MAX20457ATIG [MAXIM]
High-Efficiency, 36V, Dual Synchronous Buck Converters (3.5A/2A) for Automotive Applications;
| 型号： | MAX20457ATIG |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | High-Efficiency, 36V, Dual Synchronous Buck Converters (3.5A/2A) for Automotive Applications |
| 文件： | 总17页 (文件大小：1479K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
General Description
Benefits and Features
● Meets Stringent OEM Module Power Consumption
The MAX20457 offers two automotive grade synchronous
buck converters with fixed frequency of either 2.1MHz or
400kHz. The two high-voltage synchronous step-down
converters operate 180° out-of-phase. The IC operates
with an input voltage supply from 3.5V to 36V and can
operate in dropout conditions by running at 95% duty
cycle. It is intended for applications with mid- to high-
power requirements that operate at a wide input voltage
range such as during automotive cold-crank or engine
stop-start conditions.
and Performance Specifications
• 10μA Supply Current with 5V Buck On
• 8μA Supply Current with 3.3V Buck On
• 10μA Supply Current with Both Bucks On
● Enables Crank-Ready Designs
• Wide Input Supply Range from 3.5V to 36V
● EMI Reduction Features Reduce Interference with
Sensitive Radio Bands without Sacrificing Wide Input
Voltage Range
High switching frequency up to 2.1MHz allows small
external components, reduced output ripple, and guaran-
tees no AM band interference. The switching frequency is
fixed at 400kHz or 2.1MHz. FSYNC input programmability
enables three modes for optimized performance: forced
fixed-frequency operation, skip mode with ultra-low qui-
escent current, and phase-locked synchronization to an
external clock. The spread spectrum option minimizes
EMI interference.
• 20ns (typ) Minimum On-Time Guarantees Skip-
Free Operation for 3.3V Output at 2.1MHz
• Spread-Spectrum Option
• Phase-Locked Loop (PLL) Frequency
Synchronization
● Integration and Thermally Enhanced Packages Save
Board Space and Cost
• Two 2.1MHz Current-Mode Converters with Forced
Fixed Frequency and Skip Modes
The IC features the power-OK indicators and undervolt-
age lockout for the buck converters. Protection features
include cycle-by-cycle current limit and thermal shutdown.
The MAX20457 is specified for operation over the -40°C
to +125°C automotive temperature range.
• Thermally Enhanced 5mm x 5mm, 28-Pin TQFN-
EP Package
● Protection Features Improve System Reliability
• Supply Undervoltage Lockout
• Overtemperature and Short-Circuit Protection
Applications
● Automotive Start-Stop System
Ordering Information appears at end of data sheet.
● Instrument Cluster
● Distributed DC Power Systems
● Navigation and Radio Head Units
19-100476; Rev 3; 11/19
MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Simplified Block Diagram
BUCK1 CONTROL LOGIC
PGOOD
PGOOD1
MAX20457
COMP
THRESHOLD
FB1
FEEDBACK
SELECT
LOGIC
SUPSW1
EAMP1
BST1
INTERNAL
SOFT
EN1
START
OUT1
EN1
BUCK1
GATE DRIVE
LOGIC
PWM1
LX1
PWM1
CURRENT SENSE
AND SLOPE COMP
BIAS
LX1
CLK1
CLK1
BIAS
PGND1
SPREAD SPECTRUM
ON/OFF OPTION
OSCILLATOR
PLL/SYNC
DETECTION
INTERNAL
LINEAR
BIAS
BIAS
REGULATOR
FSYNC
SELECT
LOGIC
FSYNC
CLK 180º
OUT OF PHASE
PGND
AGND
EXTVCC
SWITCHOVER
BIAS
SUPSW2
BST2
CLK2
FB2
EN2
BUCK2
OUT2
EN2
GATE DRIVE
LOGIC
BUCK2 CONTROL LOGIC
SAME AS BUCK1
LX2
PWM2
CLK2
BIAS
PGOOD2
PGND2
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Absolute Maximum Ratings
SUPSW1, SUPSW2, EN1, EN2 to AGND ..............-0.3V to 40V
OUT1, OUT2 to AGND............................................-0.4V to 15V
BIAS, FSYNC, PGOOD1, PGOOD2,
Continuous Power Dissipation (T = +70°C)
A
TQFN (derate 28.6mW/°C above +70°C)..................2286mW
Operating Temperature Range............................-40°C to 125°C
Junction Temperature .....................................................+150°C
Soldering Temperature (reflow).......................................+260°C
Storage Temperature Range............................ -65°C to +150°C
Lead Temperature(soldering,10s) .....................................300°C
FB1, FB2 to AGND................................................-0.3V to 6V
EXTVCC to AGND...................................-0.3V to (BIAS + 0.3V)
LX_ to PGND_ ................................-0.3V to (SUPSW_ + 0.3V)
BST_ to LX_ (Note 1)................................................-0.3V to 6V
PGND_ to AGND....................................................-0.3V to 0.3V
Note 1: Self-protected against transient voltages exceeding these limits for ≤ 50ns under normal operation and loads up to the
maximum rated output current.
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
Package Type
28 TQFN
T2855Y+5C
21-100130
90-0027
Package Code
Outline Number
Land Pattern Number
THERMAL RESISTANCE, FOUR-LAYER BOARD (Note 2)
Junction to Ambient (θ
)
27°C/W
3°C/W
JA
Junction to Case (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.
Note 2: Package thermal resistances were obtained using the Evaluation Kit. For detailed information on package thermal consider-
ations, refer to www.maximintegrated.com/thermal-tutorial.
