Maxim MAX17572 4.5vâ 60v, 1a, high-efficiency, synchronous Datasheet

EVALUATION KIT AVAILABLE
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensation
General Description
The MAX17572 high-efficiency, high-voltage, synchronous
step-down DC-DC converter with integrated MOSFETs
operates over a 4.5V to 60V input. The converter can
deliver up to 1A and generates output voltages from 0.9V
up to 0.9 x VIN. The feedback (FB) voltage is accurate to
within ±1.2% over -40°C to +125°C. The MAX17572 uses
peak current-mode control.
The device is available in a 12-pin (3mm x 3mm) TDFN
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 for Any Output Voltage
• All-Ceramic Capacitors, Compact Layout
●● Reduces Number of DC-DC Regulators to Stock
• Wide 4.5V to 60V Input
• Adjustable 0.9V to 0.9 x VIN Output
• Continuous 1A Current Over Temperature
• 400kHz to 2.2MHz Adjustable Switching Frequency
with External Synchronization
●● Reduces Power Dissipation
• Peak Efficiency > 92%
• Auxiliary Bootstrap LDO for Improved Efficiency
• 4.65µA Shutdown Current
●● Operates Reliably in Adverse Industrial Environments
• Hiccup Mode Overload Protection
• Adjustable Soft-Start
• Built-In Output-Voltage Monitoring with RESET
• Programmable EN/UVLO Threshold
• Monotonic Startup into Prebiased Load
• 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.
19-8640; Rev 0; 9/16
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Absolute Maximum Ratings
VCC to PGND........................................................-0.3V to +6.5V
LX Total RMS Current.........................................................±1.6A
Continuous Power Dissipation (TA = +70°C)
(derate 24.4mW/°C above +70°C) (Multilayer board)...1951mW
Output Short-Circuit Duration.....................................Continuous
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65°C to +160°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................ +260°C
VIN to PGND..........................................................-0.3V to +65V
EN/UVLO to GND..................................................-0.3V to +65V
EXTVCC to GND....................................................-0.3V to +26V
BST to PGND.........................................................-0.3V to +70V
LX to PGND................................................-0.3V to (VIN + 0.3)V
BST to LX..............................................................-0.3V to +6.5V
BST to VCC............................................................-0.3V to +65V
RESET, SS, RT/SYNC to GND.............................-0.3V to +6.5V
PGND to GND.......................................................-0.3V to +0.3V
FB to GND.............................................................-0.3V to +1.5V
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. Junction temperature greater than +125°C degrades operating lifetimes.
Package Thermal Characteristics (Note 1)
Junction-to-Ambient Thermal Resistance (θJA)...............41°C/W
Junction-to-Case Thermal Resistance (θJC)...................8.5°C/W
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
(VIN = VEN/UVLO = 24V, RRT = 40.2k, CVCC = 2.2µF, VPGND = VGND = EXTVCC = 0, LX = SS = RESET = OPEN, VBST to VLX = 5V,
VFB = 1V, TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
60
V
7.25
µA
INPUT SUPPLY (VIN)
Input Voltage Range
Input Shutdown Current
Input Quiescent Current
V­IN_
IIN-SH
IQ_PWM
4.5
VEN/UVLO = 0V (shutdown mode)
4.65
Normal switching mode, FSW = 500kHz,
VFB = 0.8V, EXTVCC = GND
