EVALUATION KIT AVAILABLE
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MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
General Description
The MAX17634x is a high-efficiency, high-voltage, synchronous step-down DC-DC converter with integrated MOSFETs
operating over an input-voltage range of 4.5V to 36V. It can
deliver up to 4.25A current. The MAX17634 is available in
three variants: MAX17634A, MAX17634B, and MAX17634C.
The MAX17634A and MAX17634B are fixed 3.3V and fixed
5V output voltage parts, respectively. The MAX17634C is
an adjustable output voltage (from 0.9V up to 90% of VIN)
part. Built-in compensation across the output voltage range
eliminates the need for external components.
The MAX17634x features peak-current-mode control
architecture. The device can be operated in forced pulsewidth modulation (PWM), pulse-frequency modulation (PFM),
or discontinuous-conduction mode (DCM) to enable high
efficiency under full-load and lightload conditions. The
MAX17634x offers a low minimum on time that allows high
switching frequencies and a smaller solution size.
The feedback voltage regulation accuracy over -40°C
to +125°C for the MAX17634x is ±1.3%.The device is
available in a compact 20-pin (4mm x 4mm) TQFN package.
Simulation models are available.
Applications
●●
●●
●●
●●
●●
●●
Industrial Control Power Supplies
General-Purpose Point-of-Load
Distributed Supply Regulation
Base Station Power Supplies
Wall Transformer Regulation
High-Voltage, Single-Board Systems
Benefits and Features
●● Reduces External Components and Total Cost
• No Schottky–Synchronous Operation
• Internal Compensation Components
• All-Ceramic Capacitors, Compact Layout
●● Reduces Number of DC-DC Regulators to Stock
• Wide 4.5V to 36V Input
• Adjustable Output Range from 0.9V up to 90% of VIN
• 400kHz to 2.2MHz Adjustable Frequency with
External Synchronization
• Available in a 20-Pin, 4mm x 4mm TQFN Package
●● Reduces Power Dissipation
• Peak Efficiency of 94%
• PFM and DCM Modes Enable Enhanced LightLoad Efficiency
• Auxiliary Bootstrap Supply (EXTVCC) for Improved
Efficiency
• 2.8μA Shutdown Current
●● Operates Reliably in Adverse Industrial Environments
• Hiccup-Mode Overload Protection
• Adjustable and Monotonic Startup with Prebiased
Output Voltage
• Built-in Output-Voltage Monitoring with RESET
• Programmable EN/UVLO Threshold
• Overtemperature Protection
• High Industrial -40°C to +125°C Ambient Operating
Temperature Range/-40°C to +150°C Junction
Temperature Range
Ordering Information appears at end of data sheet.
Typical Application Circuit
EN/UVLO
RT
R5
51.1kΩ
MODE/SYNC
C3
2.2µF
C2
5600pF
INTVCC
SGND
SS
RESET
19-100572; Rev 0; 6/19
IN
C1
2 x 4.7µF
BST
LX
MAX17634B
C5
0.1µF
L1
8.2µH
C4
2 x 47µF
FB
EXTVCC
PGND
VIN
6.5V–36V
VOUT
5V, 4.25A
EP
fSW : 400kHz
L1: 8.2µH (XAL6060-822ME)
C1: 4.7µF/50V/X7R/1206 (GRM31CR71H475KA12)
C4: 47uF/10V/X7R/1210 (GRM32ER71A476ME15)
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Absolute Maximum Ratings
IN to PGND............................................................-0.3V to +40V
EN/UVLO to SGND.....................................-0.3V to (VIN + 0.3V)
LX to PGND................................................-0.3V to (VIN + 0.3V)
EXTVCC to SGND................................................-5.5V to +6.5V
BST to PGND......................................................-0.3V to +46.5V
BST to LX..............................................................-0.3V to +6.5V
BST to INTVCC......................................................-0.3V to +40V
FB to SGND (MAX17634A and MAX17634B)......-5.5V to +6.5V
FB to SGND (MAX17634C)..................................-0.3V to +6.5V
SS, MODE/SYNC, RESET, INTVCC, RT to SGND.....-0.3V to +6.5V
PGND to SGND.....................................................-0.3V to +0.3V
LX Total RMS Current.........................................................±4.7A
Output Short-circuit duration......................................Continuous
Continuous Power Dissipation (Multilayer Board) (TA = +70°C,
derate 38.5mW/°C above +70°C.)...........................3076.9mW
Operating Temperature Range (Note1)................-40°C to 125°C
Junction Temperature........................................ -40°C to +150°C
Storage Temperature Range............................. -65°C to +150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°C
Note 1: Junction temperature greater than +125°C degrades operating lifetimes
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
TQFN
PACKAGE CODE
T2044+4C
Outline Number
21-100172
Land Pattern Number
90-0409
Thermal Resistance, Four-Layer Board (Note 2)
Junction to Ambient (θJA)
26°C/W
Junction to Case (θJC)
2°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.