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Electrical Characteristics
V
= 14V, V
= 14V, T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C) (Notes 3 and 4)
SUPSW_
EN_ J A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SYNCHRONOUS STEP-DOWN CONVERTERS
Supply Voltage Range
Supply Current
V
Normal operation
3.5
36
5
V
SUP
V
= V = 0V
EN2
1
EN1
V
V
= V
, V
=5V, V
= 0V,
EN1
SUP OUT1
EN2
10
18
= 5V, No Switching
EXTVCC
V
V
= V
= 0V, V
, V
= 3.3V,
= 3.3V,
EN2
SUP OUT2
I
µA
8
12
IN
EN1
EXTVCC
no switching
V
V
= V
= V
, V
= 5V,
= 3.3V,
EN1
EN2
SUP OUT1
= 3.3V, V
10
OUT2
EXTVCC
no switching
V
V
V
V
= V
= V
= V
= V
, V
= 5V, PWM mode
= 5V, skip mode
4.9
4.85
3.234
3.2
5
5.1
5.15
3.366
3.4
FB1
FB1
FB2
FB2
BIAS OUT1
BUCK1 Fixed Output Voltage
BUCK2 Fixed Output Voltage
V
V
V
OUT1
, V
5
BIAS OUT1
, V
= 3.3V, PWM mode
= 3.3V, skip mode
3.3
3.3
BIAS OUT2
V
V
OUT2
, V
BIAS OUT2
Output Voltage Adjustable
Range
BUCK1, BUCK2 (Note 5)
1
14
Regulated Feedback Voltage
Feedback Leakage Current
V
I
, V
0.985
1
1.015
1
V
FB1 FB2
, I
T
= +25°C
0.01
μA
FB1 FB2
A
Feedback Line Regulation
Error
V
= 3.5V to 36V, V
= 1V
0.01
3
%/V
SUP
FB_
Dead time
BUCK1, BUCK2 (Note 5)
BUCK1, BUCK2
BUCK1, BUCK2 (Note 5)
2.1MHz
ns
%
Maximum Duty Cycle
Minimum On-Time
95
t
20
2.1
400
6
ns
ON_MIN
1.9
350
4.5
2.5
2.32
470
7.5
MHz
kHz
Switching Frequency
Accuracy
400kHz
BUCK1
Current-Limit
A
BUCK2
3.5
4.5
BUCK1 and BUCK2, fixed soft-start time
regardless of frequency.
Soft-Start Ramp Time
3
5.5
180
0.001
50
7
ms
deg
μA
Phase Shift Between BUCK1
and BUCK2
PWM operation (Note 5)
V
= 6V, V
= V
or V
,
SUP
LX_
PGND_
SUP
LX1, LX2 Leakage Current
5
T = +25°C
A
R
ON_H_
BUCK1
I
= 1A, V
= 5V
= 5V
LX1
LX2
BIAS
High-Side Switch On
Resistance
mΩ
R
ON_H_
I
= 1A , V
100
BIAS
BUCK2
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Electrical Characteristics (continued)
V
= 14V, V
= 14V, T = -40°C to +150°C, unless otherwise noted. Typical values are at T = +25°C) (Notes 3 and 4)
SUPSW_
EN_ J A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
45
MAX
UNITS
R
R
I
= 1A, V
= 5V
BIAS
Low-Side Switch On
Resistance
ON_L_BUCK1 LX1
mΩ
I
= 1A, V
= 5V
BIAS
90
ON_L_BUCK2 LX2
V
% of V
, rising
93
95
97
PGOOD1, PGOOD2
Threshold
PGOOD_H
OUT_
%
V
% of V
, falling
91.5
93.5
95.5
PGOOD_F
OUT_
PGOOD1, PGOOD2 Leakage
Current
V
= V
= 5V, T = +25°C
0.01
1
μA
V
PGOOD1
PGOOD2
A
PGOOD1, PGOOD2 Output
Low Voltage
I
= 1mA
0.2
SINK
PGOOD1, PGOOD2
Debounce Time
Fault detection, rising and falling
20
0
μs
ms
PGOOD1, PGOOD2 Assertion
Time
PGOOD1, PGOOD2 low to high (Note 5)
FSYNC INPUT
Minimum sync pulse of 100ns,
1.8
2.6
MHz
kHz
f
= 2.1MHz
OSC
FSYNC frequency Range
Minimum sync pulse of 1.5μs,
= 400kHz
250
1.4
550
f
OSC
High Threshold
Low Threshold
FSYNC Switching Thresholds
V
0.4
3.3
INTERNAL LDO BIAS AND EXTVCC
Internal BIAS Voltage
V
V
V
> 6V
5
V
V
SUPSW1
rising
3.1
2.6
BIAS
BIAS
BIAS UVLO Threshold
falling
2.4
EXTVCC Operating Range
3.25
5.5
V
V
EXTVCC Threshold
V
EXTVCC rising, hysteresis = 110mV
3
3.25
TH_EXTVCC
THERMAL OVERLOAD
Thermal Shutdown
Temperature
(Note 5)
(Note 5)
170
20
°C
°C
Thermal Shutdown Hysteresis
EN Logic Input
High Threshold
EN_
EN_
1.8
V
V
Low Threshold
0.8
1
EN Input Bias Current
SPREAD SPECTRUM
EN_ Logic Inputs Only, T = +25°C
A
0.01
μA
f
OSC
±6%
Spread Spectrum
Spread spectrum enabled
Note 3: Limits are 100% tested at +25°C. Limits over operating temperature range and relevant supply voltage are guaranteed by
design and characterization. Typical values are at +25°C.
Note 4: 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
Note 5: Guaranteed by design, not production tested.
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Typical Operating Characteristics
(T = +25ºC, unless otherwise noted.)