5.2
mA
ENABLE/UVLO (EN)
EN/UVLO Threshold
EN/UVLO Input Leakage
Current
VENR
VEN/UVLO rising
1.19
1.215
1.26
V
VENF
VEN/UVLO falling
1.068
1.09
1.131
V
+50
nA
IENLKG
VEN/UVLO = 1.25V, TA = 25°C
-50
1mA ≤ IVCC ≤ 15mA
4.75
5
5.25
V
6V ≤ VIN ≤ 60V; IVCC = 1mA
4.75
5
5.25
V
25
54
100
mA
VCC LDO
VCC Output Voltage Range
VCC Current Limit
VCC Dropout
VCC UVLO
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VCC
IVCC-MAX
VCC = 4.3V, VIN = 6.5V
VCC-DO
VIN = 4.5V , IVCC = 15mA
4.15
VCC-UVR
Rising
4.05
4.2
4.3
V
V
VCC-UVF
Falling
3.65
3.8
3.9
V
Maxim Integrated │ 2
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = 40.2k, CVCC = 2.2µF, VPGND = VGND = EXTVCC = 0, LX = SS = RESET = OPEN, VBST to VLX = 5V,
VFB = 1V, TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
EXTVCC rising
4.56
4.7
4.84
V
EXTVCC falling
4.3
4.45
4.6
V
0.3
V
26.5
60
100
mA
EXT LDO
EXTVCC Switchover Voltage
EXTVCC Dropout
EXTVCC-DO
EXTVCC = 4.75V , IEXTVCC = 15mA
EXTVCC Current Limit
EXT VCCILIM
VCC = 4.5V, EXTVCC = 7V
HIGH-SIDE MOSFET AND LOW-SIDE MOSFET DRIVER
High-Side nMOS On-Resistance
RDS-ONH
ILX = 0.3A
330
620
mΩ
Low-Side nMOS On-Resistance
RDS-ONL
ILX = 0.3A
170
320
mΩ
+2
µA
LX Leakage Current
(LX to PGND_)
ILXLKG
VLX = VIN-1V; VLX = VPGND +1V; TA =
25°C
-2
VSS = 0.5 V
4.7
5
5.3
µA
0.889
0.9
0.911
V
+50
nA
SOFT START
Soft-Start Current
ISS
FEEDBACK (FB)
FB Regulation Voltage
VFB_REG
FB Input Bias Current
IFB
0 ≤ VFB ≤ 1V, TA = 25°C
-50
CURRENT LIMIT
Peak Current-Limit Threshold
IPEAK-LIMIT
1.5
1.75
2.00
A
Runaway Current-Limit
Threshold
IRUNAWAY-
1.75
2
2.25
A
LIMIT
Negative Current-Limit Threshold
0.65
A
RT/SYNC AND TIMINGS
Switching Frequency
VFB Undervoltage Trip Level to
Cause HICCUP
FSW
VFB-HICF
RRT = OPEN
430
490
550
kHz
RRT = 51.1kΩ
370
400
430
kHz
RRT = 40.2kΩ
475
500
525
kHz
RRT = 8.06kΩ
1950
2200
2450
kHz
0.56
0.58
0.65
V
HICCUP Timeout
32768
Minimum On-Time
tON_MIN
Minimum Off-Time
tOFF_MIN
LX Dead Time
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140
Cycles
60
80
ns
150
160
ns
5
ns
Maxim Integrated │ 3
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Electrical Characteristics (continued)
(VIN = VEN/UVLO = 24V, RRT = 40.2k, CVCC = 2.2µF, VPGND = VGND = EXTVCC = 0, LX = SS = RESET = OPEN, VBST to VLX = 5V,
VFB = 1V, TA = -40°C to 125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 2)
PARAMETER
SYMBOL
SYNC Frequency Capture
Range
CONDITIONS
FSW set by RRT
SYNC Pulse Width
SYNC Threshold
RESET
VIH
MIN
TYP
1.1 x
FSW
MAX
UNITS
1.4 x
FSW
50
ns
2.1
V
VIL
RESET Output Level Low
IRESET = 10mA
RESET Output Leakage Current
TA = TJ = 25°C, VRESET = 5.5V
-100
0.8
V
400
mV
+100
nA
VOUT Threshold for RESET
Assertion
VOUT-OKF
VFB falling
90.5
92
94.6
%
VOUT Threshold for RESET
De-Assertion
VOUT-OKR
VFB rising
93.8
95
97.8
%
RESET Delay After FB Reaches
95% Regulation
1024
Cycles
165
°C
10
°C
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
TSHDNR
Thermal-Shutdown Hysteresis
TSHDNHY
Temp rising
Note 2: All limits are 100% tested at TA = +25°C. Limits over the operating temperature range and relevant supply voltage range
are guaranteed by design and characterization
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Maxim Integrated │ 4
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Typical Operating Characteristics
(VIN = VEN/UVLO = 24V, VGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 2.2μF, CBST = 2.2μF, CSS = 5600pF, TA = -40°C to +125°C,
unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless otherwise noted.)