Note 2: Package thermal resistances were obtained using the MAX17634 evaluation kit with no airflow
www.maximintegrated.com
Maxim Integrated │ 2
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Electrical Characteristics
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2uF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17634A), VFB = 5.5V (MAX17634B), VFB = 1V (MAX17634C), LX = SS = RESET = OPEN, VBST to VLX = 5V,
TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise
noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
36
V
4.5
μA
INPUT SUPPLY (VIN)
Input Voltage Range
Input Shutdown Current
VIN
IIN-SH
4.5
VEN/UVLO = 0V (Shutdown mode)
2.8
MODE/SYNC = OPEN, VEXTVCC = 5V
96
IQ_PFM
RRT = 40.2kΩ, MODE/SYNC = OPEN,
VEXTVCC = 5V
106
IQ_DCM
DCM Mode, VLX = 0.1V
1.2
IQ_PWM
Normal switching mode; VEXTVCC = 5V
11
Input Quiescent Current
μA
1.8
mA
ENABLE/UVLO (EN/UVLO)
EN Threshold
EN Input Leakage Current
VENR
VEN/UVLO rising
1.19
1.215
1.26
VENF
VEN/UVLO falling
1.068
1.09
1.131
VEN/UVLO = 0V, TA = +25°C
-50
0
+50
1mA ≤ IINTVCC ≤ 25mA
4.75
5
5.25
6V ≤ VIN ≤ 36V, IINTVCC = 1mA
4.75
5
5.25
IEN
V
nA
INTVCC (LDO)
INTVCC Output Voltage Range
VINTVCC
INTVCC Current Limit
IINTVCC-MAX
VINTVCC = 4.5V, VIN = 7.5V
INTVCC Dropout
VINTVCC-DO
VIN = 4.5V, IINTVCC = 10mA
INTVCC UVLO
30
V
mA
0.3
VINTVCC_UVR
VINTVCC rising
4.05
4.2
4.3
VINTVCC_UVF
VINTVCC falling
3.65
3.8
3.9
VEXTVCC rising
4.56
4.7
4.84
VEXTVCC falling
4.3
4.43
4.6
V
V
EXTVCC
EXTVCC Switchover Threshold
V
POWER MOSFET
High-Side nMOS On-Resistance
RDS-ONH
ILX = 0.3A, sourcing
60
115
mΩ
Low-Side nMOS On-Resistance
RDS-ONL
ILX = 0.3A, sinking
37
73
mΩ
ILX_LKG
VLX = (VPGND+1) V to (VIN -1) V,
TA = +25°C
3
μA
5.3
μA
LX Leakage Current
-2
SOFT-START (SS)
Charging Current
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ISS
4.7
5
Maxim Integrated │ 3
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2uF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17634A), VFB = 5.5V (MAX17634B), VFB = 1V (MAX17634C), LX = SS = RESET = OPEN, VBST to VLX = 5V,
TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise
noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
MODE/SYNC = SGND or
MODE/SYNC = INTVCC, for MAX17634A
3.256
3.3
3.344
MODE/SYNC = SGND or
MODE/SYNC = INTVCC, for MAX17634B
4.94
5
5.06
MODE/SYNC = SGND or
MODE/SYNC = INTVCC, for MAX17634C
0.888
0.9
0.912
MODE/SYNC = OPEN, for MAX17634A
3.256
3.36
3.44
MODE/SYNC = OPEN, for MAX17634B
4.94
5.09
5.21
MODE/SYNC = OPEN, for MAX17634C
0.889
0.915
0.938
UNITS
FEEDBACK (FB)
FB Regulation Voltage
FB Input Bias Current
VFB-REG
IFB
For MAX17634A
23
For MAX17634B
33
For MAX17634C, TA = +25°C
V
μA
-50
+50
nA
MODE/SYNC
MODE Threshold
SYNC Frequency
Capture Range
VM-DCM
MODE/SYNC = INTVCC (DCM mode)
VM-PFM
MODE/SYNC = OPEN (PFM mode)
VM-PWM
MODE/SYNC = SGND (PWM mode)
FSYNC
fSW set by RRT
SYNC Pulse Width
SYNC Threshold
VINTVCC - 0.65
V
VINTVCC/2
0.75
1.1 x
fSW
1.4 x
fSW
50
VIH
kHz
ns
2.1
VIL
0.8
V
CURRENT LIMIT
Peak Current-Limit Threshold
IPEAK-LIMIT
5.7
6.7
7.7
A
Runaway Current-Limit
Threshold
IRUNAWAY-
6.7
7.8
9
A
PFM Current-Limit Threshold
Valley Current-Limit Threshold
LIMIT
IPFM
IVALLEY-LIMIT
MODE/SYNC = OPEN
MODE/SYNC = OPEN or
MODE/SYNC = INTVCC
MODE/SYNC = SGND
www.maximintegrated.com
1.6
-0.28
0
A
+0.28
A
2.5
Maxim Integrated │ 4
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2uF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17634A), VFB = 5.5V (MAX17634B), VFB = 1V (MAX17634C), LX = SS = RESET = OPEN, VBST to VLX = 5V,
TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise
noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
RRT = 50.8kΩ
380
400
420
RRT = 40.2kΩ
475
500
525
RRT = OPEN
460
500
540
RRT = 8.06kΩ
1950
2200
2450
For MAX17634A
2.03
2.13
2.22
For MAX17634B
3.07
3.22
3.37
For MAX17634C
0.55
0.58
0.605
UNITS
RT
Switching Frequency
VFB Undervoltage Trip Level to
Cause Hiccup
fSW
VFB-HICF
VFB-HICF
HICCUP Timeout
(Note 4)
Minimum On-Time
tON-MIN
Minimum Off-Time
tOFF-MIN
LX Dead TIme
RESET
RESETOutput Level Low
RESETOutput Leakage Current
32768
52
140
LXDT
VRESETL
IRESETLKG
80
ns
160
ns
ns
IRESET = 10mA
-100
V
Cycles
5
TA = TJ = 25°C, VRESET = 5.5V
kHz
400
mV
+100
nA
FB Threshold for RESET
Deassertion
VFB-OKR
VFB Rising, % of VFB-REG
93.8
95
97.8
%
FB Threshold for RESET
Assertion
VFB-OKF
VFB Falling, % of VFB-REG
90.5
92
94.6
%
RESET Delay after FB Reaches
95% Regulation
1024
Cycles
165
°C
10
°C
THERMAL SHUTDOWN (TEMP)
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
Temperature rising
Note 3: Electrical specifications are production tested at TA = +25ºC. Specifications over the entire operating temperature range are
guaranteed by design and characterization.
Note 4: See the Overcurrent Protection/Hiccup Mode Section for more details
www.maximintegrated.com
Maxim Integrated │ 5
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics
((VEN/UVLO = VIN = 24V, VSGND = VPGND = 0V, CINTVCC = 2.2μF, CBST = 0.1μF, CSS = 5600pF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.))
EFFICIENCY vs. LOAD CURRENT
FIGURE 3 AND FIGURE 5 CIRCUITS
100
EFFICIENCY vs. LOAD CURRENT
FIGURE 3 AND FIGURE 5 CIRCUITS
toc01
100
EFFICIENCY vs. LOAD CURRENT
FIGURE 3 AND FIGURE 5 CIRCUITS
toc02
90
90
90
VIN = 24V
VIN = 36V
60
70
60
VIN = 24V
50
30
20
0
1
2
3
4 4.25
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, PWM MODE
60
0.01
0.1
1
4.25
100
4.25
toc06
100
VIN = 6.5V
70
VIN = 24V
VIN = 36V
95
60
EFFICIENCY (%)
VIN = 12V
EFFICIENCY (%)
EFFICIENCY (%)
0.1
1
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, PFM MODE
EFFICIENCY vs. LOAD CURRENT
FIGURE 4 AND FIGURE 6 CIRCUIT
toc05
80
VIN = 36V
70
60
VIN = 24V
50
VIN = 12V
50
0
20
1
2
3
4 4.25
LOAD CURRENT (A)
CONDITIONS: 5V OUTPUT, PWM MODE
80
0.01
0.1
LOAD CURRENT (A)
1
4.25
toc08
3.320
3.305
3.300
3.295
VIN = 24V
VIN = 12V
3.300
3.295
3.290
3.285
3.285
3.280
1
2
3
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, PWM MODE
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4 4.25
VIN = 12V
4.25
VIN = 24V
toc09
3.39
VIN = 36V
3.305
3.290
0
VIN = 4.5V
3.310
OUTPUT VOLTAGE (V)
VIN = 36V
OUTPUT VOLTAGE (V)
VIN = 4.5V
VIN = 36V
0.1
1
LOAD CURRENT (A)
CONDITIONS: 5V OUTPUT, PFM MODE
3.41
3.315
3.315
VIN = 24V
LINE AND LOAD REGULATION
FIGURE 3 AND FIGURE 5 CIRCUITS
LINE AND LOAD REGULATION
FIGURE 3 AND FIGURE 5 CIRCUITS
toc07
3.310
0.01
CONDITIONS: 5V OUTPUT, DCM MODE
LINE AND LOAD REGULATION
FIGURE 3 AND FIGURE 5 CIRCUITS
3.320
VIN = 12V
VIN = 6.5V
VIN = 6.5V
30
fSW = 400kHz
90
85
40
OUTPUT VOLTAGE (V)
0.01
90
80
3.280
VIN = 36V
VIN = 12V
EFFICIENCY vs. LOAD CURRENT
FIGURE 4 AND FIGURE 6 CIRCUIT
toc04
VIN = 24V
VIN = 4.5V
70
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, DCM MODE
90
40
80
VIN = 4.5V
EFFICIENCY vs. LOAD CURRENT
FIGURE 4 AND FIGURE 6 CIRCUITS
100
VIN = 36V
VIN = 12V
40
50
EFFICIENCY (%)
VIN = 12V
VIN = 4.5V
70
EFFICIENCY (%)
EFFICIENCY (%)
80
80
40
toc03
100
VIN = 12V
VIN = 36V
3.37
3.35
VIN = 24V
3.33
3.31
3.29
0
1
2
3
4 4.25
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, DCM MODE
3.27
VIN = 4.5V
0
1
2
3
4 4.25
LOAD CURRENT (A)
CONDITIONS: 3.3V OUTPUT, PFM MODE
Maxim Integrated │ 6
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
((VEN/UVLO = VIN = 24V, VSGND = VPGND = 0V, CINTVCC = 2.2μF, CBST = 0.1μF, CSS = 5600pF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.))
