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MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
General Description
The Himalaya series of voltage regulator ICs, power modules, and chargers enable cooler, smaller, and simpler
power supply solutions. The MAX17633 is a high-efficiency, high-voltage, Himalaya 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 3.5A current. The MAX17633 is available in three
variants MAX17633A, MAX17633B, and MAX17633C.
The MAX17633A and MAX17633B are the fixed 3.3V and
fixed 5V output voltage parts, respectively. MAX17633C
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 MAX17633 features peak-current-mode control architecture. The device can be operated in forced pulse-width
modulation (PWM), pulse-frequency modulation (PFM),
or discontinuous-conduction mode (DCM) to enable high
efficiency under full-load and light-load conditions.
The feedback-voltage-regulation accuracy over -40°C
to +125°C for the MAX17633A, MAX17633B, and
MAX17633C is ±1.3%. 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
• Delivers up to 3.5A Over the Temperature Range
• 400kHz to 2.2MHz Adjustable Frequency with
External Clock Synchronization
• Available in a 20-Pin, 4mm × 4mm TQFN Package
●● Reduces Power Dissipation
• Peak Efficiency > 93%
• 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
• CISPR 22 Class B Compliant
• Wide -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
RT
EN/UVLO
MODE/SYNC
C3
2.2µF
C2
5600pF
19-100305; Rev 2; 7/20
SGND
RESET
BST
LX
INTVCC
SS
IN
MAX17633B
C5
0.1µF
L1
6.8µH
C4
2 x 22µF
EXTVCC
FB
PGND
VIN
6.5V TO 36V
C1
2 x 2.2µF
EP
fSW = 500kHz
VOUT
5V,3.5A
MAX17633
4.5V to 36V, 3.5A, 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 (MAX17633A & MAX17633B)..........-5.5V to +6.5V
FB to SGND (MAX17633C)..................................-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..............................................................4A
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (Multilayer Board)
(TA = +70°C, derate 30.3mW/°C above +70°C.).....2424.2mW
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
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: 20-Pin 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 1: Junction temperature greater than +125°C degrades operating lifetimes.
Note 2: Package thermal resistances were obtained using the MAX17633 Evaluation Kit with no airflow.
www.maximintegrated.com
Maxim Integrated │ 2
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Electrical Characteristics
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2μF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17633A), VFB = 5.5V (MAX17633B), VFB = 1V (MAX17633C), 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
VEN/UVLO = 0V (Shutdown mode)
2.8
4.5
μA
MODE/SYNC = OPEN, VEXTVCC = 5V
96
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
VIN
Input-Voltage Range
Input-Shutdown Current
VIN
IIN_SH
IQ_PFM
Input-Quiescent Current
4.5
μA
1.8
mA
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 = +25ºC
-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
INTVCC Output-Voltage
Range
INTVCC Current Limit
INTVCC Dropout
INTVCC Undervoltage
Lockout
VINTVCC
IINTVCC_MAX
VINTCC_DO
VINTCC = 4.5V, VIN = 7.5V
30
V
mA
VIN = 4.5V, IINTVCC = 10mA
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
65
125
mΩ
Low-Side nMOS
On-Resistance
RDS_ONL
ILX = 0.3A, sinking
40
80
mΩ
3
μA
LX Leakage Current
www.maximintegrated.com
ILX_LKG
VLX = (VPGND + 1)V to (VIN - 1)V,
TA = +25°C
-2
Maxim Integrated │ 3
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2μF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17633A), VFB = 5.5V (MAX17633B), VFB = 1V (MAX17633C), 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
4.7
5
5.3
μA
MODE/SYNC = SGND or MODE/SYNC =
INTVCC (MAX17633A)
3.256
3.3
3.344
MODE/SYNC = SGND or MODE/SYNC =
INTVCC (MAX17633B)
4.94
5
5.06
MODE/SYNC = SGND or MODE/SYNC =
INTVCC (MAX17633C)
0.888
0.9
0.912