MAX17572, 5V OUTPUT, PWM MODE,
EFFICIENCY VS. LOAD CURRENT
FIGURE 4 CIRCUIT
toc01
100
100
90
90
80
70
VIN = 24V
60
VIN = 36V
VIN = 48V
EFFICIENCY (%)
EFFICIENCY (%)
80
VIN = 12V
50
70
VIN = 36V
60
VIN = 24V
50
30
0
200
400
600
800
20
1000
0
0
MAX17572, 5V OUTPUT, PWM MODE,
LOAD AND LINE REGULATION
FIGURE 4 CIRCUIT
5.04
toc03
1
1
1
MAX17572, 3.3V OUTPUT, PWM MODE,
LOAD AND LINE REGULATION
FIGURE 5 CIRCUIT
toc04
3.50
3.45
5.03
VIN=24V
VIN=48V
VIN=24V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0
LOAD CURRENT (mA)
LOAD CURRENT (mA)
5.02
5.01
VIN=12V
VIN=36V
5.00
4.99
VIN = 48V
VIN = 12V
40
40
30
MAX17572,3.3V OUTPUT, PWM MODE,
EFFICIENCY VS. LOAD CURRENT
FIGURE 5 CIRCUIT
toc02
0
200
400
600
800
1000
3.35
VEN/UVLO
5V/div
VOUT
2V/div
IOUT
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VIN=36V
3.25
3.20
0.00
0.20
0.40
0.60
0.80
1.00
LOAD CURRENT (mA)
MAX17572, SOFT-START/SHUTDOWN FROM EN/UVLO,
5V OUTPUT, 1A LOAD CURRENT,
toc05
FIGURE 4 CIRCUIT)
1ms/div
VIN=12V
3.30
LOAD CURRENT (mA)
VRESET
VIN=48V
3.40
MAX17572, SOFT-START/SHUTDOWN FROM EN/UVLO,
3.3V OUTPUT, 1A LOAD CURRENT,
toc06
FIGURE 5 CIRCUIT)
VEN/UVLO
5V/div
VOUT
2V/div
0.5A/div
IOUT
0.5A/div
5V/div
VRESET
5V/div
1mS/div
Maxim Integrated │ 5
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 2.2μF, CBST = 2.2μF, CSS = 5600pF, TA = -40°C to +125°C,
unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless otherwise noted.)
MAX17572, SOFT-START WITH 2.5V PREBIAS,
5V OUTPUT, PWM MODE,
FIGURE 4 CIRCUIT
MAX17572, SOFT-START WITH 2.5V PREBIAS,
3.3V OUTPUT, PWM MODE,
toc08
FIGURE 5 CIRCUIT
toc07
5V/div
5V/div
VEN/UVLO
1V/div
VEN/UVLO
1V/div
VOUT
VOUT
VRESET
5V/div
1mS/div
1mS/div
MAX17572, STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, 1A LOAD CURRENT,
FIGURE 4 CIRCUIT
toc09
VOUT
(AC)
5V/div
VRESET
50mV/div
MAX17572, STEADY-STATE SWITCHING WAVEFORMS,
5V OUTPUT, NO LOAD CURRENT,
toc10
FIGURE 4 CIRCUIT
VOUT
(AC)
50mV/div
VLX
10V/div
VLX
10V/div
ILX
1A/div
ILX
500mA/div
2µs/div
2µS/div
MAX17572, 5V OUTPUT, PWM MODE, FIGURE 4
CIRCUIT (LOAD CURRENT STEPPED
toc11
FROM 0.5A TO 1A
MAX17572, 3.3V OUTPUT, PWM MODE, FIGURE 5
CIRCUIT (LOAD CURRENT STEPPED
toc12
FROM 0.5A TO 1A)
VOUT
AC
100mV/div
VOUT
AC
50mV/div
ILOAD
500mA/div
ILOAD
500mA/div
100μS/div
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100μS/div
Maxim Integrated │ 6
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Typical Operating Characteristics (continued)
(VIN = VEN/UVLO = 24V, VGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 2.2μF, CBST = 2.2μF, CSS = 5600pF, TA = -40°C to +125°C,
unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless otherwise noted.)