A
QUIESCENT CURRENT
vs. SUPPLY VOLTAGE
STARTUP INTO NO-LOAD
STARTUP INTO LOAD
toc01
toc03
30
25
20
15
10
5
toc02
5V/div
ONLY BUCK1 ON, EXTVCC = VOUT1
ONLY BUCK2 ON, EXTVCC = VOUT2
BOTH BUCK1 AND BUCK2 ON,
EXTVCC = VOUT2
VEN
5V/div
VEN
5V/div
5V/div
5V/div
5V/div
VOUT1
VOUT1
EN1 = EN2
FSYNC = 1
VIN = 14V
EXTVCC = VOUT1
VPGOOD1
VPGOOD1
EN1 = EN 2
FSYNC = 1
EXTVCC = VOUT1
VIN = 14V
5V/div
5V/div
VOUT2
IOUT1 = 3A, IOUT2 = 1.5A
5V/div
5V/div
VOUT2
VPGOOD2
VPGOOD2
1ms/div
0
1ms/div
0
5
10
15
20
25
30
35
INPUT VOLTAGE (V)
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
BUCK2 EFFICIENCY
vs. LOAD CURRENT
BUCK1 EFFICIENCY
vs. LOAD CURRENT
toc05
toc04
toc06
7
6
5
4
3
2
1
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
SKIP
FPWM
SKIP
FPWM
V
V
V
= V
= 3.3V
= 14V
= 2.1MHz
= 5V
OUT1
V
V
f
= V
= 14V
= 2.1MHz
= 5V
OUT1
EXTVCC
EXTVCC
OUT2
IN
IN
SW
EN1 = HIGH
EN2 = LOW
f
SW
EN1 = EN2 = HIGH
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
LOAD CURRENT (A)
0
6
12
18
24
30
36
0.0
0.5
1.0
1.5
2.0
INPUT VOLTAGE (V)
LOAD CURRENT (A)
SWITCHING FREQUENCY
vs. LOAD CURRENT
SWITCHING FREQUENCY
vs. AMBIENT TEMPERATURE
toc07
toc08
2.15
2.14
2.13
2.12
2.11
2.10
2.09
2.08
2.07
2.06
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
1.95
1.90
1.85
MEASURED ON BUCK1
IOUT1 = 3A
MEASURED ON BUCK1
IOUT1 = 3A
2.05
0.0
1.80
0.5
1.0
1.5
2.0
2.5
3.0
3.5
-40 -25 -10
5
20 35 50 65 80 95 110 125
LOAD CURRENT (A)
AMBIENT TEMPERATURE (°C)
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Typical Operating Characteristics (continued)
(T = +25ºC, unless otherwise noted.)
A
FSYNC SYNCHRONIZATION
OUT OF PHASE OPERATION
SWITCHING WAVEFORM
toc11
toc09
toc10
5V/div
5V/div
VFSYNC
VFSYNC
ILX
1A/div
1.8MHz, 50% DUTY CYCLE SIGNAL ON FSYNC
VIN = 6V, IOUT1 = 3A, IOUT2 = 1.5A
2.6MHz, 50% DUTY CYCLE SIGNAL ON FSYNC
VIN = 6V, IOUT1 = 3A, IOUT2 = 1.5A
VLX
10V/div
VLX1
VLX1
10V/div
10V/div
10V/div
10V/div
VLX2
VLX2
20mV/div
(1.8V OFFSET)
VOUT1
1µs/div
1µs/div
200ns/div
CONDITIONS: VIN = 18V, VOUT2 = 1.8V, fSW = 2.1MHz, IOUT2 = 1A
LOAD TRANSIENT RESPONSE
(BUCK1)
LOAD TRANSIENT RESPONSE
(BUCK2)
toc13
toc12
IOUT2
IOUT1
1A/div
2A/div
200mV/div
200mV/div
(3.3V OFFSET)
(5V OFFSET)
VOUT2
VOUT1
100µs/div
100µs/div
CONDITIONS: VOUT1 = 5V, fSW = 2.1MHz, FSYNC = HIGH, EN1 ONLY
CONDITIONS: VOUT1 = 3.3V, fSW = 2.1MHz, FSYNC = HIGH, EN1 ONLY
OUTPUT LINE REGULATION
OUTPUT LOAD REGULATION
(BUCK2)
OUTPUT LOAD REGULATION
(BUCK1)
(BUCK1)
toc16
toc14
toc15
5.05
5.04
5.03
5.02
5.01
5.00
4.99
4.98
4.97
4.96
4.95
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
3.50
3.45
3.40
3.35
3.30
3.25
3.20
3.15
3.10
SKIP
SKIP
LOAD = 1A
FWPM
LOAD = 3A
FPWM
VEXTVCC = VOUT1 = 5V
V
= V
= 2.1MHz
= 3.3V
1.5
EXTVCC
OUT2
fSW = 2.1MHz
EN1 = HIGH
EN2 = LOW
VEXTVCC = VOUT1 = 5V
fSW = 2.1MHz
f
SW
EN2 = HIGH
EN1 = LOW
6
12
18
24
30
36
0.0
0.5
1.0
2.0
0
0.5
1
1.5
2
2.5
3
3.5
INPUT VOLTAGE (V)
OUTPUT LOAD (A)
OUTPUT LOAD (A)
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Typical Operating Characteristics (continued)
(T = +25ºC, unless otherwise noted.)