MODE/SYNC = OPEN (MAX17633A)
3.256
3.36
3.44
SS
Charging Current
ISS
FB
FB Regulation Voltage
FB Input-Bias Current
VFB_REG
IFB
MODE/SYNC = OPEN (MAX17633B)
4.94
5.09
5.21
MODE/SYNC = OPEN (MAX17633C)
0.888
0.915
0.938
For MAX17633A
33
For MAX17633B
33
For MAX17633C, 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
VIN_VCC - 0.65
VIN_VCC /2
V
0.75
1.1 × fSW
1.4 × fSW
50
VIH
kHz
ns
2.1
VIL
0.8
V
CURRENT LIMIT
Peak Current-Limit
Threshold
Runaway Current-Limit
Threshold
IPEAK_LIMIT
4.6
5.4
6.2
A
IRUNAWAY_LIMIT
5.35
6.4
7.35
A
PFM Current-Limit
Threshold
IPFM
Valley Current-Limit
Threshold
IVALLEY_LIMIT
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MODE/SYNC = OPEN
MODE/SYNC = OPEN or MODE/SYNC =
INTVCC
MODE/SYNC = GND
1.2
-0.28
0
A
+0.28
A
2.5
Maxim Integrated │ 4
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = unconnected (fSW = 500 kHz), CINTVCC = 2.2μF, VSGND = VPGND = VMODE/SYNC = VEXTVCC = 0V;
VFB = 3.67V (MAX17633A), VFB = 5.5V (MAX17633B), VFB = 1V (MAX17633C), 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
MAX17633A
2.03
2.13
2.22
MAX17633B
3.07
3.22
3.37
MAX17633C
0.55
0.58
0.605
UNITS
RT
Switching Frequency
VFB Hiccup Threshold
fSW
VFB_HICF
VFB_HICF
HICCUP Timeout
(Note 4)
Minimum On-Time
tON(MIN)
Minimum Off-Time
tOFF(MIN)
LX Dead TIme
RESET
RESET Output-Level Low
32768
52
140
LXDT
VRESETL
RESETOutput-Leakage
Current
IRESETLKG
FB Threshold for RESET
Deassertion
FB Threshold for RESET
Assertion
V
Cycles
80
ns
160
ns
5
IRESET = 10mA
kHz
ns
400
mV
100
nA
TA = TJ = 25ºC, VRESET = 5.5V
-100
VFB_OKR
VFB rising
93.8
95
97.8
%
VFB_OKF
VFB falling
90.5
92
94.6
%
RESET Delay after FB
Reaches 95% Regulation
1024
Cycles
165
°C
10
°C
THERMAL SHUTDOWN
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
MAX17633
4.5V to 36V, 3.5A, 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.)
MAX17633A
EFFICIENCY vs. LOAD CURRENT
FIGURE 5 CIRCUIT
toc01
100
80
90
80
85
70
70
VIN = 12V VIN = 24V
60
VIN = 36V
VIN = 4.5V
50
40
80
75
70
20
60
10
55
50
500
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE
MAX17633B
EFFICIENCY vs. LOAD CURRENT
FIGURE 6 CIRCUIT
100
VIN = 24V
VIN = 4.5V
65
0
EFFICIENCY (%)
90
0
10
0
100
1000
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, PFM MODE
100
toc05
70
VIN = 6.5V
50
40
80
70
30
65
20
60
10
55
50
0
500
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, PWM MODE
MAX17633A
LINE AND LOAD REGULATION
FIGURE 5 CIRCUIT
3.310
VIN = 36V
VIN = 6.5V
3.290
3.35
500
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE
www.maximintegrated.com
VIN = 6.5V
40
VIN = 36V
VIN = 12V
3.31
3.29
VIN = 4.5V
0
500
3.310
VIN = 36V
VIN = 24V
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, PFM MODE
50
500
5000
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, DCM MODE
MAX17633A
LINE AND LOAD REGULATION
FIGURE 5 CIRCUIT
toc08
3.33
3.25
0
VIN = 24V
50
0
100
1000
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, PFM MODE
VIN = 12V
3.27
3.285
60
10
10
3.39
OUTPUT VOLTAGE (V)
VIN = 4.5V
3.295
toc06
20
3.37
VIN = 12V
VIN = 24V
500
5000
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, DCM MODE
30
toc07
VIN = 24V
3.300
VIN = 36V
MAX17633A
LINE AND LOAD REGULATION
FIGURE 5 CIRCUIT
3.305
3.280
VIN = 12V
75
VIN = 36V
toc09
VIN = 24V
3.305
OUTPUT VOLTAGE (V)
VIN = 36V
EFFICIENCY (%)
80
85
EFFICIENCY (%)
90
VIN = 24V
50
100
80
60
VIN = 12V
MAX17633B
EFFICIENCY vs. LOAD CURRENT
FIGURE 6 CIRCUIT
90
VIN = 12V
VIN = 36V
VIN = 4.5V
10
95
70
VIN = 24V
40
20
MAX17633B
EFFICIENCY vs. LOAD CURRENT
FIGURE 6 CIRCUIT
toc04
50
30
VIN = 36V
VIN = 12V
toc03
60
90
0
OUTPUT VOLTAGE (V)
toc02
95
30
EFFICIENCY (%)
100
MAX17633A
EFFICIENCY vs. LOAD CURRENT
FIGURE 5 CIRCUIT
90
EFFICIENCY (%)
EFFICIENCY (%)
100
MAX17633A
EFFICIENCY vs. LOAD CURRENT
FIGURE 5 CIRCUIT
3.300
VIN = 12V
3.295
VIN = 4.5V
3.290
3.285
3.280
0
500
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 3.3V OUTPUT, DCM MODE
Maxim Integrated │ 6
MAX17633
4.5V to 36V, 3.5A, 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.)