LINE AND LOAD REGULATION
FIGURE 4 AND FIGURE 6 CIRCUITS
toc10
5.020
5.015
VIN = 12V
5.005
5.000
VIN = 6.5V
4.995
5.15
5.010
VIN = 36V
0
5.000
VIN = 6.5V
4.995
1
2
3
LOAD CURRENT (A)
CONDITIONS: 5V OUTPUT, PWM MODE
toc13
VEN/UVLO
5V/div
VIN = 12V
VIN = 24V
5.10
VIN = 36V
5.05
5.00
VIN = 6.5V
0
4 4.25
SOFT-START/SHUTDOWN THROUGH EN/UVLO
FIGURE 3 AND FIGURE 5 CIRCUITS
VIN = 12V
5.005
4.990
4.990
VIN = 24V
OUTPUT VOLTAGE (V)
VIN = 24V
OUTPUT VOLTAGE (V)
VIN = 36V
5.010
toc12
5.20
toc11
5.020
5.015
OUTPUT VOLTAGE (V)
LINE AND LOAD REGULATION
FIGURE 4 AND FIGURE 6 CIRCUITS
LINE AND LOAD REGULATION
FIGURE 4 AND FIGURE 6 CIRCUITS
1
2
3
LOAD CURRENT (A)
CONDITIONS: 5V OUTPUT, DCM MODE
4 4.25
SOFT-START/SHUTDOWN THROUGH EN/UVLO
FIGURE 4 AND FIGURE 6 CIRCUITS
4.95
0
1
2
3
LOAD CURRENT (A)
CONDITIONS: 5V OUTPUT, PFM MODE
SOFT-START WITH PREBIAS OF VOLTAGE 1.65V
FIGURE 3 AND FIGURE 5 CIRCUITS
toc15
toc14
VEN/UVLO
5V/div
4 4.25
VEN/UVLO
5V/div
3.3V
1.65V
2V/div
VOUT
VOUT
2V/div
ILX
2A/div
ILX
2A/div
VRESET
5V/div
VRESET
5V/div
VOUT
2V/div
ILX
2A/div
VRESET
5V/div
1ms/div
1ms/div
1ms/div
CONDITIONS: 3.3V OUTPUT, PWM MODE, 0.776Ω LOAD
CONDITIONS: 5V OUTPUT, PWM MODE, 1.176Ω LOAD
CONDITIONS: 3.3V OUTPUT, PWM MODE, 66Ω LOAD
STEADY-STATE PERFORMANCE
FIGURE 3 AND FIGURE 5 CIRCUITS
STEADY-STATE PERFORMANCE
FIGURE 3 AND FIGURE 5 CIRCUITS
SOFT-START WITH PREBIAS OF VOLTAGE 2.5V
FIGURE 4 AND FIGURE 6 CIRCUITS
toc16
toc17
toc18
5V
VEN/UVLO
5V/div
2.5V
VOUT
2V/div
ILX
2A/div
VRESET
5V/div
1ms/div
CONDITIONS: 5V OUTPUT, PWM MODE, 100Ω LOAD
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VLX
20V/div
VOUT (AC)
20mV/div
5A/div
ILX
20V/div
VLX
VOUT (AC)
10mV/div
0.5A/div
ILX
2µs/div
1µs/div
CONDITIONS: 3.3V OUTPUT, PWM MODE, 4.25A LOAD
CONDITIONS: 3.3V OUTPUT, DCM MODE, 50mA LOAD
Maxim Integrated │ 7
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
((VEN/UVLO = VIN = 24V, VSGND = VPGND = 0V, CINTVCC = 2.2μF, CBST = 0.1μF, CSS = 5600pF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.))
STEADY-STATE PERFORMANCE
FIGURE 3 AND FIGURE 5 CIRCUITS
STEADY-STATE PERFORMANCE
FIGURE 4 AND FIGURE 6 CIRCUITS
toc19
VLX
20V/div
100mV/div
VOUT (AC)
ILX
STEADY-STATE PERFORMANCE
FIGURE 4 AND FIGURE 6 CIRCUITS
toc20
2A/div
toc21
20V/div
VLX
VOUT (AC)
20mV/div
5A/div
ILX
VLX
20V/div
10mV/div
VOUT (AC)
ILX
0.5A/div
100µs/div
2µs/div
1µs/div
CONDITIONS: 3.3V OUTPUT, PFM MODE, 50mA LOAD
CONDITIONS: 5V OUTPUT, PWM MODE, 4.25A LOAD
CONDITIONS: 5V OUTPUT, DCM MODE, 50mA LOAD
LOAD TRANSIENT BETWEEN 0A AND 2A
FIGURE 3 AND FIGURE 5 CIRCUITS
LOAD TRANSIENT BETWEEN 2A AND 4A
FIGURE 3 AND FIGURE 5 CIRCUITS
STEADY-STATE PERFORMANCE
FIGURE 4 AND FIGURE 6 CIRCUITS
toc22
toc23
20V/div
VLX
VOUT (AC)
toc24
50mV/div
VOUT (AC)
50mV/div
100mV/div
VOUT (AC)
4A
2A
ILX
2A/div
1A/div
IOUT
IOUT
2A/div
100µs/div
100µs/div
100µs/div
CONDITIONS: 5V OUTPUT, PFM MODE, 50mA LOAD
CONDITIONS: 3.3V OUTPUT, PWM MODE
CONDITIONS: 3.3V OUTPUT, PWM/PFM/DCM MODE
LOAD TRANSIENT BETWEEN 0.05A AND 2A
FIGURE 3 AND FIGURE 5 CIRCUITS
VOUT (AC)
LOAD TRANSIENT BETWEEN 0A AND 2A
FIGURE 4 AND FIGURE 6 CIRCUITS
LOAD TRANSIENT BETWEEN 0.05A AND 2A
FIGURE 3 AND FIGURE 5 CIRCUITS
toc25
toc27
toc26
100mV/div
VOUT (AC)
1A/div
IOUT
100µs/div
CONDITIONS: 3.3V OUTPUT, DCM MODE
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100mV/div
VOUT (AC)
50mV/div
1A/div
IOUT
400µs/div
CONDITIONS: 3.3V OUTPUT, PFM MODE
IOUT
1A/div
100µs/div
CONDITIONS: 5V OUTPUT, PWM MODE
Maxim Integrated │ 8
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
((VEN/UVLO = VIN = 24V, VSGND = VPGND = 0V, CINTVCC = 2.2μF, CBST = 0.1μF, CSS = 5600pF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.))