A
OUTPUT LINE REGULATION
(BUCK2)
CRANK
DIPS AND DROPS
toc19
toc17
toc18
3.33
14V
14V
16V
16V
7.5V
6.5V
10V/div
5.5V
10V/div
5V
3.32
3.31
3.5V
VBATT
VBATT
(DIGITAL)
PGOOD1
VOUT1
VEXTVCC = GND, VOUT1 = 5V,
VOUT2 = 3.3V,
fSW = 2.1MHz, IOUT1 = IOUT2 = 1A
1V/div
(5V OFFSET)
200mV/div
(5V OFFSET)
VOUT1
LOAD = 0.5A
3.30
(DIGITAL)
PGOOD1
LOAD = 2A
3.29
(DIGITAL)
PGOOD2
VOUT2
200mV/div
(3.3V OFFSET)
VOUT1 = 5V, VOUT2 = 3.3V,
VEXTVCC = GND, fSW = 2.1MHz, NO LOAD
VEXTVCC = VOUT1 = 5V
VOUT2 = 3.3V
VOUT2
3.28
200mV/div
(3.3V OFFSET)
(DIGITAL)
PGOOD2
fSW = 2.1MHz
3.27
6
12
18
24
30
36
100.0ms/div
20.0ms/div
INPUT VOLTAGE (V)
SLOW VIN RAMP
LOAD DUMP
toc20
toc21
20V/div
20V/div
2V/div
VBATT
VBATT
VEXTVCC = VOUT1 = 5V
VOUT2 = 3.3V
fSW = 2.1MHz
VOUT2
IOUT1 = IOUT2 = 1A
200mV/div
(5V OFFSET)
VOUT1
PGOOD1
(DIGITAL)
VOUT1 = 5V, VOUT2 = 3.3V,
V
EXTVCC = GND, fSW = 2.1MHz,
200mV/div
(3.3V OFFSET)
2V/div
IOUT1 = IOUT2 = 1A
VOUT1
VOUT2
PGOOD2
(DIGITAL)
10.0s/div
20.0ms/div
SHORT CIRCUIT AFTER REGULATION
(BUCK2)
SHORT-CIRCUIT AFTER REGULATION
(BUCK1)
toc23
toc22
5V/div
5V/div
5A/div
5V/div
VOUT2
VOUT1
VPGOOD2
VPGOOD1
5V/div
5A/div
ILX2
ILX1
VLX2
10V/div
VLX1
10V/div
400µs//div
10ms/div
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Pin Configuration
TOP VIEW
21 20 19 18 17 16 15
22
23
24
25
26
27
28
14
N.C.
PGND
PGOOD2
13 LX2
12
PGND2
11 PGND1
PGND
MAX20457
AGND
10
9
BIAS
LX1
LX1
EXTVCC
FSYNC
+
8
PGOOD1
1
2
3
4
5
6
7
TQFN
5mm x 5mm
Pin Description
PIN
1
NAME
PGND
EN2
FUNCTION
Power Ground
2
High-Voltage Tolerant, Active High Digital Enable Input for BUCK2. Drive EN2 high to enable BUCK2.
High-Voltage Tolerant, Active High Digital Enable Input for BUCK1. Drive EN1 high to enable BUCK1.
3
EN1
Output Sense Input for BUCK1. When using the internal preset 5V feedback divider, FB1 is connected to
BIAS, and BUCK1 uses OUT1 to sense the output voltage.
4
OUT1
Feedback Input for BUCK1. Connect FB1 to BIAS for fixed output or to a resistor divider between OUT1
and AGND to adjust the output voltage between 1V and 14V. FB1 is regulated to 1V (typ) in
adjustable version.
5
FB1
BUCK1 Internal High-Side Switch Supply Input and BIAS LDO Input. Bypass SUPSW1 to PGND1 with a
4.7μF ceramic capacitor.
6
7
SUPSW1
Boost Flying Capacitor Connection for High-Side Gate Voltage of BUCK1. Connect a ceramic capacitor
between BST1 and LX1.
BST1
Open Drain Power-Good Output for BUCK1. PGOOD1 is low if OUT1 falls below 93.5% (typ) of output
regulation voltage. PGOOD1 becomes high impedance when OUT1 rises above 95% (typ) of its
regulation voltage. PGOOD1 asserts low during soft-start and in shutdown. To obtain a logic signal, pull
up PGOOD1 with an external resistor connected to a positive voltage lower than 5.5V.
8
PGOOD1
9, 10
11
LX1
PGND1
PGND2
LX2
BUCK1 Inductor Connection. Connect an inductor from LX1 to the BUCK1 output.
Power Ground for BUCK1
12
Power Ground for BUCK2
13
BUCK2 Inductor Connection. Connect an inductor from LX2 to the BUCK2 output.
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Pin Description (continued)
PIN
NAME
FUNCTION
Open Drain Power-Good Output for BUCK2. PGOOD2 is low if OUT2 falls below 93.5% (typ) of output
regulation voltage. PGOOD2 becomes high impedance when OUT2 rises above 95% (typ) of its
regulation voltage. PGOOD2 asserts low during soft-start and in shutdown. To obtain a logic signal, pull
up PGOOD2 with an external resistor connected to a positive voltage lower than 5.5V.
14
PGOOD2
Boost Flying Capacitor Connection for High-Side Gate Voltage of BUCK2. Connect a ceramic capacitor
between BST2 and LX2.
15
16
BST2
BUCK2 Internal High-Side Switch Supply Input. Bypass SUPSW2 to PGND2 with a 4.7μF ceramic
capacitor.
SUPSW2
Feedback Input for BUCK2. Connect FB2 to BIAS for fixed output or to a resistive divider between OUT2
and AGND to adjust the output voltage between 1V and 14V. FB2 is regulated to 1V (typ) in the
adjustable version.