5.05
toc10
VIN = 24V
5.03
5.02
5.01
5.00
4.99
VIN = 6.5V
4.98
4.97
VIN = 12V
5.10
VIN = 6.5V
5.05
500
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, PWM MODE
4.95
MAX17633B
SOFT-START/SHUTDOWN FROM EN/UVLO
FIGURE 6 CIRCUIT
toc13
VEN/UVLO
VOUT
5V/div
2V/div
0
1000 1500 2000 2500 3000
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, PFM MODE
VEN/UVLO
5V/div
VOUT
2V/div
2A/div
ILX
2A/div
VRESET
5V/div
VRESET
5V/div
2ms/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE, 3.5A LOAD
VEN/UVLO
5V/div
2V/div
ILX
2A/div
VRESET
5V/div
2ms/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE, 35mA LOAD
www.maximintegrated.com
VIN = 6.5V
2A/div
2µs/div
CONDITIONS: 3.5A LOAD CURRENT,
FIXED 3.3V OUTPUT, PWM MODE
1000 1500 2000 2500 3000 3500
LOAD CURRENT (mA)
CONDITIONS: FIXED 5V OUTPUT, DCM MODE
toc15
VEN/UVLO
5V/div
VOUT
2V/div
ILX
2A/div
VRESET
5V/div
2ms/div
CONDITIONS: FIXED 5V OUTPUT, PWM MODE, 35mA LOAD
toc18
20mV/div
ILX
500
MAX17633A
STEADY STATE PERFORMANCE
FIGURE 5 CIRCUIT
20V/div
COUPLED)
0
MAX17633B
SOFT-START WITH PRE-BIAS OF VOLTAGE 2.5V
FIGURE 6 CIRCUIT
toc17
VOUT (AC-
VOUT
VIN = 12V
5.00
MAX17633A
STEADY STATE PERFORMANCE
FIGURE 5 CIRCUIT
VLX
VIN = 24V
5.01
3500
MAX17633A
SOFT-START/SHUTDOWN FROM EN/UVLO
FIGURE 5 CIRCUIT
toc14
MAX17633A
SOFT-START WITH PRE-BIAS OF VOLTAGE 1.65V
FIGURE 5 CIRCUIT
toc16
VIN = 36V
5.02
4.98
500
ILX
1ms/div
CONDITIONS: FIXED 5V OUTPUT, PWM MODE, 3.5A LOAD
5.03
4.99
VIN = 36V
0
toc12
5.04
5.00
4.96
4.95
5.05
VIN = 24V
5.15
VIN = 12V
MAX17633B
LINE AND LOAD REGULATION
FIGURE 6 CIRCUIT
toc11
5.20
VIN = 36V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.04
MAX17633B
LINE AND LOAD REGULATION
FIGURE 6 CIRCUIT
OUTPUT VOLTAGE (V)
MAX17633B
LINE AND LOAD REGULATION
FIGURE 6 CIRCUIT
20V/div
VLX
VOUT (AC-
10mV/div
COUPLED)
0.5A/div
ILX
1µs/div
CONDITIONS: 35mA LOAD CURRENT,
FIXED 3.3V OUTPUT, DCM MODE
Maxim Integrated │ 7
MAX17633
4.5V to 36V, 3.5A, 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.)