LOAD TRANSIENT BETWEEN 2A AND 4A
FIGURE 4 AND FIGURE 6 CIRCUITS
toc28
VOUT (AC)
LOAD TRANSIENT BETWEEN 0.05A AND 2A
FIGURE 4 AND FIGURE 6 CIRCUITS
LOAD TRANSIENT BETWEEN 0.05A AND 2A
FIGURE 4 AND FIGURE 6 CIRCUITS
toc30
toc29
100mV/div
100mV/div
VOUT (AC)
VOUT (AC)
100mV/div
4A
2A
IOUT
2A/div
1A/div
IOUT
1A/div
IOUT
100µs/div
100µs/div
200µs/div
CONDITIONS: 5V OUTPUT, PWM/PFM/DCM MODE
CONDITIONS: 5V OUTPUT, DCM MODE
CONDITIONS: 5V OUTPUT, PFM MODE
SHORT-CIRCUIT PROTECTION
FIGURE 4 AND FIGURE 6 CIRCUITS
OVERLOAD PROTECTION
FIGURE 4 AND FIGURE 6 CIRCUITS
SHORT-CIRCUIT PROTECTION
FIGURE 3 AND FIGURE 5 CIRCUITS
100mV/div
VOUT
ILX
2A/div
40ms/div
CONDITIONS: 3.3V OUTPUT, PWM MODE, R_LOAD = 0.01Ω
VOUT
100mV/div
ILX
VLX
2A/div
40ms/div
CONDITIONS: 5V OUTPUT, PWM MODE, R_LOAD = 0.35Ω
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 4 AND FIGURE 6 CIRCUITS
toc35
20V/div
20mV/div
ILX
ILX
40ms/div
5V/div
VOUT (AC)
1V/div
CONDITIONS: 5V OUTPUT, PWM MODE, R_LOAD = 0.01Ω
toc34
VSYNC
VOUT
2A/div
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 3 AND FIGURE 5 CIRCUITS
5A/div
10µs/div
CONDITIONS: 3.3V OUTPUT, PWM MODE, 4.25A LOAD
fSW = 400kHz, EXTERNAL CLOCK FREQUENCY = 440kHz
www.maximintegrated.com
toc33
toc32
toc31
VSYNC
VLX
VOUT (AC)
ILX
5V/div
20V/div
50mV/div
5A/div
10µs/div
CONDITIONS: 5V OUTPUT, PWM MODE, 4.25A LOAD
fSW = 400kHz, EXTERNAL CLOCK FREQUENCY = 440kHz
Maxim Integrated │ 9
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
((VEN/UVLO = VIN = 24V, VSGND = VPGND = 0V, CINTVCC = 2.2μF, CBST = 0.1μF, CSS = 5600pF, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to SGND, unless otherwise noted.))
MAX17634A BODE PLOT
FIGURE 5 CIRCUIT
MAX17634B BODE PLOT
FIGURE 6 CIRCUIT
PHASE
PHASE
60
30
60
20
40
20
40
10
20
10
20
0
0
GAIN
-20
0
-40
-20
-30
-60
-30
-80
-40
-50
-50
-100
300k
1k
0
GAIN
-10
-20
GAIN CROSS OVER FREQUENCY = 51.8kHz
PHASE MARGIN = 62.3 ˚
80
10k
100k
FREQUENCY (Hz)
CONDITIONS: FIXED 3.3V OUTPUT, 4.25A LOAD, PWM MODE
-20
-40
-60
GAIN CROSS OVER FREQUENCY = 50.2kHz
PHASE MARGIN = 65.5 ˚
1k
-80
-100
300k
10k
100k
FREQUENCY (Hz)
CONDITIONS: FIXED 5V OUTPUT, 4.25A LOAD, PWM MODE
MAX17634C BODE PLOT
FIGURE 4 CIRCUIT
MAX17634C BODE PLOT
FIGURE 3 CIRCUIT
toc38
toc39
40
30
60
30
60
20
40
20
40
10
20
10
20
0
0
GAIN
-10
-20
GAIN (dB)
50
80
PHASE
40
PHASE (˚)
100
50
-20
-30
-60
-30
-80
-40
GAIN CROSS OVER FREQUENCY = 50.2kHz
PHASE MARGIN = 62.9 ˚
-50
1k
-50
-100
300k
10k
100k
FREQUENCY (Hz)
CONDITIONS: ADJUSTABLE 3.3V OUTPUT, 4.25A LOAD, PWM MODE
0
GAIN
-10
-40
100
80
0
-20
-40
PHASE
-20
PHASE (˚)
-10
GAIN (dB)
30
PHASE (˚)
40
-40
GAIN (dB)
100
80
40
GAIN (dB)
toc37
50
100
PHASE (˚)
toc36
50
-40
-60
GAIN CROSS OVER FREQUENCY = 51.5kHz
PHASE MARGIN = 64.6 ˚
1k
10k
100k
FREQUENCY (Hz)
-80
-100
300k
CONDITIONS: ADJUSTABLE 5V OUTPUT, 4.25A LOAD, PWM MODE
TUV Rheinland
Final_ScanV
MaximIC_MAX17634_24VIN_5VOUT
FinaL_ScanH
MAX17634C,
5V OUTPUT, 4.25A LOAD CURRENT
RE 30MHz-1GHz
Limittoc41
RADIATED EMI CURVE
50
50.0
Am p litu d e (d Bu V /m )
MAGNITUDE (dBµV/m)
40.0
40
CISPR-22 CLASS B QP LIMIT
30
30.0
20.0
20
10.0
10
VERTICAL SCAN
00
HORIZONTAL SCAN
-10.0
-10
30.0M
30
100.0M
100
1.0G
1000
Frequency (Hz) (MHz)
FREQUENCY
RE 30MHz-1GHz_0-360deg_90deg
step_1-4mtr Height_Quick
CONDITIONS: MEASURED
ON THEScan_Test7.TIL
MAX17634CEVKIT
08:16:02 PM, Monday, November 26, 2018
www.maximintegrated.com
Maxim Integrated │ 10
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
IN
NC
EXTVCC
MODE/SYNC
TOP VIEW
PGND
Pin Configuration
15
14
13
12
11
NC 16
MAX17634A
MAX17634B
MAX17634C
LX 17
LX 18
LX 19
*EP
*EXPOSED PAD
3
4
RT
9
FB
8
SS
7
SGND
6
INTVCC
5
RESET
2
EN/UVLO
PGND
1
IN
+
IN
BST 20
10
20-PIN TQFN
(4mm x 4mm)
Pin Description
PIN
NAME
1, 15
PGND
2,3,14
IN
Power-Supply Input Pins. 4.5V to 36V input supply range. Decouple to PGND with a minimum of
4.7μF capacitor; place the capacitor close to the IN and PGND pins.