MAX17572, 5V OUTPUT, PWM MODE, FIGURE 4
CIRCUIT (LOAD CURRENT STEPPED
toc13
FROM NO LOAD TO 0.5A)
MAX17572, 3.3V OUTPUT, PWM MODE, FIGURE 5
CIRCUIT (LOAD CURRENT STEPPED
toc14
FROM NO LOAD TO 0.5A)
VOUT
AC
100mV/div
VOUT
AC
ILOAD
500mA/div
ILOAD
100μS/div
50mV/div
500mA/div
100μS/div
MAX17572,APPLICATION OF EXTERNAL CLOCK
AT 600kHz, 5V OUTPUT, FIGURE 1 CIRCUIT
MAX17572, OVERLOAD PROTECTION
5V OUTPUT, FIGURE 4 CIRCUIT toc15
VOUT
toc16
20mV/div
ILX
0.5A/div
VLX
10V/div
VSYNC
2V/div
4μs/div
20ms/div
MAX17572, 5V OUTPUT, 1A LOAD CURRENT,
BODE PLOT, FIGURE 4 CIRCUIT
toc17
MAX17572, 3.3V OUTPUT, 1A LOAD CURRENT,
BODE PLOT, FIGURE 5 CIRCUIT
toc18
GAIN
CROSSOVER FREQUENCY
= 47.9KHz,
PHASE MARGIN = 70.5°
FREQUENCY (Hz)
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PHASE
GAIN
GAIN (dB)
GAIN (dB)
PHASE
CROSSOVER FREQUENCY =
42.9kHz,
PHASE MARGIN = 64.5°
FREQUENCY (Hz)
Maxim Integrated │ 7
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Pin Configuration
TOP VIEW
VIN
1
EN/UVLO
MAX17572
12
PGND
2
11
LX
RESET
3
10
BST
SS
4
9
EXTV CC
VCC
5
8
GND
RT/SYNC
6
7
FB
+
EP*
TDFN
(3mm x 3mm)
*EP = EXPOSED PAD , CONNECTED TO GND
Pin Description
PIN
NAME
FUNCTION
VIN
1
Power-Supply Input. The input supply range is from 4.5V to 60V.
EN/UVLO
2
Enable/Undervoltage Lockout Input. Drive EN/UVLO high to enable the output voltage. Connect to the
centre of the resistive divider between VIN and GND to set the input voltage (undervoltage threshold) at
which the device turns on. Pull up to VIN for always on.
RESET
3
Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set value. RESET
goes high 1024 clock cycles after FB rises above 95% of its set value. RESET is valid when the device is
enabled and VIN is above 4.5V.
SS
4
Soft-Start Input. Connect a capacitor from SS to GND to set the soft-start time.
VCC
5
5V LDO Output. Bypass VCC with 2.2μF ceramic capacitance to PGND.
RT/SYNC
6
Oscillator Timing Resistor Input. Connect a resistor from RT/SYNC to GND to program the switching
frequency from 400kHz to 2.2MHz. See the Switching Frequency (RT/SYNC) section for details. An external
pulse can be applied to RT/SYNC through a coupling capacitor to synchronize the internal clock to the
external pulse frequency. See the External Synchronization section for details.
FB
7
Feedback Input. Connect FB to the center of the resistive divider between output voltage and GND.
GND
8
Analog Ground.
EXTVCC
9
External Power-Supply Input for the Internal LDO. Applying a voltage between 4.84V and 24V at the
EXTVCC pin will bypass the internal LDO and improve efficiency.
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Maxim Integrated │ 8
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Pin Description (continued)
PIN
NAME
FUNCTION
BST
10
Boost Flying Capacitor. Connect a 0.1μF ceramic capacitor between BST and LX.
LX
11
Switching Node. Connect LX to the switching side of the inductor. LX is high impedance when the device is
in shutdown mode.
PGND
12
Power Ground. Connect PGND externally to the power ground plane. Connect GND and PGND pins
together at the ground return path of the VCC bypass capacitor.
EP
—
Exposed Pad. Connect to the GND pin of the IC. Connect to a large copper plane below the IC to improve
heat dissipation capability.
