MAXM17544 3.3V Output
Evaluation Kit
Evaluates: MAXM17544 in 3.3V
Output-Voltage Application
General Description
The MAXM17544 evaluation kit (EV kit) is a demonstration
circuit of the MAXM17544 high-voltage, high-efficiency,
current-mode scheme, synchronous step-down, DC-DC
switching power module. The EV kit is designed for a 3.3V
output and delivers up to 3.5A load current from a wide
input-voltage range of 4.5V to 42V. The EV kit switches at
an optimal 500kHz switching frequency to allow the use of
small component-sizes, helping to minimize solution-size
while maintaining high-performance. The EV kit provides
a precision-enable input, an open-drain
RESET
output
signal, and external frequency synchronization to provide
a simple and reliable startup sequence and eliminate beat
frequency between regulators. The EV kit also includes
optional component footprints to program different output
voltages, an adjustable input undervoltage-lockout, and
a soft-start time to control inrush current during startup.
The MAXM17544 IC data sheet provides a complete
description of the part that should be read in conjunction
with this evaluation kit data sheet prior to modifying the
demo circuit.
Ordering Information
appears at end of data sheet.
Features
● Highly Integrated Solution with Integrated Shield
Inductor
● Wide 4.5V to 42V Input Range
● Preset 3.3V Output with a Fixed Resistor-Divider on
FB (Feedback Pin)
● Programmable Output-Voltage Feature (0.9V to 12V)
● Up to 3.5A Output Current
● High 91.2% Efficiency (V
IN
= 12V, V
OUT
= 3.3V at 0.74A)
● 500kHz Switching Frequency
● Enable/UVLO Input, Resistor-Programmable UVLO
Threshold
● Adjustable Soft-Start Time
● Selectable PWM, PFM, or DCM Mode
● Open-Drain
RESET
Output
● External Frequency Synchronization
● Overcurrent and Overtemperature Protection
● Low-Profile, Surface-Mount Components
● Lead(Pb)-Free and RoHS Compliant
● Fully Assembled and Tested
PRELIMINARY
19-7625; Rev 0; 5/15
MAXM17544 3.3V Output
Evaluation Kit
Quick Start
Recommended Equipment
●
●
●
●
●
MAXM17544 EV kit
4.5V to 42V DC power supply (V
IN
)
Dummy load capable of sinking 3.5A
Digital voltmeter (DVM)
100MHz dual-trace oscilloscope
Evaluates: MAXM17544 in 3.3V
Output-Voltage Application
On the bottom layer, additional footprints of optional
components are included to ease board modification for
different input/output configurations.
Soft-Start Input (SS)
Procedure
The EV kit is fully assembled and tested. Follow the steps
below to verify board operation.
Caution: Do not turn on
the power supply until all connections are completed.
Set the power supply at a voltage between 4.5V and
42V. Disable the power supply.
2) Connect the positive and negative terminals of the
power supply to IN and PGND PCB pads, respectively.
3) Connect the positive and negative terminals of the
3.5A load to OUT and PGND2 PCB pads, respectively,
and set the load to 0A.
4) Connect the DVM across the OUT PCB pad and the
PGND2 PCB pad.
5) Verify that no shunts are installed across pin 1-2 on
jumper JU1 to enable UVLO (see
Table 1
for details).
6) Verify that a shunt is installed across JU3 to disable
the external synchronization (see
Table 3
for details).
7) Verify that a shunt is installed across JU2 to enable
PWM mode (see
Table 2
for details).
8) Enable the input power supply.
9) Verify the DVM displays 3.3V.
10) Increase the load up to 3.5A to verify the DVM continues
displaying 3.3V.
1)
The device utilizes an adjustable soft-start function to
limit inrush current during startup. The soft-start time is
programmed by the value of the external capacitor from
SS to GND (C1). The selected output capacitance (C
SEL
)
and the output voltage (V
OUT
) determine the minimum
value of C1, as shown by the following equation:
C1
≥
28
×
10
−
3
×
C
SEL
×
V
OUT
where C1 is in nF and C
SEL
is in µF
The soft-start time (t
SS
) is calculated by the equation
below:
t
SS
=
C1/ 5.55
where t
SS
is in ms and C1 is in nF.