4
EN/UVLO
Enable/Undervoltage Lockout Pin. Drive EN/UVLO high (greater than VENR) to enable the output.
Connect to the center of the resistor-divider between IN and SGND to set the input voltage at
which the part turns on. Connect to IN pin for always on operation. Pull low (lower than VENF) for
disabling the device.
5
RESET
Open-Drain RESET Output. The RESEToutput is driven low if FB drops below 92% of its set value.
RESET goes high 1024 cycles after FB rises above 95% of its set value
6
INTVCC
5V LDO Output of the Part. Bypass INTVCC with a 2.2μF ceramic capacitance to SGND.
LDO doesn't support the external loading on INTVCC.
7
SGND
8
SS
www.maximintegrated.com
FUNCTION
Power Ground Pins of the Converter. Connect externally to the power ground plane.
Refer to the MAX17634 EV kit data sheet for a layout example.
Analog Ground
Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time.
Maxim Integrated │ 11
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Pin Description (continued)
PIN
NAME
FUNCTION
9
FB
Feedback Input. Connect the output voltage node (VOUT) to FB for MAX17634A and MAX17634B.
Connect FB to the center node of an external resistor-divider from the output to SGND to set the
output voltage for MAX17634C. See the Adjusting Output Voltage section for more details.
10
RT
Programmable Switching Frequency Input. Connect a resistor from RT to SGND to set the
regulator’s switching frequency between 400kHz and 2.2MHz. Leave RT open for the default
500kHz frequency. See the Setting the Switching Frequency (RT) for more details.
MODE/SYNC Pin Configures the Device to Operate in PWM, PFM, or DCM Modes of Operation.
Leave MODE/SYNC open for PFM operation (pulse skipping at light loads).
Connect MODE/SYNC to SGND for constant-frequency PWM operation at all loads. Connect
MODE/SYNC to INTVCC for DCM operation at light loads.The device can be synchronized to an
external clock using this pin. See the Mode Selection and External Clock Synchronization (MODE/
SYNC) section for more details.
11
MODE/SYNC
12
EXTVCC
13,16
NC
No Connection
17-19
LX
Switching Node Pins. Connect LX pins to the switching side of the inductor.
20
BST
—
EP
www.maximintegrated.com
External Power Supply Input Reduces the Internal-LDO loss. Connect it to buck output when it is
programmed to 5V only. When EXTVCC is not used, connect it to SGND.
Boost Flying Capacitor. Connect a 0.1μF ceramic capacitor between BST and LX.
Exposed Pad. Always connect EP to the SGND pin of the IC. Also, connect EP to a large SGND
plane with several thermal vias for best thermal performance. Refer to the MAX17634 EV kit data
sheet for an example of the correct method for EP connection and thermal vias.
Maxim Integrated │ 12
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Functional Diagram
MAX17634A
MAX17634B
MAX17634C
EXTVCC
INTVCC
BST
LDO
IN
SGND
CURRENT-SENSE
LOGIC
EN/UVLO
ENOK
1.215V
HICCUP
LX
PWM/PFM/HICCUP
LOGIC
RT
OSCILLATOR
PGND
*S1
FB
*S2
*S3
R1
ERROR AMPLIFI ER/
LOOP COMPENSATION
THERMAL
SHUTDOW N
R2
SLOPE
COMPENSATI ON
INTVCC
SWITCH OVER LOGIC
MODE
SELE CTION
LOGIC
SS
HICCUP
*S1 - CLOSE, *S2,*S3 - OPEN FOR MA X17634C
*S1 - OPEN, *S2,*S3 - CLOSE FOR MAX17634A/MAX17634B
R1 – 132.7kΩ, R2 – 29.1kΩ FOR MAX17634B
R1 – 104kΩ, R2 – 38.8kΩ FOR MAX17634A
www.maximintegrated.com
ENOK
FB
MODE/
SYNC
RESET
RESET
LOGIC
Maxim Integrated │ 13
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Detailed Description
The MAX17634x is a high-efficiency, high-voltage,
synchronous step-down DC-DC converter with
integrated MOSFETs operating over an input voltage
range of 4.5V to 36V. It can deliver up to 4.25A current.
The MAX17634A and MAX17634B are the fixed 3.3V
and fixed 5V output parts, respectively. The MAX17634C
is an adjustable output voltage (from 0.9V upto 90% of
VIN) part. Built-in compensation across the output voltage
range eliminates the need for external compensation
components. The feedback (FB) voltage regulation
accuracy over -40°C to +125°C is ±1.3% for MAX17634x.
The device features a peak-current-mode control
architecture. An internal transconductance error amplifier
produces an integrated error voltage at an internal node,
which sets the duty cycle using a PWM comparator, a
high-side current-sense amplifier, and a slope-compensation generator. At each rising edge of the clock, the
highside MOSFET turns on and remains on until either
the appropriate or maximum duty cycle is reached, or
the peak current limit is detected. During the high-side
MOSFET’s on-time, the inductor current ramps up. During
the second half of the switching cycle, the high-side
MOSFET turns off and the low-side MOSFET turns on.
The inductor releases the stored energy as its current
ramps down and provides current to the output.
The device features a MODE/SYNC pin that can be
used to operate the device in PWM, PFM, or DCM
control schemes. The device also features adjustableinput undervoltage lockout, adjustable soft-start, open
drain RESET, and external frequency synchronization
features. The MAX17634x offers a low minimum on time
that enables to design converter at higher switching frequencies and a small solution size.
Mode Selection and External Clock
Synchronization (MODE/SYNC):
The MAX17634x supports the PWM, PFM, and DCM
modes of operation. The device enters the required
mode of operation based on the setting of the MODE/
SYNC pin as detected within 1.5ms after INTVCC and
EN/UVLO voltages exceed their respective UVLO rising
thresholds (VINTVCC-UVR, VENR). If the MODE/SYNC pin
is open, the device operates in PFM mode at light loads.