17
18
FB2
Output Sense Input for BUCK2. When using the internal preset feedback divider, FB2 is connected to
BIAS and BUCK2 uses OUT2 to sense the output voltage.
OUT2
PGND
PGND3
19, 20,
23, 24
Power Ground
Power Ground for Boost Controller. All the high current paths for the boost controller terminates to
PGND3.
20
21, 22
25
N.C.
Not Connected
AGND
Quiet Analog Ground for the IC
5V Internal Linear Regulator Output. Bypass BIAS to ground with a low ESR minimum 2.2µF ceramic
capacitor. BIAS provides the power to the internal gate drive circuitry.
26
27
BIAS
Switchover Comparator Input. Connect a voltage between 3.25V and 5.5V to EXTVCC to power the IC
and bypass the internal bias LDO. Connect EXTVCC to ground if EXTVCC is not used.
EXTVCC
External Clock Synchronization Input. Synchronization operating frequency ratio is 1. The duty-cycle of
the signal on SYNC determines the phase shift between BUCK1 and BUCK2. Use 50% duty cycle for the
external clock to get a 180° phase shift between BUCK1 and BUCK2.
28
—
FSYNC
EP
Exposed Pad. Connect EP to ground. Connecting EP to ground does not remove the requirement for
proper ground connections to PGND and AGND. EP is attached with epoxy to the substrate of the die,
making it an excellent path to remove heat from the IC.
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
its LX1 falling edge to the FSYNC rising edge, and the
BUCK2 converter synchronizes its LX2 falling edge to
the FSYNC falling edge. The FSYNC signal should have
a minimum 100ns high pulse width for 2.1MHz and mini-
mum 1.5μs high pulse width for 400kHz.
Detailed Description
The MAX20457 IC is an automotive-grade switching power
supply that integrates two synchronous buck converters.
1) The BUCK1 converter provides a fixed 5V/3.3V out-
put voltage, or an adjustable 1V to 14V output voltage
option, and up to 3.5A continuous current capability.
Spread-Spectrum Option
The ICs feature enhanced EMI performance with spread
spectrum option. The spread spectrum is available as a
factory option. When the spread spectrum is enabled, the
operating frequency is varied ±6% centered at switching
frequency. The modulation signal is a triangular wave
with a period of 110μs at 2.1MHz. Therefore, switching
frequency ramps down 6% and back to 2.1MHz in 110μs
and also ramps up 6% and back to 2.1MHz in 110μs after
which the cycle repeats.
2) The BUCK2 converter provides a fixed 5V/3.3V out-
put voltage, or an adjustable 1V to 14V output voltage
option, and up to 2A continuous current capability.
Each power supply has its individual enable pin. Connect
EN1 or EN2 directly to battery voltage, or to power sup-
ply sequencing logic to control each power supply on/off.
In standby mode, the total supply current is reduced to
10μA (typ). When both converters are disabled, the total
current drawn is further reduced to 1μA.
For operations at 400kHz, the modulation signal scales
proportionally (the 110μs modulation period for 2.1MHz
increases to 110μs x 2.1MHz/0.4MHz = 577.5μs).
Internal 5V BIAS LDO
An internal 5V BIAS LDO supplies the IC internal circuitry.
SUPSW1 supplies the internal BIAS LDO. Bypass BIAS
with a minimum 2.2μF ceramic capacitor. To minimize the
internal power dissipation, bypass BIAS to an external 5V
rail using the EXTVCC pin.
The internal spread spectrum is disabled if the devices
are synchronized to an external clock. However, the
devices do not filter the input clock on the FSYNC pin and
pass any modulation (including spread spectrum) present
on the driving external clock.
EXTVCC Switchover
Overcurrent Protection
The internal linear regulator can be bypassed by connect-
ing an external 3.25V to 5.5V supply, or one of the buck
converter outputs to EXTVCC. With valid supply applied
to EXTVCC, BIAS is internally switched to EXTVCC and
the internal linear regulator turns off. This configuration
has two main advantages:
The MAX20457 has a cycle-by-cycle current limit and
includes hiccup mode to prevent any damage from over-
current or short-circuit on three power channels. When
the inductor current continuously hits the current limit at
overcurrent on any channels, the output voltage starts
decreasing. If the IC detects the output voltage drops
below 0.7V, it turns off that channel. After waiting for about
10ms (2x soft-start time) of hiccup time, the IC restarts
that channel in case the overcurrent or short-circuit condi-
tion is removed.
1) Reduces IC internal power dissipation
2) Improves light-load efficiency as the internal supply
current is scaled down proportionally to the duty cycle
if connecting any buck output to EXTVCC
If V
drops below 3V (typ), the internal regulator is
EXTVCC
Thermal Overload Protection
enabled and BIAS is switched back to 5V.
Thermal overload protection limits total power dissipation
in the ICs. When the junction temperature exceeds
+170°C, an internal thermal sensor shuts down the ICs,
allowing them to cool. The thermal sensor turns on the
ICs again after the junction temperature cools by 20°C.
Switching Frequency/External
Synchronization
The MAX20457 provides an internal oscillator with 400kHz
and 2.1MHz options. 2.1MHz frequency operation opti-
mizes the application for the smallest component size, at
the cost of lower efficiency. 400kHz frequency operation
offers best overall efficiency at the expense of component
size and board space.
Buck Converters
The ICs provide two synchronous buck converters. The
buck converters use PWM, valley current mode control
scheme, making it ideal for applications with high input
voltages and low output voltages. BUCK1 and BUCK2
operate 180 degrees out of phase with each other to
minimize input current ripple from the minimum to the
maximum input voltages.