PRELIMINARY
Programmable Undervoltage Lockout (UVLO)
Detailed Description of Hardware
The EV kit offers an adjustable-input undervoltage-
lockout level by resistor-dividers connected between
IN, EN/UVLO, and GND pins. For normal operation, a
shunt should not be installed across pins 1-2 on JU1
to enable the output through an internal pullup 3.3MΩ
resistor from the EN/UVLO pin to IN pin. To disable the
output, install the shunt across pins 1-2 on JU1 to
pull EN/UVLO pin to GND. See
Table 1
for JU1
jumper settings. The EV kit also provides an optional
R3 PCB footprint to program a UVLO threshold voltage
at which an input-voltage level device turns on. The R3
resistor can be calculated by the following equation:
R3
=
4009.5
(V
INU
−
1.215)
The EV kit is a proven circuit to demonstrate the high-
voltage, high-efficiency, and compact solution-
size of the synchronous step-down, DC-DC power
module. The output voltage is preset for 3.3V to operate
from 4.5V to 42V and provides up to 3.5A load current.
The optimal frequency is set at 500kHz to maximize
efficiency and minimize component size. The EV kit includes
jumpers JU1 to enable/disable UVLO of the device, JU2
to configure in PWM, PFM, or DCM mode in advantage
of light-load efficiency, and JU3 to enable/disable external
clock synchronize (SYNC). The
RESET
PCB pad is also
available for monitoring output voltage regulation to
enable/disable the application circuit of the load. The elec-
trolytic capacitor (C8) is required only when the V
IN
power
supply is situated far from device circuit. When R4 is
open, the device switches at 500kHz switching frequency.
where V
INU
is the input voltage at which the device is
required to turn on, and R3 unit is in kΩ.
Table 1. UVLO Enable/Disable
Configuration (JU1)
SHUNT
POSITION
Installed
Not installed*
*Default
position.
EN PIN
Connected to GND
Connected to VIN
MAXM17544_OUTPUT
Disable
Enable
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Maxim Integrated │ 2
MAXM17544 3.3V Output
Evaluation Kit
Mode Selection (MODE)
Evaluates: MAXM17544 in 3.3V
Output-Voltage Application
amplitude should be greater than 50ns and 2.1V, respectively.
The minimum external clock low pulse width should be
greater than 160ns, and the maximum external clock
low pulse amplitude should be less than 0.8V.
Table 3
describes the connection of the SYNC pin.
The device’s MODE pin can be used to select among
PWM, PFM, or DCM modes of operation in advance of
constant frequency or high efficiency at light loads. The
logic state of the MODE pin is latched when the VCC
and EN/UVLO voltage exceed the respective UVLO
rising thresholds and all internal voltages are ready
to allow LX switching. The changes on the MODE
pin are ignored during normal operation. Refer to the
MAXM17544 IC data sheet for more information on PWM,
PFM, and DCM modes of operation.
Table 2
shows EV kit
jumper settings that can be used to configure the desired
mode of operation.
Setting V
OUT
with a Resistive
Voltage Divider at FB
External Clock Synchronization (SYNC)
The internal oscillator of the device can be synchronized
to an external clock signal to eliminate beat frequency
between regulators through the SYNC pin. The external
synchronization clock frequency must be between 1.1f
SW
to 1.4f
SW
, where f
SW
is the frequency of operation set
by R5. The minimum external clock high pulse width and
The EV kit is preset for 3.3V and offers an adjustable
output voltage range as low as 0.9V up to 12V at 3.5A
maximum load. The adjustable output voltage can be
programmed by the set of resistor dividers R1 and R2.
Refer to the Table 1 (Selection Component Values) on the
MAXM17544 IC data sheet to select optimal component
values for each specific input voltage range from 4.5V
up to 42V and an output voltage from 0.9V up to 12V. To
obtain a different output voltage other than default setting
outputs in Table 1, only six component (R1, R2, C1–C3,
and C8) values need to be modified by the equation
described in the
Setting the Output Voltage
section in the
MAXM17544 IC data sheet.