If the state of the MODE/SYNC pin is low (< VM-PWM),
the device operates in constant-frequency PWM mode
at all loads. If the state of the MODE/SYNC pin is high
(>VM-DCM), the device operates in DCM mode at light
loads.
www.maximintegrated.com
During external clock synchronization the device operates
in PWM mode, irrespective of whether PWM or DCM
mode is set. When 16 external clock rising edges are
detected on the MODE/SYNC pin, the internal oscillator frequency set by RT pin (fSW) changes to external
clock frequency. The device remains in PWM mode until
EN/UVLO or input power is cycled. The external clock
frequency must be between 1.1 x fSW and 1.4 x fSW. The
minimum external clock pulse width should be greater
than 50ns. The off-time duration of the external clock
should be at least 160ns.
If PFM mode of operation is set, the device ignores the
external clock pulses and remains in PFM mode. Thus,
external clock synchronization is not supported in PFM
mode.
See the MODE/SYNC section
Characteristics table for details.
of
the
Electrical
PWM Mode Operation
In PWM mode, the inductor current is allowed to go
negative. PWM operation provides constant frequency
operation irrespective of loading, and is useful in applications sensitive to switching frequency. However, the PWM
mode of operation gives lower efficiency at light loads
compared to PFM and DCM modes of operation.
PFM Mode Operation
PFM mode of operation disables negative inductor
current and additionally skips pulses at light loads for high
efficiency. In PFM mode, the inductor current is forced to
a fixed peak of IPFM (1.6A, typ) every clock cycle until
the output rises to 102.3% of the set nominal output
voltage. Once the output reaches 102.3% of the set
nominal output voltage, both the high-side and low-side
FETs are turned off and the device enters hibernate
operation until the load discharges the output to 101.1%
of the set nominal output voltage. Most of the internal
blocks are turned off in hibernate operation to save
quiescent current. After the output falls below 101.1% of
the set nominal output voltage, the device comes out of
hibernate operation, turns on all internal blocks, and again
commences the process of delivering pulses of energy
to the output until it reaches 102.3% of the set nominal
output voltage. The advantage of the PFM mode is
higher efficiency at light loads because of lower quiescent
current drawn from the supply. The disadvantage is that
the output-voltage ripple is higher compared to PWM or
DCM modes of operation and switching frequency is not
constant at light loads.
Maxim Integrated │ 14
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
DCM Mode Operation
DCM mode of operation features constant frequency
operation down to lighter loads than PFM mode, by
disabling negative inductor current at light loads. DCM
operation offers efficiency performance that lies between
PWM and PFM modes. The output voltage ripple in DCM
mode is comparable to PWM mode and relatively lower
compared to PFM mode.
Linear Regulator (INTVCC and EXTVCC)
The MAX17634x has an internal LDO (low dropout)
regulator that powers INTVCC from IN. This LDO is
enabled during power-up or when EN/UVLO is above
0.75V (typ). An internal switch connects the EXTVCC to
INTVCC. The switch is open during power up. If INTVCC
is above its UVLO threshold and, if EXTVCC is greater
than 4.7V (typ), the internal LDO is disabled and INTVCC
is powered from EXTVCC. Powering INTVCC from
EXTVCC increases efficiency at higher input voltages.
Typical INTVCC output voltage is 5V. Bypass INTVCC to
SGND with a 2.2µF low-ESR ceramic capacitor. INTVCC
powers the internal blocks and the low-side MOSFET
driver and recharges the external bootstrap capacitor.
The MAX17634x employs an undervoltage lockout circuit
that forces the buck converter off when INTVCC falls below
VINTVCC-UVF (3.8, typ). The buck converter can be immediately enabled again when INTVCC > VINTVCC-UVR (4.2,
typ). The 400mV UVLO hysteresis prevents chattering on
power-up/power-down.
In applications where the buck converter output is
connected to EXTVCC pin, if the output is shorted to
ground then the transfer from EXTVCC to internal LDO
happens seamlessly without any impact on the normal
functionality. Connect the EXTVCC pin to SGND, when
not in use.
Setting the Switching Frequency (RT)
The switching frequency of the device can be
programmed from 400kHz to 2.2MHz by using a resistor
connected from the RT pin to SGND. The switching
frequency (fSW) is related to the resistor (RRT) connected
at the RT pin by the following equation:
21000
RRT ≅ f
− 1.7
SW
www.maximintegrated.com
Where RRT is in kΩ and fSW is in kHz. Leaving the RT pin
open will force the device to operate at default switching
frequency of 500kHz. See Table 1 for RRT resistor values
for a few common switching frequencies.
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage setting should be calculated as
follows:
Where
VOUT = Steady-state output voltage,
IOUT(MAX) = Maximum load current,
RDCR = Worst-case DC resistance of the inductor,
fSW(MAX) = Maximum switching frequency,
tOFF-MIN(MAX) = Worst-case minimum switch off-time
(160ns),
tON-MIN(MAX) =Worst-case minimum switch on-time
(80ns),
RDS-ONL(MAX) and RDS-ONH(MAX) = Worst-case onstate resistances of low-side and high-side internal
MOSFETs, respectively.
Table 1. Switching Frequency vs.
RRT Resistor
SWITCHING FREQUENCY
(kHz)
R RT RESISTOR (kΩ)
400
50.8
500
OPEN
500
40.2
2200
8.06
Maxim Integrated │ 15
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Overcurrent Protection/Hiccup Mode
The device is provided with a robust overcurrent protection
(OCP) scheme that protects the device under overload
and output short-circuit conditions. A cycle-by-cycle peak
current limit turns off the high-side MOSFET whenever
the high-side switch current exceeds an internal limit
of IPEAK-LIMIT (6.7A, typ). A runaway current limit on
the high-side switch current at IRUNAWAY-LIMIT (7.8A,
typ) protects the device under high input voltage, output short-circuit conditions when there is insufficient
output voltage available to restore the inductor current
that was built up during the on period of the step-down
converter. One occurrence of the runaway current limit
triggers a hiccup mode. In addition, if feedback voltage
drops to VFB-HICF due to a fault condition, hiccup mode
is triggered 1024 clock cycles after soft-start time is
completed. In hiccup mode, the converter is protected
by suspending switching for a hiccup timeout period of
32,768 clock cycles of half the switching frequency. Once
the hiccup timeout period expires, soft-start is attempted
again. Note that when soft-start is attempted under
overload condition, if feedback voltage does not exceed
VFB-HICF, the device continues to switch at half the
programmed switching frequency for the time duration of
the programmed soft-start time and 1024 clock cycles.
Hiccup mode of operation ensures low power dissipation
under output short-circuit conditions.
