quires very few external components.
Ordering Information appears at end of data sheet.
Applications
● Automotive
● Industrial
● High-Voltage DC-DC Converters
19-100723; Rev 1; 10/20
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Simplified Block Diagram
SPS SYNC
MAX25232
REF
EN
HVLDO
BANDGAP
OSC
BST
SUP
BIAS
CLK
CURRENT SENSE
SOFTSTART
+
SLOPE COMP
LOGIC
CONTROL
LX
OUT
BIAS
PWM
EAMP
COMP
FB
FB
SW1
V/RESET
SW2
GND
MAX25232ATCF
MAX25232ATCG
PGOOD
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Maxim Integrated | 2
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Absolute Maximum Ratings
SUP ........................................................................ -0.3V to +40V
EN........................................................................... -0.3V to +40V
BST to LX (Note 1) ................................................................. +6V
BST......................................................................... -0.3V to +45V
LX Continuous RMS Current ....................................................3A
OUT Short-Circuit Duration...........................................................
ESD Protection Human Body Model.....................................±2kV
Machine Model....................................................................±200V
FB...............................................................-0.3V to V
SYNC..........................................................-0.3V to V
SPS ............................................................-0.3V to V
OUT........................................................................ -0.3V to +18V
PGOOD .................................................................... -0.3V to +6V
PGND to AGND..................................................... -0.3V to +0.3V
BIAS ...................................................................... -0.3V to +6.0V
+ 0.3V
+ 0.3V
+ 0.3V
Continuous Power Dissipation (T = +70°C) 12-pin SWTDFN
BIAS
BIAS
BIAS
A
(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
21-0664
Outline Number
Land Pattern Number
90-0397
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction-to-Ambient (θ
)
41°C/W
9°C/W
JA
Junction-to-Case Thermal Resistance (θ
)
JC
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
(V
= V , V
= 14V, V
= 0V, V
= 5V, T = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
OUT J
SUP
EN SUP
SYNC
PARAMETER
SYMBOL
CONDITIONS
MIN
3.5
3
TYP
MAX
36
UNITS
Supply Voltage Range
V
SUP
After Start-Up
t < 1s
36
V
40
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Maxim Integrated | 3
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Electrical Characteristics (continued)
(V
= V , V
= 14V, V
= 0V, V
= 5V, T = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
OUT J
SUP
EN SUP
SYNC
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
V
EN
= low
1
5
No load, no
switching
3.5
4.5
6
8
MAX25232ATCB,
MAX25232ATCE
Supply Current
LX Leakage
I
No load (Note 3)
µA
SUP
No load, no
switching
10
MAX25232ATCA,
MAX25232ATCD
No load (Note 3)
7.5
I
V
= 40V, LX = 0 or 40V, T = +25°C
-1
+1
µA
V
LX,LEAK
UVLO
SUP
A
VBIAS rising
Hysteresis
2.53
2.73
0.13
5
2.93
Undervoltage Lockout
BIAS Voltage
V
5.5V ≤ V
≤ 36V, PWM mode
SUP
V
BIAS
BUCK CONVERTER
Skip mode (Note 3)
4.85
4.93
3.2
4.99
5
5.1
MAX25232ATCA,
MAX25232ATCD
Voltage Accuracy, 5V
Voltage Accuracy, 3.3V