MAX17633B
STEADY STATE PERFORMANCE
FIGURE 6 CIRCUIT
MAX17633A
STEADY STATE PERFORMANCE
FIGURE 5 CIRCUIT
toc19
toc20
20V/div
VLX
VOUT (AC-
20mV/div
COUPLED)
ILX
2A/div
VLX
VOUT (AC-
50mV/div
COUPLED)
ILX
1A/div
40µs/div
CONDITIONS: 35mA LOAD CURRENT,
FIXED 3.3V OUTPUT, PFM MODE
MAX17633B
STEADY STATE PERFORMANCE
FIGURE 6 CIRCUIT
MAX17633C
STEADY STATE PERFORMANCE
FIGURE 4 CIRCUIT
toc22
VOUT (AC-
20V/div
VLX
10mV/div
VOUT (AC-
0.2A/div
1µs/div
CONDITIONS: 3.5A LOAD CURRENT,
FIXED 5V OUTPUT, DCM MODE
20mV/div
2A/div
1µs/div
CONDITIONS: 3.5A LOAD CURRENT, 5V OUTPUT, PWM MODE
MAX17633A
LOAD TRANSIENT BETWEEN 0A AND 1.75A
FIGURE 5 CIRCUIT
toc26
toc25
VOUT (AC-
20V/div
VOUT (AC-
VOUT (AC-
100mV/div
COUPLED)
ILX
2A/div
MAX17633C
STEADY STATE PERFORMANCE
FIGURE 4 CIRCUIT
20V/div
ILX
MAX17633C
STEADY STATE PERFORMANCE
FIGURE 4 CIRCUIT
20V/div
100µs/div
CONDITIONS: 35mA LOAD CURRENT,
FIXED 5V OUTPUT, PFM MODE
COUPLED)
VLX
VLX
toc23
COUPLED)
ILX
toc21
20V/div
2µs/div
CONDITIONS: 3.5A LOAD CURRENT,
FIXED 5V OUTPUT, PWM MODE
VLX
MAX17633B
STEADY STATE PERFORMANCE
FIGURE 6 CIRCUIT
100mV/div
COUPLED)
toc24
VLX
20V/div
VOUT (AC-
50mV/div
COUPLED)
ILX
1A/div
40µs/div
CONDITIONS: 35mA LOAD CURRENT, 5V OUTPUT, PFM MODE
MAX17633A
LOAD TRANSIENT BETWEEN 1.75A AND 3.5A
FIGURE 5 CIRCUIT
toc27
VOUT (AC-
100mV/div
COUPLED)
10mV/div
COUPLED)
IOUT
ILX
1A/div
IOUT
2A/div
0.5A/div
1µs/div
100µs/div
CONDITIONS: 35mA LOAD CURRENT, 5V OUTPUT, DCM MODE
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE
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200µs/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE
Maxim Integrated │ 8
MAX17633
4.5V to 36V, 3.5A, 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.)
MAX17633A
LOAD TRANSIENT BETWEEN 0.035A AND 1.75A
FIGURE 5 CIRCUIT
toc28
VOUT (AC-
100mV/div
COUPLED)
IOUT
1A/div
toc29
VOUT (AC100mV/div
COUPLED)
IOUT
400µs/div
CONDITIONS: FIXED 3.3V OUTPUT, PFM MODE
1A/div
toc32
VOUT (AC100mV/div
IOUT
VOUT (AC-
2A/div
100mV/div
COUPLED)
IOUT
1A/div
IOUT
1A/div
MAX17633B
LOAD TRANSIENT BETWEEN 1.75A AND 3.5A
FIGURE 6 CIRCUIT
toc33
VOUT (AC-
100mV/div
COUPLED)
IOUT
2A/div
100µs/div
100µs/div
200µs/div
CONDITIONS: FIXED 5V OUTPUT, PWM MODE
CONDITIONS: 5V OUTPUT, PWM MODE
100mV/div
COUPLED)
200µs/div
CONDITIONS: 5V OUTPUT, PWM MODE
MAX17633B
LOAD TRANSIENT BETWEEN 0A AND 1.75A
FIGURE 6 CIRCUIT
toc31
COUPLED)
toc30
200µs/div
CONDITIONS: FIXED 3.3V OUTPUT, DCM MODE
MAX17633C
LOAD TRANSIENT BETWEEN 1.75A AND 3.5A
FIGURE 4 CIRCUIT
VOUT (AC-
MAX17633C
LOAD TRANSIENT BETWEEN 0A AND 1.75A
FIGURE 4 CIRCUIT
MAX17633A
LOAD TRANSIENT BETWEEN 0.035A AND 1.75A
FIGURE 5 CIRCUIT
CONDITIONS: FIXED 5V OUTPUT, PWM MODE
MAX17633B
LOAD TRANSIENT BETWEEN 0.035A AND 1.75A
FIGURE 6 CIRCUIT
toc34
VOUT (AC-
200mV/div
COUPLED)
IOUT
1A/div
200µs/div
CONDITIONS: FIXED 5V OUTPUT, PFM MODE
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Maxim Integrated │ 9
MAX17633
4.5V to 36V, 3.5A, 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.)