RESET Output
The device includes a RESET comparator to monitor
the status of output voltage. The open-drain RESET
output requires an external pullup resistor. RESET goes
high (high impedance) with a delay of 1024 switching
cycles after the regulator output increases above 95%
(VFB-OKR) of VFB-REG. RESET goes low when the
regulator output voltage drops to below 92% (VFB-OKF) of
VFB-REG. RESET also goes low during thermal shutdown
or when EN/UVLO pin goes below VENF.
Prebiased Output
When the device starts into a prebiased output, both the
high-side and the low-side switches are turned off so that
the converter does not sink current from the output. Highside and low-side switches do not start switching until
the PWM comparator commands the first PWM pulse, at
which point switching commences. The output voltage is
then smoothly ramped up to the target value in alignment
with the internal reference.
www.maximintegrated.com
Thermal-Shutdown Protection
Thermal-shutdown protection limits junction temperature
in the device. When the junction temperature of the device
exceeds +165°C, an on-chip thermal sensor shuts down
the device, allowing the device to cool. The device turns
on with soft-start after the junction temperature reduces
by 10°C. Carefully evaluate the total power dissipation
(see the Power Dissipation section) to avoid unwanted
triggering of the thermal shutdown in normal operation.
Applications Information
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor RMS current requirement (IRMS) is
defined by the following equation:
IRMS = IOUT(MAX) ×
√VOUT ×(
VIN - VOUT )
VIN
where, IOUT(MAX) is the maximum load current. IRMS has
a maximum value when the input voltage equals twice
the output voltage (VIN = 2 x VOUT), so IRMS(MAX) =
IOUT(MAX)/2. Choose an input capacitor that exhibits less
than +10°C temperature rise at the RMS input current for
optimal long-term reliability. Use low-ESR ceramic capacitors with high-ripple-current capability at the input. X7R
capacitors are recommended in industrial applications for
their temperature stability. Calculate the input capacitance
using the following equation:
CIN
=
(
IOUT MAX × D × 1 − D
(
)
η × fSW × ∆ VIN
)
where,
D = VOUT/VIN is the duty ratio of the converter,
fSW = Switching frequency,
ΔVIN = Allowable input voltage ripple,
η = Efficiency.
In applications where the source is located distant from
the device input, an appropriate electrolytic capacitor
should be added in parallel to the ceramic capacitor
to provide necessary damping for potential oscillations
caused by the inductance of the longer input power path
and input ceramic capacitor.
Maxim Integrated │ 16
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Inductor Selection
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (ISAT) and DC resistance (RDCR). The
switching frequency and output voltage determine the
inductor value as follows:
L =
0.7 x VOUT
fSW
where VOUT and fSW are nominal values and fSW is in
Hz. Select an inductor whose value is nearest to the value
calculated by the previous formula. Select a low-loss
inductor closest to the calculated value with acceptable
dimensions and having the lowest possible DC
resistance. The saturation current rating (ISAT) of the
inductor must be high enough to ensure that saturation
can occur only above the peak current-limit value of
IPEAK-LIMIT (6.7A, typ).
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to
their stability over temperature in industrial applications.
Output capacitor is calculated and sized to support a
50% of maximum output current as the dynamic step
load, and to contain the output voltage deviation to within
±3% of the output voltage. The minimum required output
capacitance can be calculated as follows:
1
COUT = 2 ×
ISTEP × tRESPONSE
∆ VOUT
tRESPONSE ≅
0.35
fC
where,
ISTEP = Load current step,
tRESPONSE = Response time of the controller,
ΔVOUT = Allowable output-voltage deviation,
Soft-Start Capacitor Selection
The device implements adjustable soft-start operation to
reduce inrush current. A capacitor connected from the SS pin
to SGND programs the soft-start time. The selected output
capacitance (CSEL) and the output voltage (VOUT) determine
the minimum required soft-start capacitor as follows:
CSS ≥ 28 × 10−6 × CSEL × VOUT
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
tSS =
CSS
5.55 × 10−6
For example, to program a 1ms soft-start time, a 5.6nF
capacitor should be connected from the SS pin to SGND.
Note that, during startup, the device operates at half the
programmed switching frequency until the output voltage
reaches 64.4% of set output nominal voltage.
Setting the Input Undervoltage-Lockout Level
The device offers an adjustable input undervoltagelockout level. Set the voltage at which the device turns
on with a resistive voltage-divider connected from INto
SGND (see Figure 1). Connect the center node of the
divider to EN/UVLO. Choose RTOP to be 3.3MΩ and then
calculate RBOTTOM as follows:
RBOTTOM =
RTOP × 1.215
(VINU − 1.215)
where VINU is the voltage at which the device is required
to turn on. Ensure that VINU is higher than 0.8 x VOUT
to avoid hiccup during slow power-up (slower than softstart)/ power-down. If the EN/UVLO pin is driven from an
external signal source, a series resistance of minimum
1kΩ is recommended to be placed between the output pin
of signal source and the EN/UVLO pin, to reduce voltage
ringing on the line.
fC = Target closed-loop crossover frequency,
fSW = Switching frequency.
Select fC to be 1/10th of fSW for the switching frequencies
less than or equal to 800 kHz. If the switching frequency
is more than 800 kHz, select fC to be 80kHz. Actual derating of ceramic capacitors with DC bias voltage must be
considered while selecting the output capacitor. Derating
curves are available from all major ceramic capacitor
manufacturers.
VIN
MAX17634A
MAX17634B
MAX17634C
RTOP
EN/UVLO
RBOTTOM
Figure 1. Setting the Input Undervoltage Lockout
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Maxim Integrated │ 17
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Adjusting Output Voltage
Set the output voltage with a resistive voltage-divider
connected from the output-voltage node (VOUT) to SGND
(see Figure 2). Connect the center node of the divider
to the FB pin for MAX17634C. Connect the output
voltage node (VOUT) to the FB pin for MAX17634A and
MAX17634B. Use the following procedure to choose the
resistive voltage-divider values:
Calculate resistor RU from the output to the FB pin as
follows:
320
RU = f × C
C
OUT_SEL
VOUT
MAX17634C
RU
FB
RB
Figure 2. Setting the Output Voltage
For a typical multilayer board, the thermal performance
metrics for the package are given below:
where,
θJA = 26ºC/W
RU is in kΩ,
θJC = 2ºC/W
fC = Crossover frequency is in Hz,
COUT_SEL= Actual capacitance of selected output capacitor
at DC-bias voltage in F.
Calculate resistor RB connected from the FB pin to SGND
as follows:
RB =
RU × 0.9
(VOUT − 0.9)
RB is in kΩ.
Select an appropriate fC and COUT, so that the parallel
combination of RB and RU is less than 50kΩ.
Power Dissipation
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as
follows:
(
( 1 )) (
PLOSS = POUT × η − 1 − IOUT2 × RDCR
)
POUT = VOUT × IOUT
where,
POUT = Output power,
η = Efficiency of the converter.