Voltage Accuracy, 4V
V
OUT,5V
Fixed-frequency
PWM mode
5.07
3.37
3.35
4.12
4.08
Skip mode (Note 3)
3.3
3.3
4
MAX25232ATCB,
MAX25232ATCE
V
OUT,3.3V
Fixed-frequency
PWM mode
3.25
3.88
3.92
Skip Mode (Note 3)
V
MAX25232ATCH
V
OUT,4V
Fixed-frequency
PWM mode
4
Output Voltage Range
FB Voltage Accuracy
V
MAX25232ATCF, MAX25232ATCG
MAX25232ATCF, MAX25232ATCG
3
10
V
V
OUT
V
0.985
1
1.015
FB
MAX25232ATCF,
MAX25232ATCG
VFB = 1V, TA =
+25°C
FB Current
I
0.02
µA
%/V
mΩ
mΩ
FB
MAX25232ATCF,
MAX25232ATCG
FB Line Regulation
V
SUP
= 6V to 36V
0.02
70
High-Side Switch On-
Resistance
RON,HS
V
= 5V, I = 1A
LX
BIAS
BIAS
Low-Side Switch On-
Resistance
R
V
= 5V, I = 1A
70
ON,LS
LX
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
3.05
4.10
3.50
4.70
-1.2
3.5
3.95
5.60
High-Side Current-Limit
Threshold
I
A
A
LIM
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
Low-Side Negative
Current-Limit Threshold
I
NEG
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
5
Soft-Start Ramp Time
(Note 4)
I
ms
ns
SS
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
5.5
65
7.5
Minimum On-Time
t
(Note 3)
ON
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Maxim Integrated | 4
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Electrical Characteristics (continued)
(V
= V , V
= 14V, V
= 0V, V
= 5V, T = -40°C to +150°C, unless otherwise noted. (Notes 2 and 5))
OUT J
SUP
EN SUP
SYNC
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Maximum Duty Cycle
98
99
%
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
1.925
360
2.1
400
±3
2.275
440
MHz
kHz
%
PWM Switching
Frequency
f
SW
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
Spread-Spectrum
Range
SS
V
SPS
= 5V
PGOOD
PGOOD Threshold,
Rising
V
V
V
rising
falling
91
90
93
95
94
%
%
THR,PGD
OUT
PGOOD Threshold,
Falling
V
92
60
THF,PGD
OUT
MAX25232ATCA,
MAX25232ATCB,
MAX25232ATCG,
MAX25232ATCH
PWM mode
Skip mode
90
PGOOD Debounce
Time
t
µs
DEB
MAX25232ATCD,
MAX25232ATCE,
MAX25232ATCF
PWM mode
Skip mode
80
110
PGOOD High-Leakage
Current
I
T
= +25°C
1
µA
V
LEAK,PGD
A
PGOOD Low Level
LOGIC LEVELS
EN Level, High
EN Level, Low
V
Sinking 1mA
0.4
OUT,PGD
V
2.4
1.7
V
V
IH,EN
V
0.6
1
IL,EN
IN,EN
EN Input Current
I
V
= V
= 14V, T = +25°C
µA
EN
SUP
A
MAX25232ATCA, MAX25232ATCB,
MAX25232ATCG, MAX25232ATCH
2.6
MHz
kHz
External Input Clock
Frequency
FSYNC
MAX25232ATCD, MAX25232ATCE,
MAX25232ATCF
325
1.4
500
SYNC Threshold, High
SYNC Threshold, Low
SYNC Internal Pulldown
SPS Threshold, High
SPS Threshold, Low
SPS Internal Pulldown
THERMAL PROTECTION
Thermal Shutdown
V
V
V
IH,SYNC
V
0.4
0.4
IL,SYNC
R
1000
1000
kΩ
V
PD,MODE
V
1.4
IH,SPS
V
V
IL,SPS
kΩ
T
(Note 3)
(Note 3)
175
15
°C
°C
SHDN
Thermal-Shutdown
Hysteresis
T
SHDN.HYS
Note 2: Limits are 100% tested at T = +25°C. Limits over the operating temperature range and relevant supply voltage are guaranteed
A
by design and characterization. Typical values are at T = +25°C.
A
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Maxim Integrated | 5
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
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 T = +125°C for 95,000 hours and T = +150°C for 5,000 hours.
J
J
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Maxim Integrated | 6
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Operating Characteristics
(V
= V
= +14V, T = +25°C, unless otherwise noted.)