PRELIMINARY
Table 2. MODE Description (JU2)
SHUNT
POSITION
Not
installed
1-2
2-3*
MODE PIN
Unconnected
Connected to VCC
Connected to GND
MAXM17544_MODE
PFM mode of operation
DCM mode of operation
PWM mode of operation
Table 3. SYNC Description (JU3)
SHUNT
POSITION
1-2*
Not
installed
*Default
position.
SYNC PIN
Connected to SGND
Connected to test
loop on PCB
MAXM17544_SYNC
SYNC feature unused
Frequency can be
synchronized with an
external clock
*Default
position.
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Maxim Integrated │ 3
MAXM17544 3.3V Output
Evaluation Kit
Typical Operating Characteristics
Evaluates: MAXM17544 in 3.3V
Output-Voltage Application
(V
IN
= 4.5V - 42V, V
OUT
= 3.3V, I
OUT
= 0 – 3.5A, T
A
= +25°C, unless otherwise noted.)
100
90
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, PFM MODE
toc01
100
90
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, PWM MODE
toc02
100
90
EFFICIENCY (%)
80
70
60
50
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, DCM MODE
toc03
80
70
60
50
40
V
IN
= 36V
f
SW
= 500kHz
80
70
60
50
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
V
IN
= 36V
f
SW
= 500kHz
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
V
IN
= 36V
f
SW
= 500kHz
MODE = V
CC
0
1000
2000
3000
PRELIMINARY
MODE = OPEN
0
1000
2000
3000
40
0
1000
2000
MODE = SGND
3000
40
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
3.6
3.5
V
OUT
(V)
3.4
3.3
3.2
3.1
3
LOAD REGULATION
V
OUT
= 3.3V, PFM MODE
V
IN
= 5.0V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
toc04
3.6
3.5
V
OUT
(V)
3.4
3.3
3.2
3.1
3
LOAD REGULATION
V
OUT
= 3.3V, PWM MODE
V
IN
= 5.0V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
toc05
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 36V
f
SW
= 500kHz
MODE = OPEN
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 36V
f
SW
= 500kHz
MODE = SGND
0
1000
2000
3000
0
1000
2000
3000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
3.6
3.5
V
OUT
(V)
3.4
3.3
3.2
3.1
3
LOAD REGULATION
V
OUT
= 3.3V, DCM MODE
V
IN
= 5.0V
f
SW
= 500kHz
V
IN
= 12V
f
SW
= 500kHz
toc06
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A TO 1.75A,
toc07
MODE = OPEN
I
OUT
2A/div
V
IN
= 24V
f
SW
= 500kHz
V
IN
= 36V
f
SW
= 500kHz
MODE = V
CC
V
OUT
200mV/div
(AC
COUPLED)
200µs/div
0
1000
2000
3000
OUTPUT CURRENT (mA)
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Maxim Integrated │ 4
MAXM17544 3.3V Output
Evaluation Kit
Typical Operating Characteristics (continued)
Evaluates: MAXM17544 in 3.3V
Output-Voltage Application
(V
IN
= 4.5V - 42V, V
OUT
= 3.3V, I
OUT
= 0 – 3.5A, T
A
= +25°C, unless otherwise noted.)
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A TO 1.75A,
MODE = SGND
toc08
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A TO 1.75A,
MODE = V
CC
toc09
I
OUT
2A/div
I
OUT
2A/div
V
OUT
200mV/div
(AC
COUPLED)
V
OUT
200mV/div
(AC
COUPLED)
200µs/div
PRELIMINARY
200µs/div
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 1.75A TO 3.5A,
MODE = SGND
toc10
CLOSED-LOOP BODE PLOT
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 3.5A,
MODE = SGND
50
40
PHASE
30
GAIN (dB)
20
10
0
-10
-20
-30
-40
-50
1k
CROSSOVER FREQUENCY = 52.56kHz
PHASE MARGIN = 66.7
◦
toc11
150.00
120.00
90.00
30.00
PHASE MARGIN (°)
60.00
0.00
-30.00
-60.00
-90.00
-120.00
2A/div
I
OUT
GAIN
V
OUT
200mV/div
(AC
COUPLED)
200µs/div
10k
100k
-150.00
1Meg
FREQUENCY (Hz)
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