Apply an external clock to FSYNC to enable frequency
synchronization. The MAX20457 uses a phase-locked
loop (PLL) to synchronize the internal oscillator to the
external clock signal. The BUCK1 converter synchronizes
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
of regulation, frequency foldback is used to automatically
reduce the switching frequency from 2.1MHz to 350kHz
and maintain a high duty cycle of > 95% with 100ns (typ)
off time. The frequency foldback occurs when the input
voltage drops below a certain threshold calculated by
Undervoltage Lockout (UVLO)
The internal 5V BIAS LDO undervoltage-lockout (UVLO)
circuitry inhibits switching if the BIAS voltage drops below
its 2.6V (typ) UVLO falling threshold. Once the BIAS volt-
age rises above its UVLO rising threshold, 3.1V (typ), and
EN1 and EN2 enable the buck converters, BUCK1 and
BUCK2 start switching and their output voltages begin
soft-start.
formula of V
= 1.4 x V
(falling).
SUPSW_
OUT_
Maximum Duty-Cycle Operation
When the buck input drops close to its output regula-
tion voltage, it enters maximum duty-cycle operation
with minimum 95% duty cycle, while switching at regular
switching frequency in the case of no frequency foldback,
or at 350kHz after frequency foldback. The input voltage
at which the buck enters dropout can be approximated
as follows:
Soft-Start
Drive EN1 and EN2 high to enable BUCK1 and BUCK2.
The soft-start circuitry gradually ramps up the reference
voltage during soft-start time (5ms typ) to reduce the input
surge currents during startup. BIAS voltage must exceed its
UVLO threshold (3.1V typ) before soft-start can be enabled.
V
= [V
+ (I
x RON_H_BUCK_)]/0.95
IN_
OUT_
OUT_
FSYNC Mode Selection
where RON_H_BUCK_ is listed in the EC table specifica-
tion.
Drive FSYNC low to enable skip mode. In skip mode, the
high-side FET turns for fixed adaptable on-time (depend-
ing on V
, V and f ). The high-side FET then
OUT SUP SW
turns off and the low-side FET turns on until the inductor
current falls to the zero cross threshold. Once the low-
side FET turns off by hitting the zero-crossing threshold,
LX becomes high impedance and the output voltage
keeps decreasing. When output voltage or FB voltage
is detected below the set point, the new cycle starts by
turning on the high-side FET again. In this way, the regu-
lator switches only as needed to service load to improve
system efficiency.
High-Side Gate Driver Supply (BST1/BST2)
The buck converter high-side MOSFET is turned on
by closing an internal switch between BST1/BST2 and
the gate of the high-side MOSFET and transferring the
bootstrap capacitor’s charge at BST1/BST2 to the gate
of the high-side MOSFET. This charge refreshes when
the high-side MOSFET turns off and the LX1/LX2 voltage
drops down to ground, taking the negative terminal of the
capacitor to the same potential. At this time, the bootstrap
diode recharges the positive terminal of the bootstrap
capacitor to BIAS voltage.
Drive FSYNC high to enable forced PWM (FPWM)
mode. FPWM mode prevents the regulator from entering
skip mode, by disabling the zero-cross detection of the
inductor current. The benefit of FPWM mode is to keep
the switching frequency constant under all load conditions;
however, FPWM operation diverts a considerable amount
of the output current to PGND, reducing the efficiency
under light-load conditions. FPWM mode is useful for
improving load-transient response and eliminating
unknown frequency harmonics that can interfere with AM
radio bands.
The selected n-channel high-side MOSFET determines the
appropriate boost capacitance values (C
in the Typical
BST_
Operating Circuit) according to the following equation:
C
= Q /ΔV
BST_
G
BST_
where Q is the total gate charge of the high-side
G
MOSFET and ΔV
is the voltage variation allowed
BST_
on the high-side MOSFET driver after turn-on. Choose
∆V such that the available gate-drive voltage is not
BST_
significantly degraded (e.g., ∆V
= 100mV to 300mV)
BST_
Frequency Foldback
when determining C
. The boost capacitor should be
BST_
Frequency Foldback is implemented in buck converters
when operating only at 2.1MHz and when the internal
fixed output voltage option is selected. This is useful in
case the boost controller is not used to protect its input
a low-ESR ceramic capacitor. A minimum value of 100nF
works in most cases.
Power Good Indicator (PGOOD1/PGOOD2)
voltage during V
transient drops. When the input
SUP
Each buck converter include a power good indicator to
indicate the buck output voltage status. The PGOOD_
indicator can be used to enable circuits that are supplied
by the corresponding voltage rail, or to turn-on subsequent
supplies.
voltage of buck converter drops close to the output volt-
age, the converter runs at the maximum duty cycle and
the high-side switch off period approaches minimum off
time 100ns (typ). To prevent output voltage drifting out
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Each PGOOD_ goes from low to high impedance when the
corresponding regulator output voltage rises above 95%
(typ) of its nominal regulation voltage. Each PGOOD_
goes low when the corresponding regulator output volt-
age drops below 93.5% (typ) of its nominal regulation volt-
age. Connect a 10kΩ (typ) pullup resistor from PGOOD_
to the relevant logic rail to level-shift the signal. PGOOD_
asserts low during soft-start, and when the buck converter
is disabled.
V
= 2 x V
SUP
OUT
Therefore,
I
LOAD(MAX)
2
I
=
RMS
Choose an input capacitor that exhibits less than +10°C
self-heating temperature rise at the RMS input current for
optimal long-term reliability.