EN A
SUP
QUIESCENT SUPPLY CURRENT
EFFICIENCY vs. LOAD
(fSW= 2.1MHz)
EFFICIENCY vs. LOAD
vs. INPUT VOLTAGE
(fSW= 400kHz)
3.3V
(SKIP MODE)
toc03
toc01
toc02
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
25
20
15
10
5
SKIP
5V
5V
NO LOAD
SKIP
3.3V
3.3V
3.3V
5V
5V
5V , 400kHz
OUT
3.3V , 400kHz
OUT
FPWM
5V , 2.1MHz
OUT
FPWM
VIN= 14V
VIN= 14V
L = 2.2 µH
3.3V , 2.1MHz
OUT
L = 10µH
0
0.001
0.01
0.1
1
0.001
0.01
0.1
1
6
16
26
36
LOAD CURRENT (A)
LOAD CURRENT (A)
VIN(V)
SHUTDOWN SUPPLY CURRENT
vs. INPUT VOLTAGE
LINE REGULATION
(5VOUT, 2.1MHz)
STANDBY CURRENT
vs. LOAD CURRENT
(5V , 2.1MHz)
OUT
toc05
toc06
toc04
10
500
450
400
350
300
250
200
150
100
50
2.0
1.5
VEN= 0V
1A LOAD
FPWM
5V, 400kHz
5V, 2.1MHz
1.0
0.5
1
0.0
SKIP
3.3V, 2.1MHz
-0.5
-1.0
-1.5
-2.0
3.3V, 400kHz
0.1
0
6
16
IN(V)
26
36
0.0
0.2
0.4
0.6
0.8
1.0
6
16
26
36
VIN (V)
ILOAD(mA)
V
LINE REGULATION
(5VOUT, 400kHz)
LOAD REGULATION
(5VOUT, 2.1MHz)
LOAD REGULATION
(5VOUT, 400kHz)
toc07
toc08
toc09
2.0
1.5
2.0
1.5
2.0
1.5
1A LOAD
FPWM
VIN= 14V
VIN= 14V
1.0
1.0
1.0
SKIP
0.5
0.5
0.5
FPWM
0.0
0.0
0.0
SKIP
FPWM
SKIP
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
-2.0
6
16
26
36
0.0
0.5
1.0
1.5
2.0
2.5
0.0
0.5
1.0
1.5
2.0
2.5
VIN (V)
IOUT(A)
IOUT(A)
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Maxim Integrated | 7
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Operating Characteristics (continued)
(V
= V
= +14V, T = +25°C, unless otherwise noted.)
EN A
SUP
SHUTDOWN WAVEFORM
(5VOUT, 2.1MHz, 2.5A LOAD)
STARTUP WAVEFORM
(5VOUT, 2.1MHz)
STEAD-YSTATE SWITCHING WAVEFORM
(5VOUT, 2.1MHz, NO LOAD
toc11
toc12
toc10
VEN
V
EN
5V/div
5V/div
7V/div
VLX
5V/div
2A/div
5V/div
5V/div
IINDUCTOR
V
PGOOD
200mA/div
VPGOOD
IINDUCTOR
5V/div
5V/div
V
OUT
VOUT
VOUT
1ms/div
200ns/div
100µs/div
SLOW IVN RAMP
(5VOUT, 2.1MHz)
UNDERVOLTAGE PULSE
(5VOUT, 2.1MHz)
SHOR-TCIRCUIT RESPONSE
(5VOUT, 2.1MHz)
toc13
toc15
toc14
10mA Load
VOUT
VPGOOD
VBIAS
5V/div
V
5V/div
5V/div
5V/div
IN
V
IN
5V/div
5V/div
5V/div
VOUT
VBIAS
VOUT
2V/div
5V/div
5V/div
VPGOOD
IINDUCTOR
VPGOOD
1A/div
5µs/div
10ms/div
5s/div
SPECTRA-ELNERGY DENSITY
vs. FREQUENCY
LOAD-TRANSIENT RESPONSE
LOAD-DUMP TEST
(5VOUT, 2.1MHz)
(5V , 2.1MHz)
(5V , 2.1MHz)
OUT
OUT
toc16
toc17
toc19
0
VSPS= 5V
-10
-20
-30
-40
-50
-60
-70
-80
-90
V
IN
10V/div
1A/div
ILOAD
VOUT
5V/div
5V/div
100mV/div
(AC-
COUPLED)
VOUT
VBIAS
1.85
1.95
2.05
2.15
2.25
2.35
20µs/div
100ms/div
FREQUENCY (MHz)
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Maxim Integrated | 8
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Operating Characteristics (continued)
(V
= V
= +14V, T = +25°C, unless otherwise noted.)