MAX17633B
LOAD TRANSIENT BETWEEN 0.035A AND 1.75A
FIGURE 6 CIRCUIT
MAX17633B
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 6 CIRCUIT
toc36
toc35
VOUT (AC-
100mV/div
COUPLED)
VSYNC
VOUT (AC-
5V/div
20mV/div
COUPLED)
IOUT
VLX
20V/div
ILX
5A/div
1A/div
4µs/div
CONDITIONS: FIXED 5V OUTPUT, PWM MODE,
3.5A LOAD CURRENT, fSW = 550kHz
100µs/div
CONDITIONS: FIXED 5V OUTPUT, DCM MODE
MAX17633B
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 6 CIRCUIT
toc37
VSYNC
VOUT (AC-
MAX17633A
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 5 CIRCUIT
toc38
5V/div
20mV/div
COUPLED)
VSYNC
VOUT (AC-
5V/div
20mV/div
COUPLED)
VLX
20V/div
VLX
20V/div
ILX
5A/div
ILX
5A/div
4µs/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE,
3.5A LOAD CURRENT, fSW = 550kHz
4µs/div
CONDITIONS: FIXED 5V OUTPUT, PWM MODE,
3.5A LOAD CURRENT, fSW = 700kHz
MAX17633B
OVER LOAD PROTECTION
FIGURE 6 CIRCUIT
MAX17633A
EXTERNAL CLOCK SYNCHRONIZATION
FIGURE 5 CIRCUIT
toc39
VSYNC
5V/div
VOUT (AC-
toc40
VOUT
100mV/div
20mV/div
COUPLED)
20V/div
VLX
ILX
ILX
2A/div
5A/div
4µs/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE,
3.5A LOAD CURRENT, fSW = 700kHz
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20ms/div
CONDITIONS: FIXED 5 OUTPUT, PWM MODE
Maxim Integrated │ 10
MAX17633
4.5V to 36V, 3.5A, 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.)
MAX17633A
OVER LOAD PROTECTION
FIGURE 5 CIRCUIT
MAX17633B
CLOSED LOOP BODE PLOT
FIGURE 6 CIRCUIT
toc41
toc42
40
90
30
ILX
80
20
70
10
60
0
50
40
-10
2A/div
30
-20
CROSSOVER
FREQUENCY = 49.1kHz
PHASE MARGIN = 67.2°
-30
20ms/div
CONDITIONS: FIXED 3.3V OUTPUT, PWM MODE
MAX17633C
CLOSED LOOP BODE PLOT
FIGURE 4 CIRCUIT
40
0
50
40
30
CROSSOVER
FREQUENCY = 47.8kHz
PHASE MARGIN = 69.1°
-30
1k
10k
FREQUENCY (Hz)
GAIN (dB)
60
PHASE (˚)
70
10
-40
40
80
-20
10
1k
MAX17633A
CLOSED LOOP BODE PLOT
FIGURE 5 CIRCUIT
100
20
-10
20
0
10k
100k
FREQUENCY (Hz)
CONDITIONS: 5V FIXED OUTPUT, 3.5A LOAD CURRENT, PWM MODE
90
30
GAIN (dB)
toc43
-40
PHASE (˚)
GAIN (dB)
100mV/div
90
20
80
10
70
0
60
-10
-20
10
-30
CONDITIONS: 5V ADJUSTABLE OUTPUT, 3.5A LOAD CURRENT, PWM MODE
100
30
20
0
100k
toc44
-40
PHASE (°)
VOUT
100
50
CROSSOVER
FREQUENCY = 56.4kHz
PHASE MARGIN = 61.9°
1k
10k
FREQUENCY (Hz)
40
30
100k
CONDITIONS: 3.3V FIXED OUTPUT, 3.5A LOAD CURRENT, PWM MODE
TUV Rheinland
Final_ScanV
MaximIC_MAX17633
Final_ScanH
MAX17633C, 5V OUTPUT, 3.5A LOAD CURRENT
RE 30MHz-1GHz
Limit
RADIATED EMI CURVE
toc46
70
70.0
50.0
50
AMPLITUDE (dBµV)
Am p litu d e (d Bu V /m )
60.0
60
40.0
40
30.0
30
20.0
20
CISPR-22 CLASS B QP LIMIT
VERTICAL
SCAN
10.0
10
00
-10.0
-10
30.0M
30
100.0M
100
HORIZONTAL
SCAN
1.0G
1000
Frequency (Hz) (MHz)
FREQUENCY
RE 30MHz-1GHz_0-360deg_90deg
step_1-4mtr Height_Quick
CONDITION: MEASURED
ON THE Scan_Test7.TIL
MAX17633CEVKIT#
03:22:51 PM, Wednesday, November 28, 2018
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Maxim Integrated │ 11
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Pin Configuration
PGND
1
IN
2
IN
3
EN/UVLO
RESET
BST
LX
LX
LX
NC
20
19
18
17
16
+
15
PGND
14
IN
13
NC
4
12
EXTVCC
5
11
MODE/SYNC
*EP
MAX17633A
MAX17633B
MAX17633C
6
7
8
9
10
INTVCC
SGND
SS
FB
RT
20-PIN TQFN (4mm × 4mm)
*EXPOSED PAD
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Maxim Integrated │ 12
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Pin Description
PIN
NAME
FUNCTION
Power Ground Pin of the Converter. Connect externally to the power ground plane. Refer to the
MAX17633 EV kit datasheet for a layout example
1, 15
PGND
2, 3,14
IN
4
EN/UVLO
5
RESET
Open-Drain RESET Output. The RESET output 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
Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time.