RDCR = DC resistance of the inductor (see the Typical
Operating Characteristics for more information on
efficiency at typical operating conditions).
www.maximintegrated.com
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA(MAX))
from the following equation:
TJ(MAX) = TA(MAX) + (θJA × PLOSS)
If the application has a thermal-management system that
ensures that the exposed pad of the device is maintained
at a given temperature (TEP(MAX)) by using proper heat
sinks, then the junction temperature of the device can be
estimated at any given maximum ambient temperature as:
TJ(MAX) = TEP(MAX) + (θJC × PLOSS)
Note: Junction temperatures greater than +125°C
degrades operating lifetimes.
PCB Layout Guidelines
All connections carrying pulsed currents must be very
short and as wide as possible. The inductance of these
connections must be kept to an absolute minimum due
to the high di/dt of the currents. Since inductance of a
current carrying loop is proportional to the area enclosed
by the loop, if the loop area is made very small,
inductance is reduced. Additionally, small-current loop
areas reduce radiated EMI.
A ceramic input filter capacitor should be placed close
to the IN pins of the IC. This eliminates as much trace
inductance effects as possible and gives the IC a cleaner
voltage supply. A bypass capacitor for the INTVCC pin
also should be placed close to the pin to reduce effects of
trace impedance.
Maxim Integrated │ 18
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
When routing the circuitry around the IC, the analog small
signal ground and the power ground for switching currents
must be kept separate. They should be connected together
at a point where switching activity is at a minimum. This
helps keep the analog ground quiet. The ground plane
should be kept continuous/unbroken as far as possible.
No trace carrying high switching current should be placed
directly over any ground plane discontinuity.
PCB layout also affects the thermal performance of the
design. A number of thermal throughputs that connect to a
large ground plane should be provided under the exposed
pad of the part, for efficient heat dissipation.
For a sample layout that ensures first pass success,
refer to the MAX17634 evaluation kit layout available at
www.maximintegrated.com.
Typical Application Circuits
Adjustable 3.3V Output Typical Application Circuit
VIN
4.5V–36V
C1
2x4.7µF
EN/UVLO
IN
RT
R5
51.1kΩ
IN
IN
LX
INTVCC
C3
2.2µF
MAX17634C
C5
0.1µF
RESET
L1
5.6µH
VOUT
3.3V, 4.25A
LX
LX
SGND
SS
MODE/SYNC:
1.CONNECT TO SGND FOR PWM MODE
2.CONNECT TO INTVCC FOR DCM MODE
3.LEAVE OPEN FOR PFM MODE
BST
MODE/SYNC
fSW : 400kHz
L1: 5.6µH (XAL6060-562ME)
C1: 4.7µF/50V/X7R/1206 (GRM31CR71H475KA12)
C4: 47µF/10V/X7R/1210 (GRM32ER71A476ME15)
C4
2x47µF
R1
105kΩ
FB
PGND
PGND
EXTVCC
C2
5600pF
R2
39.2kΩ
Figure 3. Adjustable 3.3V Output with 400kHz Switching Frequency
www.maximintegrated.com
Maxim Integrated │ 19
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Application Circuits (continued)
Adjustable 5V Output Typical Application Circuit
VIN
6.5V-36V
C1
2x4.7µF
EN/UVLO
IN
IN
RT
R5
51.1kΩ
IN
C5
0.1µF
LX
INTVCC
C3
2.2µF
MODE/SYNC:
1.CONNECT TO SGND FOR PWM MODE
2.CONNECT TO INTVCC FOR DCM MODE
3.LEAVE OPEN FOR PFM MODE
BST
MODE/SYNC
MAX17634C
L1
8.2µH
VOUT
LX
RESET
5V, 4.25A
C4
2x47µF
LX
SGND
R1
133kΩ
FB
PGND
SS
fSW : 400kHz
L1: 8.2µH (XAL6060-822ME)
C1: 4.7µF/50V/X7R/1206 (GRM31CR71H475KA12)
C4: 47µF/10V/X7R/1210 (GRM32ER71A476ME15)
EXTVCC
PGND
C2
5600pF
R2
29.4kΩ
VOUT
Figure 4. Adjustable 5V Output with 400kHz Switching Frequency
Fixed 3.3V Output Typical Application Circuit
EN/UVLO
IN
RT
R5
51.1kΩ
IN
C1
2x4.7µF
IN
BST
MODE/SYNC
LX
INTVCC
C3
2.2µF
MAX17634A
LX
LX
SGND
RESET
SS
VIN
4.5V–36V fSW : 400kHz
L1: 5.6µH (XAL6060-562ME)
C1: 4.7µF/50V/X7R/1206 (GRM31CR71H475KA12)
C4: 47µF/10V/X7R/1210 (GRM32ER71A476ME15)
C5
0.1µF
L1
5.6µH
MODE/SYNC:
1.CONNECT TO SGND FOR PWM MODE
2.CONNECT TO INTVCC FOR DCM MODE
3.LEAVE OPEN FOR PFM MODE
VOUT
3.3V, 4.25A
C4
2x47µF
FB
PGND
PGND
EXTVCC
C2
5600pF
Figure 5. Fixed 3.3V Output with 400kHz Switching Frequency
www.maximintegrated.com
Maxim Integrated │ 20
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Application Circuits (continued)
Fixed 5V Output Typical Application Circuit
VIN
6.5V-36V fSW : 400kHz
L1: 8.2µH (XAL6060-822ME)
C1: 4.7µF/50V/X7R/1206 (GRM31CR71H475KA12)
C4: 47µF/10V/X7R/1210 (GRM32ER71A476ME15)
C1
2x4.7µF
EN/UVLO
IN
IN
IN
RT
R5
51.1kΩ
BST
MODE/SYNC
LX
INTVCC
C3
2.2µF
MAX17634B
L1
8.2µH
MODE/SYNC:
1.CONNECT TO SGND FOR PWM MODE
2.CONNECT TO INTVCC FOR DCM MODE
3.LEAVE OPEN FOR PFM MODE
LX
LX
SGND
RESET
SS
C5
0.1µF
C4
2x47µF
VOUT
5V, 4.25A
FB
PGND
PGND
EXTVCC
C2
5600pF
Figure 6. Fixed 5V Output with 400kHz Switching Frequency
Ordering Information
PART NUMBER
OUTPUT
VOLTAGE(V)
PIN-PACKAGE
MAX17634AATP+
3.3
20 TQFN 4mm x 4mm
MAX17634BATP+
5
20 TQFN 4mm x 4mm
MAX17634CATP+
Adjustable
20 TQFN 4mm x 4mm
+Denotes a lead(Pb)-free/RoHS compliant package.
www.maximintegrated.com
Maxim Integrated │ 21
MAX17634A/MAX17634B/
MAX17634C
4.5V to 36V, 4.25A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/19
DESCRIPTION
Initial release
PAGES
CHANGED
—
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.
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