EN A
SUP
SHOR-TCIRCUIT RESPONSE
(3.3VOUT, 400kHz)
toc19
VOUT
5V/div
5V/div
VPGOOD
5V/div
2A/div
VBIAS
IINDUCTOR
10µs/div
Pin Configurations
MAX25232ATCA, MAX25232ATCB, MAX25232ATCD, MAX25232ATCE, MAX25232ATCH
MAX25232ATCA
MAX25232ATCB
MAX25232ATCD
MAX25232ATCE
MAX25232ATCH
TDFN-EP
(3mm x 3mm)
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Maxim Integrated | 9
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
MAX25232ATCF, MAX25232ATCG
MAX25232ATCF
MAX25232ATCG
TDFN-EP
(3mm x 3mm)
Pin Description
PIN
MAX25232A
TCA,
MAX25232A
TCB,
MAX25232A
TCD,
MAX25232A
TCE,
MAX25232A
TCF,
MAX25232A
TCG
NAME
FUNCTION
MAX25232A
TCH
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.
SPS
SPS
1
EN
EN
2
3
4
High-Voltage-Compatible Enable Input. If this pin is low, the part is off.
Bootstrap Pin for HS Driver. It is recommended to use 0.1μF from BST to LX.
Supply Input. Connect a 4.7μF ceramic capacitor from SUP to PGND.
BST
SUP
BST
SUP
Buck Switching Node. Connect inductor between LX and OUT. See the Inductor
Selection section. If the part is off, this node is high impedance.
LX
LX
5
Power Ground. Ground return path for all high-current/high-frequency noisy
signals.
PGND
AGND
NC
PGND
AGND
FB
6
7
8
Analog Ground. Ground return path for all ‘quiet’ signals.
Leave this pin unconnected for fixed output voltage options. For MAX25232ATCF
and MAX25232ATCG, use it as a FB pin to set the output voltage.
Buck Regulator Output-Voltage-Sense Input. Bypass OUT to PGND with ceramic
capacitors.
OUT
OUT
9
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Maxim Integrated | 10
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Pin Description (continued)
PIN
MAX25232A
TCA,
MAX25232A
TCB,
MAX25232A
TCD,
MAX25232A
TCE,
MAX25232A
TCF,
MAX25232A
TCG
NAME
FUNCTION
MAX25232A
TCH
BIAS
BIAS
10
11
5V Internal Bias Supply. Connect a 1μF (min) ceramic capacitor to AGND.
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.
SYNC
SYNC
PGOOD
-
PGOOD
—
12
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.
EP
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Maxim Integrated | 11
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
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 resistor-
divider. 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 V
has exceeded the internal undervoltage-lockout level, V
= 2.73V (typ).
UVLO
BIAS
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 forced-
PWM 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 high-
voltage LDO is turned off to save current. V
is supplied by the output after the soft start is completed.
BIAS
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 | 12
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
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 V
and an
OUT
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 | 13
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Applications Information
Setting the Output Voltage
MAX25232 comes with fixed V
options (set internally) of 5V and 3.3V. For setting the output voltage between 3V
OUT
- 10V externally using resistor-dividers, chose MAX25232ATCF and MAX25232ATCG. Connect a resistor-divider from
output (OUT) to FB to AGND (see Figure 1). Select R
resistor) with the following equation:
(FB to AGND resistor) ≤ 500kΩ. Calculate R
(OUT to FB
FB1
FB2
V
OUT
R
= R
− 1
FB1
FB2
V
[
]
[
]
FB
where V = 1V (see Electrical Characteristics).
FB
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.
V
OUT
R
FB1
MAX25232ATCF
MAX25232ATCG
FB
R
FB2
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 input-
capacitance requirement. The input ripple is mainly comprised of ΔV (caused by the capacitor discharge) and ΔV
Q
ESR
(caused by the ESR of the input capacitor). The total voltage ripple is the sum of ΔV and ΔV
. Assume that input-
Q
ESR
voltage 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 | 14
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
∆ V
ESR
ESR =
I
+ ( ∆ I
2)
/
OUT
P−P
I
× D(1 − D)
OUT
∆ V × × f
C
=
IN
Q
SW
where:
(V − V
) × V
IN
OUT
× f
OUT
× L
∆ I
=
P − P
V
IN SW
and:
V
OUT
D =
V
IN
where I
is the output current, D is the duty cycle, and f
is the switching frequency. Use additional input capacitance
SW
OUT
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 f
For f
= 2.1MHz
= 400kHz
2.2
10
SW
SW
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 f
For f
= 2.1MHz
= 400kHz
30
44
SW
SW
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 ΔV (caused by the capacitor discharge) and ΔVESR
Q
(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 ΔV
. Use Equation 2 to calculate the
ESR
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:
∆ V
ESR
ESR =
∆ I
P−P
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Maxim Integrated | 15
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
∆ I
P−P
C
=
OUT
8 × ∆ V × f
Q
SW
where:
(V − V
) × V
IN
OUT
× f
OUT
× L
∆ I
=
P − P
V
IN SW
and:
V
= ∆ V
+ ∆ V
OUT_RIPPLE
ESR Q
ΔI
is the peak-to-peak inductor current as calculated above, and f
is the converter’s switching frequency. The
SW
P-P
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:
∆ V
ESR
ESR
=
OUT
I
STEP
L
2
C
≥ I
×
OUT
STEP
2 × (V
− V
) × DMAX × ∆ V
SUP
OUT
Q
t
DELAY
+ I
×
STEP
∆ V
Q
where I
is the load step and t
is the delay for the PWM mode, the worst-case delay would be (1-D) t
when
SW
STEP
DELAY
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 (C ) close to the device to reduce the input AC-current loop. AC current flows on the loop
IN
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 (C
) close to the device to reduce the bias current loop. This helps to reduce noise on the
BIAS
bias for smoother operation.