9
FB
Feedback Input. Connect the output-voltage node (VOUT) to FB for MAX17633A and MAX17633B.
Connect FB to the center node of an external resistor-divider from the output to SGND to set the output
voltage for MAX17633C. 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) section for more details.
11
MODE/
SYNC
12
EXTVCC
Power-Supply Input Pin. 4.5V to 36V input-supply range. Decouple to PGND with a minimum of 2.2μF
capacitor; place the capacitor close to the IN and PGND pins.
Enable/Undervoltage Lockout Pin. Drive EN/UVLO high 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
the IN pin for always on operation. Pull low for disabling the device.
Analog Ground
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.
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.
13, 16
NC
Not Connected
17–19
LX
Switching Node Pins. Connect LX pins to the switching side of the inductor.
20
BST
—
EP
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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 MAX17633 EV kit data sheet for an
example of the correct method for EP connection and thermal vias.
Maxim Integrated │ 13
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Functional Diagram
MAX17633A/MAX17633B/MAX17633C
EXTVCC
BST
INTVCC
LDO
SGND
IN
CURRENTSENSE
LOGIC
EN/UVLO
ENOK
1.215V
HICCUP
LX
PWM/PFM/HICCUP
LOGIC
RT
OSCILLATOR
PGND
*S1
FB
*S2
*S3
R1
ERROR AMPLIFIER /
LOOP COMPENSATION
THERMAL
SHUTDOWN
R2
SLOPE
COMPENSATION
INTVCC
SWITCH-OVER LOGIC
MODE
SELECTION
LOGIC
SS
HICCUP
*S1 – CLOSE, *S2,*S3 – OPEN FOR MAX17633C
*S1 – OPEN, *S2,*S3 – CLOSE FOR MAX17633A/MAX17633B
R1 – 132.7kΩ, R2 – 29.1kΩ FOR MAX17633B
R1 – 77.7kΩ, R2 – 29.1kΩ FOR MAX17633A
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ENOK
FB
MODE/SYNC
RESET
RESET
LOGIC
Maxim Integrated │ 14
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Detailed Description
The MAX17633 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 3.5A current. The MAX17633
is available in three variants MAX17633A, MAX17633B,
and MAX17633C. The MAX17633A and MAX17633B are
the fixed 3.3V and fixed 5V output voltage parts, respectively. MAX17633C 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 feedback (FB) voltage regulation
accuracy over -40ºC to +125ºC is ±1.3% for MAX17633A,
MAX17633B, and MAX17633C.
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
high-side 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 features adjustable-input undervoltage lockout, adjustable soft-start, open drain RESET, and
external clock synchronization features. The MAX17633
offers a low minimum on-time that enables designing the
converter at higher switching frequencies, which helps
reduce the solution size.
Mode Selection and External Clock Synchronization (MODE/SYNC)
The MAX17633 supports 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 VCC 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
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loads. If the state of the MODE/SYNC pin is high (> VM_
DCM), the device operates in DCM mode at light loads.
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 in the Electrical
Characteristics table for details.
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 (1.2A 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 reduce 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 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 │ 15
MAX17633
4.5V to 36V, 3.5A, 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.
Table 1. Switching Frequency vs.
RRT Resistor
SWITCHING FREQUENCY
(KHZ)
Linear Regulator (INTVCC and EXTVCC)
The MAX17633 has an internal low dropout (LDO) 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 EXTVCC is greater than 4.7V (typ),
then the internal LDO is disabled and INTVCC is powered from EXTVCC. Powering INTVCC (INTVCC output
voltage is 5V typ) from EXTVCC increases efficiency at
higher input voltages. 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 MAX17633 employs an undervoltage lockout circuit
that forces the converter off when INTVCC falls below
VINTVCC_UVF (3.8V typ). The buck converter can be
immediately enabled again when INTVCC > VINTVCC_
UVR (4.2typ). The 400mV UVLO hysteresis prevents chattering on power-up and power-down.
In applications where the buck converter output is connected to the 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
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RRT RESISTOR
(KΩ)
400
50.8
500
OPEN
500
40.2
2200
8.06
Where RRT is in kΩ and fSW is in kHz. Leaving the RT pin
open forces the device to operate at a 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:
VIN(MIN) =
(
(
VOUT + I OUT(MAX) × R DCR(MAX) + R DS_ONL(MAX)
(
1 - f SW(MAX) × t OFF_MIN(MAX)
)
(
))
)
+ IOUT(MAX) × (RDS_ONH(MAX) − RDS_ONL(MAX))
VOUT
VIN(MAX) = f
SW(MAX) × tON_MIN(MAX)
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
on-state resistance of low-side and high-side internal
MOSFETs respectively.