Functional (or Block) Diagram
VIN
MAX17572
EXTVCC
VCC
INTERNAL LDO
REGULATOR
POK
BST
VCC_INT
EN/UVLO
PEAK-LIMIT
CHIPEN
1.215V
THERMAL
SHUTDOWN
DH
CLK
OSCILLATOR
CURRENT
SENSE
AMPLIFIER
HIGH SIDE
DRIVER
LX
PWM
CONTROL LOGIC
RT/SYNC
CS
CURRENT
SENSE LOGIC
LOW SIDE
DRIVER
DL
PGND
SLOPE
CS
FB
SS
EXTERNAL
SOFT START
CONTROL
ERROR
AMPLIFIER
PWM
SINK LIMIT
COMP
0.76V
CLK
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ZX/ILIMIN
FB
NEGATIVE
CURRENT
REF
2ms
DELAY
RESET
GND
Maxim Integrated │ 9
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Detailed Description
The MAX17572 high-efficiency, high-voltage, synchronous
step-down DC-DC converter with integrated MOSFETs
operates over a 4.5V to 60V input. The converter can
deliver up to 1A and generates output voltages from 0.9V
up to 0.9 x VIN. The feedback (FB) voltage is accurate to
within ±1.2% over -40°C to +125°C.
The device features a peak-current-mode control architecture.
An internal transconductance error amplifier produces an
integrated error voltage at an internal node that sets the
duty cycle using a PWM comparator, a high-side currentsense 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 RT/SYNC pin to program the
switching frequency and to synchronize to an external
clock. The device integrates adjustable-input, undervoltagelockout, adjustable soft-start, open-drain RESET and
auxiliary bootstrap LDO.
Linear Regulator (VCC)
The device has two internal (low-dropout) regulators
(LDOs) which powers VCC. One LDO is powered from
VIN and the other LDO is powered from EXTVCC
(EXTVCC LDO). Only one of the two LDOs is in operation
at a time, depending on the voltage levels present at
EXTVCC. If EXTVCC voltage is greater than 4.7V (typ),
VCC is powered from EXTVCC. If EXTVCC is lower than
4.7V (typ), VCC is powered from VIN. Powering VCC from
EXTVCC increases efficiency at higher input voltages.
EXTVCC voltage should not exceed 24V.
Typical VCC output voltage is 5V. Bypass VCC to PGND
with a 2.2μF low-ESR ceramic capacitor. VCC powers
the internal blocks and the low-side MOSFET driver and
recharges the external bootstrap capacitor. Both LDO
can source up to 60mA (typ). The MAX17572 employs an
undervoltage-lockout circuit that forces both the regulators
off when VCC falls below 3.8V (typ). The regulators can
be immediately enabled again when VCC is higher than
4.2V. The 400mV UVLO hysteresis prevents chattering on
power-up/power-down.
In applications where the buck converter output is connected
to the EXTVCC pin, if the output is shorted to ground, then
transfer from EXTVCC LDO to the internal LDO happens
seamlessly without any impact on the normal functionality.
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Switching Frequency Selection and External
Frequency synchronization
The switching frequency of the MAX17572 can be
programmed from 400kHz to 2.2MHz by using a resistor
connected from the RT/SYNC pin to GND. When no
resistor is used, the frequency is programmed to 490kHz.
The switching frequency (FSW) is related to the resistor
connected at the RT pin (RRT) by the following equation:
=
R RT
21× 10 3
− 1.7
FSW
where RRT is in kΩ and FSW is in kHz. See Table 1 for RT
resistor values for a few common switching frequencies.
The RT/SYNC pin can be used to synchronize the
device’s internal oscillator to an external system clock.
A resistor must be connected from the RT/SYNC pin
to GND to be able to synchronize the MAX17572 to an
external clock. The external clock should be coupled to
the RT/SYNC pin through a network, as shown in Figure
1. When an external clock is applied to MODE/SYNC pin,
the internal oscillator frequency changes to external clock
frequency (from original frequency based on RT setting)
after detecting 16 external clock edges. The external clock
logic-high level should be higher than 2.1V, logic-low level
lower than 0.8V and the pulse width of the external clock
should be more than 50ns. The RT resistor should be
selected to set the switching frequency at 10% lower than
the external clock frequency.