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Maxim Integrated | 16
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
GROUND
SUP
MAX25232
VCC
C
BIAS
LX
C
IN
AC current
loop
INDUCTOR
GROUND
VIAS
GROUND
GROUND
OUT
Figure 2. Recommended PCB Layout for MAX25232
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Maxim Integrated | 17
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Application Circuits
Circuit 1
MAX25232
SUP
BST
L
C
BST
2.2µH
C
IN
0.1µF
4.7µF
LX
NH
NL
OUT
C
30µF
OUT
SYNC
EN
PGOOD
BIAS
C
1µF
BIAS
SPS
AGND
PGND
Figure 3. 2.1MHz, 5V/3.3V Fixed Output Voltage Configuration in 12-Pin TDFN Package
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Maxim Integrated | 18
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Application Circuits (continued)
Circuit 2
MAX25232
SUP
BST
L
C
BST
10µH
C
IN
0.1µF
4.7µF
LX
NH
NL
OUT
C
44µF
OUT
SYNC
EN
PGOOD
BIAS
C
1µF
BIAS
SPS
AGND
PGND
Figure 4. 400kHz, 5V/3.3V Fixed Output Voltage Configuration in 12-Pin TDFN Package
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Maxim Integrated | 19
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Typical Application Circuits (continued)
Circuit 3
MAX25232
SUP
BST
L
C
BST
10µH
C
IN
0.1µF
4.7µF
LX
NH
NL
OUT
SYNC
C
OUT
44µF
R
FB1
EN
FB
PGOOD
BIAS
R
FB2
C
1µF
BIAS
SPS
AGND
PGND
Figure 5. 400kHz, External Resistor-Divider Configuration in 12-Pin TDFN Package
Ordering Information
PIN-
PACKAGE
I
OUT
(A)
PART
TEMP RANGE
DESCRIPTION
2.1MHz, Fixed 5V output
MAX25232ATCA/V+
MAX25232ATCB/V+
MAX25232ATCD/V+*
MAX25232ATCE/V+*
-40°C to +125°C 12 TDFN
-40°C to +125°C 12 TDFN
-40°C to +125°C 12 TDFN
-40°C to +125°C 12 TDFN
2.5
2.5
3
2.1MHz, Fixed 3.3V output
400kHz, Fixed 5V output
400kHz, Fixed 3.3V output
3
400kHz, Adjustable Output Voltage Between 3V
and 10V
MAX25232ATCF/V+
-40°C to +125°C 12 TDFN
3
2.1MHz, Adjustable Output Voltage Between 3V
and 10V
MAX25232ATCG/V+
MAX25232ATCH/V+*
-40°C to +125°C 12 TDFN
-40°C to +125°C 12 TDFN
2.5
2.5
2.1MHz, Fixed 4V output
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 | 20
MAX25232
36V, 3A Mini Buck Converters with 3.5μA I
Q
Revision History
REVISION REVISION
PAGES
DESCRIPTION
CHANGED
NUMBER
DATE
0
7/20
Initial release
—
Updated Benefits and Features, Electrical Characteristics, Pin Configuration, Pin
Description, Applications Information, and Ordering Information
1, 4, 5, 9, 10, 14,
20
1
10/20
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.
© 2020 Maxim Integrated Products, Inc.
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