Maxim Integrated │ 16
MAX17633
4.5V to 36V, 3.5A, 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 (5.4A typ). A runaway current limit on the
high-side switch current at IRUNAWAY_LIMIT (6.4A typ)
protects the device under high input voltage, output shortcircuit conditions when there is insufficient output voltage
available to restore the inductor current that has built up
during the on period of the step-down converter. One
occurrence of the runaway current limit triggers hiccup
mode. In addition, if feedback voltage drops to VFB_HICF
(0.58V typ) due to a fault condition, hiccup mode is triggered 1024 clock cycles after soft-start 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 VFB_OKR and
95% of VFB_REG. RESET goes low when the regulator output voltage drops to below VFB_OKF and 92% of
VFB_REG. RESET also goes low during thermal shutdown
or when the 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.
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Thermal-Shutdown Protection
Thermal-shutdown protection limits junction temperature
in the device. When the junction temperature of the device
exceeds +165ºC, 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 controller,
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 │ 17
MAX17633
4.5V to 36V, 3.5A, 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:
1.5
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
(5.4A 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
t RESPONSE ≅
0.35
fC
where:
ISTEP = Load current step,
tRESPONSE = Response time of the controller,
ΔVOUT = Allowable output-voltage deviation,
fC = Target closed-loop crossover frequency.
Select fC to be 1/10th of fSW for the switching frequencies
less than or equal to 800kHz. If the switching frequency is
more than 800kHz, select fC to be 80kHz. Actual derating
of ceramic capacitors with DC-voltage must be consid-
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ered while selecting the output capacitor. Derating curves
are available from all major ceramic capacitor vendors
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 start-up, device operates at half the
programmed switching frequency until the output voltage
reaches 66.7% of set output nominal voltage.
Setting the Input Undervoltage-Lockout Level
The device offers an adjustable input undervoltage-lockout
level. Set the voltage at which the device turns on with
a resistive voltage-divider connected from INto SGND.
Connect the center node of the divider to the EN/UVLO pin.
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) or 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 the signal source and the EN/UVLO pin to reduce
voltage ringing on the line.
Maxim Integrated │ 18
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
VOUT
VIN
MAX17633A
MAX17633B
MAX17633C
MAX17633C
RU
RTOP
EN/UVLO
FB
RB
RBOTTOM
Figure 1. Setting the Input Undervoltage Lockout
Figure 2. Setting the Output Voltage
Adjusting Output Voltage
where:
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 MAX17633C. Connect the outputvoltage node (VOUT) to the FB pin for MAX17633A and
MAX17633B. Use the following procedure to choose the
resistive voltage-divider values:
Calculate resistor RU from the output to the FB pin as
follows:
270
RU = f × C
C
OUT
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 a temperature rise of the part are estimated as follows:
(
( 1 )) (
PLOSS = POUT × η − 1 − IOUT2 × RDCR
η = Efficiency of the converter
RDCR = DC resistance of the inductor.
See Typical Operating Characteristics for more information on efficiency at typical operating conditions.
For a typical multilayer board, the thermal performance
metrics for the package are given below:
θJA = 26ºC/W
θJC = 2ºC/W
where RU is in kΩ, crossover frequency fC is in Hz, and
the output capacitor COUT is in F. Calculate resistor RB
connected from the FB pin to SGND as follows:
RB =
POUT = Output power
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
degrade operating lifetimes.
)
POUT = VOUT × IOUT
www.maximintegrated.com
Maxim Integrated │ 19
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
PCB Layout Guidelines
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
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 INTVCCpin
also should be placed close to the pin to reduce effects of
trace impedance.
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.
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.
For a sample layout that ensures first pass success, refer
to the MAX17633 evaluation kit layout available at www.
maximintegrated.com.