The input-voltage ripple is comprised of ΔV (caused by
Q
the capacitor discharge) and ΔV
of the capacitor). Use low-ESR ceramic capacitors with
high ripple-current capability at the input. The total voltage
(caused by the ESR
ESR
Applications Information
Setting Output Voltage
ripple is the sum of ΔV and ΔV
of an on-cycle. Calculate the input capacitance and ESR
required for a specific ripple using the following equation:
that peaks at the end
Q
ESR
Connect FB1 and FB2 to BIAS to enable fixed buck output
voltages (5V or 3.3V) set by a preset internal resistive
divider connected between OUT1/OUT2 and AGND. To
externally adjust the output voltage between 1V and 14V,
connect a resistive voltage-divider from the converter out-
put (OUT_) to the corresponding FB_ input and then to
∆ V
ESR
ESR [Ω] =
∆ I
P−P
2
(I
+
)
LOAD(MAX)
AGND. Select the bottom-side resistors (R
from
BOTTOM
V
FB_ from FB_-to-AGND) less than or equal to 100kΩ.
OUT
I
X
f
(
)
LOAD(MAX)
V
Calculate the top-side resistors (R from FB_ from
IN
)
TOP
C
[μF] =
IN
( ∆ V
X
output-to-FB_) with the following equation:
Q
SW
R
= R
(V
/V
-1)
TOP
BOTTOM OUT_ FB_
where:
and,
where V
100kΩ.
= V
= 1V R
can be 50kΩ to
FB1
FB2
BOTTOM
(V
−
V
X
)
X
V
IN
OUT
f
OUT
∆ I
=
P − P
V
X L
IN
SW
When an external resistive divider is used to program the
buck output voltage, a feed-forward capacitor in paral-
lel with R
with a low-pF capacitance can be used to
TOP
I
= Maximum output current in A,
LOAD(MAX)
improve control-loop phase margin.
ΔI
= Peak-to-peak inductor current in A,
P-P
Input Capacitor
f
= Switching frequency in MHz,
SW
A 4.7μF ceramic input capacitor is recommended for
proper buck operation. This value can be adjusted based
on application input-voltage-ripple requirements.
L = Inductor value in μH.
Inductor Selection
The input capacitor RMS current requirement (I
defined by the following equation:
) is
RMS
The MAX20457 operates with two switching frequency
options: 2.2MHz and 400kHz. The key parameters on
inductor selection are: inductance value (L), inductor
saturation current (I
minimum required inductance is calculated as:
V
X( V
V
− V
)
OUT
SUPSW_
OUT
√
), and DC resistance (R
SAT
). The
I
= I
X
DCR
RMS
LOAD(MAX)
SUPSW_
I
has a maximum value when the input voltage
RMS
(V − V
IN
)
X
D
OUT
equals twice the output voltage:
L
=
f
MIN
X
I
X
LIR
SW
OUT
Table 1. Buck Converter Inductor and Output Capacitor Selection
BUCK1 INDUCTOR
BUCK1 OUTPUT
CAPACITOR (μF)
BUCK2 INDUCTOR
(μH)
BUCK2 OUTPUT
CAPACITANCE (μF)
SWITCHING
FREQUENCY
(μH)
2.1MHz
400kHz
2.2
10
2 x 22
2 x 47
2.2
10
22
47 + 22
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
where LIR is the ratio of the inductor peak-to-peak AC
current to DC average current, and 0.3 is a typical value
to use.
and minimize the high frequency current loop as small as
possible. Refer to the MAX20457 EV kit for an example
layout. Follow these guidelines for good PCB layout.
See Table 1 for the recommended buck inductors. The
inductor’s saturation current rating must meet or exceed
the LX current limit. For optimum transient response and
highest efficiency, use inductors with a low DC resistance.
Place the input bypass capacitors as close to SUPSW1
and SUPSW2 as possible. The buck input capacitors
deliver high di/dt current pulses when its high-side
MOSFET turns on. Minimize the parasitic inductance in
the power input traces to improve efficiency and reliability.
Output Capacitor
Minimize the connection from the buck output capacitor's
ground terminal to the input capacitor's ground terminal
for each buck regulator. This minimizes the area of cur-
rent loop when the high-side MOSFET is conducting.
The actual capacitance value required relates to the
physical size needed to achieve low ESR, as well as to
the chemistry of the capacitor technology. The capacitor
is usually selected by ESR and the voltage rating rather
than by capacitance value.
Keep buck high-current paths, and power traces wide
and short. Minimize the traces from each buck LX node
to each inductor and from each inductor to the output
capacitors. This minimizes the buck current loop area
and minimizes LX trace resistance and stray capacitance
to achieve optimal efficiency. Using thick copper PCBs (2
ounces vs. 1 ounce) can improve full load efficiency by
1% or more.
When using low capacity filter capacitors, such as ceram-
ic capacitors, size is usually determined by the capac-
ity needed to prevent V
and V
from causing
SAG
SOAR
problems during load transients. Generally, once enough
capacitance is added to meet the overshoot requirement,
undershoot is no longer a problem.
The total voltage sag (V
follows:
) can be calculated as
SAG
Keep all sensitive analog signals (FB1 and FB2) away
from noisy switching nodes (LX_ and BST_) and high
current loops.
2
L
×
( △ I
)
LOAD(MAX)
V
=
+
SAG
Place the BIAS capacitor as close to the BIAS node as
possible. Noise coupling into BIAS can disturb the refer-
ence and bias circuitry if this capacitor is installed away
from the device.
2
×
C
×
(V
×
D
−
V
)
OUT
IN
MAX
OUT
I
×
(t − t)
LOAD(MAX)
C
OUT
Ground is the return path for the full load currents flow-
ing into and out of the MAX20457. It is also the common
reference voltage for all the analog circuits. Improper
ground routing can bring extra resistance and inductance
into the current loop, causing different voltage reference
and worsening voltage ringing or spikes. Place a solid
ground plane layer under the power loop components
layer to shield the switching noise from other sensitive
traces. Connect all the analog ground (AGND) and power
grounds (PGND1, PGND2 and PGND) together at a
single point in a star ground connection. The IC exposed
pad can be the point for ground connection.