Table 1. Switching Frequency vs. RT
Resistor
SWITCHING FREQUENCY (kHz)
RT RESISTOR (kΩ)
400
51.1
500
OPEN
1000
19.1
2200
8.06
MAX17572
C1
C8
47pF
100pF R8
CLOCK
SOURCE
1K
RT/SYNC
R7
40.2K
VLOGIC-HIGH
VLOGIC-LOW
DUTY
Figure 1. External Clock Synchronization
Maxim Integrated │ 10
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage should be calculated as follows:
=
VIN(MIN)
VOUT + (I OUT(MAX) × (R DCR + 0.3))
+ (I OUT(MAX) × 0.35)
1 − (f SW(MAX) × t OFF(MAX) )
VIN(MAX) =
VOUT
f SW(MAX) × t ON(MIN)
Where VOUT is the steady-state output voltage, IOUT (MAX)
is the maximum load current, RDCR is the DC resistance of
the inductor, fSW(MAX) is the maximum switching frequency,
tOFF(MAX) is the worst-case minimum switch off-time (160ns)
and tON-MIN is the worst-case minimum switch on-time
(80ns).
Overcurrent Protection
The device is provided with a robust overcurrent protection
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 1.75A (typ).
A runaway current limit on the high-side switch current
at 2A (typ) protects the device under high input voltage,
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 runaway current limit triggers a hiccup
mode. In addition, if, due to a fault condition, feedback
voltage drops to 0.58V (typ) any time after soft-start is
complete, hiccup mode is triggered. In hiccup mode, the
converter is protected by suspending switching for a hiccup
timeout period of 32,768 clock cycles. Once the hiccup
timeout period expires, soft-start is attempted again.
Note that when soft-start is attempted under an overload
condition, if the feedback voltage does not exceed 0.58V,
the device switches at half the programmed switching
frequency. Hiccup mode of operation ensures low power
dissipation under output short-circuit conditions.
RESET Output
The device includes a RESET comparator to monitor the
output voltage. The open-drain RESET output requires an
external pullup resistor. RESET goes high (high impedance)
1024 switching cycles after the regulator output increases
above 95% of the designed nominal regulated voltage.
RESET goes low when the regulator output voltage drops
to below 92% of the nominal regulated voltage. RESET
also goes low during thermal shutdown.
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Prebiased Output
When the device starts into a prebiased output, both the
high-side and 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. The
output voltage is then smoothly ramped up to the target
value in alignment with the internal reference.
Thermal Shutdown Protection
Thermal shutdown protection limits total power dissipation 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 thermal
sensor turns the device on again after the junction
temperature cools by 10°C. Soft-start resets during
thermal shutdown. Carefully evaluate the total power
dissipation (see the Power Dissipation section) to avoid
unwanted triggering of the thermal shutdown protection in
normal operation.
Typical Application Circuit
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 (IRMS) is defined by the
following equation:
=
IRMS I OUT(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:
C IN =
I OUT(MAX) × D × (1 − D)
η × f SW × ∆VIN
where D = VOUT/VIN is the duty ratio of the controller,
fSW is the switching frequency, ∆VIN is the allowable input
voltage ripple, and η is the efficiency.
Maxim Integrated │ 11
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
In applications where the source is located distant from
the device input, an 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.
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=
2 × VOUT
f SW
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.
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to their
stability over temperature in industrial applications. The
output capacitors are usually sized to support a step load
of 50% of the maximum output current in the application,
so the output voltage deviation is contained to 3% of the
output voltage change. The minimum required output
capacitance can be calculated as follows:
C OUT =
The soft-start time (tSS) is related to the capacitor connected
at SS (CSS) by the following equation:
t SS =
C SS
5.55 × 10 −6
For example, to program a 2ms soft-start time, a 12nF
capacitor should be connected from the SS pin to GND.
Adjusting Output Voltage
Set the output voltage with a resistive voltage-divider connected
from the positive terminal of the output capacitor (VOUT)
to SGND (see Figure 2). Connect the center node of
the divider to the FB pin. Use the following procedure to
choose the resistive voltage-divider values:
Calculate resistor R4 from the output to the FB pin as
follows:
R4 =
1850
C OUT_SEL
Where COUT_SEL (in µF) is the actual derated value of
the output capacitance used and R4 is in kΩ. The minimum
allowable value of R4 is (5.6 x VOUT), where R4 is in kΩ.