Typical Application Circuits
Typical Application Circuit —Adjustable 3.3V Output
EN/UVLO
IN
RT
IN
C1
2.2μF
2x
IN
BST
MODE/SYNC
INTVCC
C3
2.2μF
LX
MAX17633C
LX
LX
SGND
RESET
SS
VIN
4.5V TO 36V
C5
0.1μF
L1
5.6μH
VOUT 3.3V, 3.5A
C4
47μF
2x
R1
76.8kΩ
FB
PGND
PGND
EXTVCC
C2
5600pF
fSW = 500kHz
L1: XAL5050-562ME
C1: GRM32ER72A225KA35
C4: GRM32ER70J476KE20
R2
28.7kΩ
MODE/SYNC:
1. CONNECT TO SGND FOR PWM MODE
2. CONNECT TO INTVCC FOR DCM MODE
3. LEAVE OPEN FOR PFM MODE
Figure 3. Adjustable 3.3V Output with 500kHz Switching Frequency
www.maximintegrated.com
Maxim Integrated │ 20
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Typical Application Circuits (continued)
Typical Application Circuit—Adjustable 5V Output
EN/UVLO
IN
C1
2.2μF
2x
IN
IN
RT
BST
C5
0.1μF
MODE/SYNC
LX
INTVCC
C3
2.2μF
VIN
6.5V TO 36V
MAX17633C
LX
RESET
VOUT 5V, 3.5A
C4
22μF
2x
LX
SGND
R1
133kΩ
FB
PGND
SS
L1
6.8μH
EXTVCC
PGND
C2
5600pF
VOUT
fSW = 500kHz
L1: XAL5050-682ME
C1: GRM32ER72A225KA35
C4: GRM32ER71A226K
R2
28.7kΩ
MODE/SYNC:
1. CONNECT TO SGND FOR PWM MODE
2. CONNECT TO INTVCC FOR DCM MODE
3. LEAVE OPEN FOR PFM MODE
Figure 4. Adjustable 5V Output with 500kHz Switching Frequency
Typical Application Circuit —Fixed 3.3V Output
EN/UVLO
IN
IN
C1
2.2μF
2x
IN
RT
BST
MODE/SYNC
INTVCC
C3
2.2μF
LX
MAX17633A
LX
LX
SGND
RESET
SS
VIN
4.5V TO 36V
C5
0.1μF
L1
5.6μH
VOUT 3.3V, 3.5A
C4
47μF
2x
FB
PGND
PGND
EXTVCC
C2
5600pF
fSW = 500kHz
L1: XAL5050-562ME
C1: GRM32ER72A225KA35
C4: GRM32ER70J476KE20
MODE/SYNC:
1. CONNECT TO SGND FOR PWM MODE
2. CONNECT TO INTVCC FOR DCM MODE
3. LEAVE OPEN FOR PFM MODE
Figure 5. Fixed 3.3V Output with 500kHz Switching Frequency
www.maximintegrated.com
Maxim Integrated │ 21
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Typical Application Circuits (continued)
Typical Application Circuit —Fixed 5V Output
IN
EN/UVLO
C1
2.2μF
2x
IN
IN
RT
BST
MODE/SYNC
INTVCC
C3
2.2μF
LX
MAX17633B
LX
C5
0.1μF
L1
6.8μH
RESET
VOUT 5V, 3.5A
C4
22μF
2x
LX
SGND
SS
VIN
6.5V TO 36V
FB
PGND
PGND
EXTVCC
fSW = 500kHz
L1: XAL5050-682ME
C1: GRM32ER72A225KA35
C4: GRM32ER71A226K
C2
5600pF
MODE/SYNC:
1. CONNECT TO SGND FOR PWM MODE
2. CONNECT TO INTVCC FOR DCM MODE
3. LEAVE OPEN FOR PFM MODE
Figure 6. Fixed 5V Output with 500kHz Switching Frequency
Ordering Information
OUTPUT
VOLTAGE
(V)
PIN-PACKAGE
MAX17633AATP+
3.3
20 TQFN-EP*
(4mm x 4mm)
MAX17633AATP+T
3.3
20 TQFN-EP*
(4mm x 4mm)
MAX17633BATP+
5
20 TQFN-EP*
(4mm x 4mm)
MAX17633BATP+T
5
20 TQFN-EP*
(4mm x 4mm)
MAX17633CATP+
Adjustable
20 TQFN-EP*
(4mm x 4mm)
MAX17633CATP+T
Adjustable
20 TQFN-EP*
(4mm x 4mm)
PART NUMBER
+Denotes a lead(Pb)-free/RoHS compliant package
*EP = Exposed pad.
T = Tape and reel.
www.maximintegrated.com
Maxim Integrated │ 22
MAX17633
4.5V to 36V, 3.5A, High Efficiency,
Synchronous Step-Down, DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
0
4/18
Initial release
2/19
Updated the General Description, Benefits and Features, Electrical Characteristics,
Pin Description, Detailed Description, and Operating Input-Voltage Range sections,
and TOC01–TOC12; replaced the Typical Application Circuit and Mode Selection and
External Clock Synchronization (MODE/SYNC); added TOC45–TOC46
4–5, 7–11,
14, 16, 18, 19
7/20
Updated the General Description, Benefits and Features, Electrical Characteristics,
Pin Configuration, Pin Description, Detailed Description, PFM Mode Operation,
Overcurrent Protection/Hiccup Mode, Output Capacitor Selection, Thermal-Shutdown
Protection, Power Dissipation, and added the MAX17633AATP+T, MAX17633BATP+T
and MAX17633CATP+T to the Ordering Information section; updated TOC34,
TOC36–TOC39, TOC45, TOC46 and replaced the Typical Application Circuit
1–3, 5, 9–13,
15–19, 22
1
2
PAGES
CHANGED
DESCRIPTION
—
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. │ 23
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