The amount of overshoot (V
) during a full-load to
SOAR
no-load transient due to stored inductor energy can be
calculated as:
2
( I
)
× L
LOAD(MAX)
V
=
SOAR
2
×
C
× V
OUT
OUT
See Table 1 for recommended output capacitance.
ESR Considerations
The output capacitor must have low enough equivalent
series resistance (ESR) to meet output ripple and load
transient requirements. When using high-capacitance,
low-ESR capacitors, the ESR of the filter capacitor domi-
nates the output voltage ripple:
The exposed pad under the bottom of the package is
attached with epoxy to the substrate of the IC, making it
an excellent path to remove heat from the IC. Connect
the exposed pad to large ground plane areas through
external or internal layers. Place multiple small vias under
the exposed pad to effectively transfer heat down to the
internal ground plane and the back side of the PCB to
further improve the thermal resistance from the IC pack-
age to the ambient.
V
=
ESR
×
I
×
LIR
RIPPLE(P − P)
LOAD(MAX)
PCB Layout Guidelines
Careful PCB layout is critical to achieve low switching
losses, low EMI, and clean, stable operation. If possible,
mount all power components on the top side of the board,
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Typical Application Circuits
V
/V
BAT OUT1
V
BAT
SUPSW1
PGND1
SUPSW2
PGND2
C
4.7µF
IN2
C
4.7µF
IN1
L1
2.2µH
L2
V
OUT1
V
OUT2
2.2µH
5V/3.5A
3.3V/2A
LX1
LX2
MAX20457
C
47µF
OUT1
C
22µF
OUT2
R
LOAD1
C
0.1µF
C
0.1µF
BST2
BST1
R
LOAD2
BST2
BST1
OUT1
OUT2
FB2
V
BIAS
V
FB1
BIAS
PGOOD1
PGOOD2
V
OUT1
V
BIAS
V
OR µC
BAT
C
EXTVCC
C
BIAS
2.2µF
4.7µF
Figure 1. MAX20457ATIE/VY+ Configuration: 2.1MHz, 5V/3.3V Outputs
V
/V
BAT OU T1
V
BAT
SUPSW1
PGND1
SUPSW2
PGND2
C
4.7µF
IN2
C
4.7µF
IN1
L1
10µH
L2
10µH
V
OU T1
V
OU T2
MAX20457
5V/3.5A
3.3V/2A
LX1
LX2
C
OU T1
C
OU T2
47µF//
22µF
R
LOAD1
C
0.1µF
47µF//
47µF
C
0.1µF
BS T2
BS T1
R
LOAD2
BST2
BST1
OUT1
OUT2
FB2
V
BIAS
V
FB1
BIAS
PGOOD1
PGOOD2
V
OU T1
V
BIAS
V
OR µC
BAT
C
EXTVCC
2.2µF
C
4.7µF
BIAS
Figure 2. MAX20457ATIC/VY+ Configuration: 400kHz, 5V/3.3V Outputs
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
V
/V
BAT OU T1
V
BAT
SUPSW1
PGND1
SUPSW2
PGND2
C
4.7µF
IN2
C
4.7µF
IN1
L1
2.2µH
L2
V
OU T1
V
OU T2
MAX20457
2.2µH
ADJ1/3.5A
AD J2 /2A
LX1
LX2
C
OU T1
C
OU T2
47µF
22µF
R
LOAD1
C
R
LOAD2
C
BS T2
BS T1
0.1µF
0.1µF
R
R
TOP2
TOP1
BST2
BST1
OUT1
OUT2
FB2
FB1
PGOOD1
PGOOD2
R
BOTTOM2
R
BOTTOM1
V
OU T1
V
BIAS
V
OR µC
BAT
C
EXTVCC
2.2µF
C
4.7µF
BIAS
Figure 3. MAX20457ATIE/VY+ Configuration: 2.1MHz ADJ/ADJ Outputs
Ordering Information
V
OPTIONS
OUT
PART NUMBER
SWITCHING FREQUENCY
SPREAD SPECTRUM
(V
/V
) (V)
OUT1 OUT2
MAX20457ATIA/VY+
MAX20457ATIB/VY+
MAX20457ATIC/VY+
MAX20457ATID/VY+
MAX20457ATIE/VY+
MAX20457ATIF/VY+
MAX20457ATIG/VY+
MAX20457ATIH/VY+**
MAX20457ATII/VY+**
3.3/5
2.1MHz
2.1MHz
400kHz
400kHz
2.1MHz
2.1MHz
2.1MHz
2.1MHz
400MHz
Off
On
Off
On
Off
On
On
On
On
3.3/5
5/3.3
5/3.3
5/3.3
5/3.3
3.3/3.3
3.3/3.5
3.3/5
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape-and-reel.
*EP = Exposed pad.
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MAX20457
High-Efficiency, 36V, Dual Synchronous
Buck Converters (3.5A/2A)
for Automotive Applications
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
1/19
Initial release
—
Updated Typical Operating Characteristics, Setting Output Voltage, and Ordering
Information sections
1
2
4/19
7/19
6–7,13, 16
16
Removed all future-part designations from Ordering Information
Updated General Description, Electrical Characteristics, Detailed Description,
Applications Information, and Ordering Information
1, 4, 12, 13,
15, 16
3
11/19
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.
2019 Maxim Integrated Products, Inc.
│ 17
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