If the value of R4 calculated using the above equation
is less than (5.6 x VOUT), increase the value of R4 to at
least (5.6 x VOUT).
R5 =
R4 × 0.9
(VOUT − 0.9)
R5 is in kΩ.
60
VOUT
Where COUT is in µF. Derating of ceramic capacitors with
DC-voltage must be considered 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 GND programs the soft-start time. The selected
output capacitance (CSEL) and the output voltage (VOUT)
determine the minimum required soft-start capacitor as
follows:
VOUT
R4
FB
R5
SGND
Figure 2. Adjusting Output Voltage
C SS ≥ 56 × 10 −6 × C SEL × VOUT
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Maxim Integrated │ 12
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Setting the 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 VIN to SGND.
Connect the center node of the divider to EN/UVLO.
Choose R1 to be 3.3MΩ and then calculate R2 as follows:
R2 =
1.215 × R1
(VINU − 1.215)
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 signal source output and the EN/UVLO
pin, to reduce voltage ringing on the line.
Power Dissipation
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as follows:
(
R1
EN/UVLO
R2
where VINU is the voltage at which the device is required
to turn on. Ensure that VINU is higher than 0.8 x VOUT.
1
PLOSS
= (POUT × ( − 1)) − I OUT 2 × R DCR
η
P=
OUT VOUT × I OUT
VIN
)
Where POUT is the output power, η is the efficiency of the
converter and RDCR is the DC resistance of the inductor
(see the 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:
θ JA = 41°C / W
θ JC = 8.5°C / W
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA_MAX)
from the following equation:
TJ_MAX
= T A _MAX + (θ JA × 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, the junction temperature of the device can be
estimated at ayn given maximum ambient temperature as:
T=
J_MAX TEP_MAX + (θ JC × PLOSS )
SGND
Figure 3. Setting the Input Undervoltage Lockout
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 VIN 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 VCC pin also
should be placed close to the pin to reduce effects of trace
impedance.
When routing the circuitry around the IC, the analog smallsignal 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, typically
the return terminal of the VCC bypass capacitor. 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 vias 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 MAX17572 evaluation kit layout available at
www.maximintegrated.com.
Junction temperatures greater than +125°C degrades
operating lifetimes.
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Maxim Integrated │ 13
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Typical Application Circuit
VIN
VIN
BST
C5
0.1µF
C1
2.2µF
PGND
R3
4.7Ω
PGND
EXTV CC
VCC
VOUT
5V/1A
LX
EN/UVLO
C3
2.2µF
L1
15µH
C2
10µF
C6
0.1µF
MAX17572
R1
178KΩ
FB
RT/SYNC
R2
39KΩ
GND
R4
40.2KΩ
RESET
C4
5600 pF
SS
EP
L1 = XAL4040-153, 4mm x 4mm
Figure 4. Typical Application Circuit for 5V Output
VIN
VIN
BST
C5
0.1µF
C1
2.2µF
PGND
LX
EN/UVLO
PGND
C3
2.2µF
L1
15µH
MAX17572
C2
22µF
VOUT
3.3V/1A
R1
86.6KΩ
EXTV CC
VCC
FB
RT/SYNC
R2
32.4KΩ
GND
R4
40.2KΩ
RESET
C4
5600 pF
SS
EP
L1 = XAL4040-153, 4mm x 4mm
Figure 5. Typical Application Circuit for 3.3V Output
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Maxim Integrated │ 14
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Ordering Information
PART
Package Information
PIN-PACKAGE
PACKAGE-SIZE
12 TDFN
3mm x 3mm
MAX17572ATC+
+Denotes a lead(Pb)-free/RoHS-compliant package.
Chip Information
PROCESS: BiCMOS
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
12-TDFN EP* TD1233+1C
*Denotes exposed pad.
www.maximintegrated.com
OUTLINE
NO.
LAND
PATTERN NO.
21-0664
90-0397
Maxim Integrated │ 15
MAX17572
4.5V–60V, 1A, High-Efficiency, Synchronous
Step-Down DC-DC Converter
with Internal Compensaton
Revision History
REVISION
NUMBER
REVISION
DATE
0
9/16
DESCRIPTION
Initial release
PAGES
CHANGED
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For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
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.
© 2016 Maxim Integrated Products, Inc. │ 16