MAXM17545 3.3V Output
Evaluation Kit
Evaluates: MAXM17545 in 3.3V
Output-Voltage Application
General Description
The MAXM17545 evaluation kit (EV kit) is a demonstration
circuit of MAXM17545 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 1.7A load current from a wide input-
voltage range of 4.5V to 42V. The EV kit switches at an
optimal 400kHz 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
MAXM17545 IC data sheet provides a complete descrip-
tion of the part that should be read in conjunction with this
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 1.7A Output Current
● High 91.2% Efficiency (V
IN
= 12V, V
OUT
= 3.3V at 0.73A)
● 400kHz 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
19-7617; Rev 0; 5/15
MAXM17545 3.3V Output
Evaluation Kit
Quick Start
Recommended Equipment
●
●
●
●
●
MAXM17545 EV kit
4.5V to 42V DC power supply (V
IN
)
Dummy load capable of sinking 1.7A
Digital voltmeter (DVM)
100MHz dual-trace oscilloscope
Evaluates: MAXM17545 in 3.3V
Output-Voltage Application
components are included to ease board modification for
different input/output configurations.
Soft-Start Input (SS)
Procedure
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.
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.
1)
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
1.7A 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 pins 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 1.7A to verify the DVM
continues displaying 3.3V.
Programmable Undervoltage-Lockout (UVLO)
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
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 setting details. 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)
Detailed Description of Hardware
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 1.7A load current. The optimal fre-
quency is set at 400kHz to maximize efficiency and minimize
component size. The EV kit includes JU1 to enable/disable
UVLO of the device, JU2 to configure in PWM, PFM, or
DCM mode to improve 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 electrolytic capacitor (C8) is required only
when the V
IN
power supply is situated far from device
circuit. On the bottom layer, additional footprints of optional
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
MAXM17545_
OUTPUT
Disable
Enable
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│ 2
MAXM17545 3.3V Output
Evaluation Kit
Mode Selection (MODE)
Evaluates: MAXM17545 in 3.3V
Output-Voltage Application
Setting V
OUT
with a Resistive Voltage-Divider
at FB
The device’s MODE pin can be used to select among the
PWM, PFM, or DCM modes of operation in advance of
constant
frequency or high efficiency at light load. The
logic state of the MODE pin is latched when the V
CC
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 MAXM17545 IC
data sheet for more information on the 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.
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
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 EV kit is preset for 3.3V and offers an adjust-
able-output voltage range of 0.9V to 12V at 1.7A
maximum load. The adjustable output voltage can be
programmed by the set of resistor-dividers R1 and R2.
Refer to
Table 1
(Selection Component Values) of the
MAXM17545 IC data sheet to select optimal compo-
nent values for each specific input voltage range from
4.5V to 42V and an output voltage from 0.9V to 12V.
To obtain a different output voltage other than default
setting outputs in
Table 1,
only seven component (R1, R2,
R4, C1, C2, C3, and C8) values are needed to modify
the equation described in the
Setting the Output Voltage
section of the MAXM17545 IC data sheet.
Table 3. SYNC Description (JU3)
SHUNT
POSITION
1-2*
Not installed
*Default position.
SYNC PIN
Connected to
SGND
Connected to test
loop on PCB
MAXM17545_
SYNC
SYNC feature
unused
Frequency can be
synchronized with an
external clock
Table 2. MODE Description (JU2)
SHUNT
POSITION
Not installed
1-2
2-3*
*Default position.
MODE PIN
Unconnected
Connected to
VCC
Connected to
GND
MAXM17545_
MODE
PFM mode of
operation
DCM mode of
operation
PWM mode of
operation
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│ 3
MAXM17545 3.3V Output
Evaluation Kit
Typical Operating Characteristics
Evaluates: MAXM17545 in 3.3V
Output-Voltage Application
(V
IN
= 4.5V - 42V, V
OUT
= 3.3V, I
OUT
= 0 – 1.7A, T
A
= +25°C, unless otherwise noted.)
100
90
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, PFM MODE
toc01
100
90
EFFICIENCY (%)
80
70
60
50
40
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, PWM MODE
toc02
80
70
60
50
40
V
IN
= 24V,
f
SW
= 400kHz
V
IN
= 12V,
f
SW
= 400kHz
V
IN
= 36V,
f
SW
= 400kHz
MODE = OPEN
0
500
1000
1500
V
IN
= 24V,
f
SW
= 400kHz
V
IN
= 12V,
f
SW
= 400kHz
V
IN
= 36V,
f
SW
= 400kHz
MODE = SGND
0
500
1000
1500
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
100
90
EFFICIENCY (%)
80
70
60
50
40
EFFICIENCY vs. OUTPUT CURRENT
V
OUT
= 3.3V, DCM MODE
toc03
3.600
3.500
V
OUT
(V)
3.400
3.300
3.200
3.100
LOAD REGULATION
V
OUT
= 3.3V, PFM MODE
V
IN
= 5.0V
f
SW
= 400kHz
V
IN
= 12V
f
SW
= 400kHz
toc04
V
IN
= 24V,
f
SW
= 400kHz
V
IN
= 12V,
f
SW
= 400kHz
V
IN
= 36V,
f
SW
= 400kHz
MODE = V
CC
0
500
1000
1500
V
IN
= 24V
f
SW
= 400kHz
V
IN
= 36V
f
SW
= 400kHz
MODE = OPEN
3.000
0
500
1000
1500
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
3.6000
3.5000
V
OUT
(V)
3.4000
3.3000
3.2000
3.1000
3.0000
LOAD REGULATION
V
OUT
= 3.3V, PWM MODE
V
IN
= 5.0V
f
SW
= 400kHz
V
IN
= 12V
f
SW
=400kHz
toc05
3.6000
3.5000
V
OUT
(V)
3.4000
3.3000
3.2000
LOAD REGULATION
V
OUT
= 3.3V, DCM MODE
V
IN
= 5.0V
f
SW
= 400kHz
toc06
V
IN
= 12V
f
SW
= 400kHz
V
IN
= 24V
f
SW
= 400kHz
V
IN
= 36V
f
SW
= 400kHz
MODE = SGND
3.1000
3.0000
V
IN
= 24V
V
IN
= 36V
f
SW
= 400kHz f = 400kHz
SW
MODE = V
CC
0
500
1000
1500
OUTPUT CURRENT (mA)
0
500
1000
OUTPUT CURRENT (mA)
1500
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4
MAXM17545 3.3V Output
Evaluation Kit
Typical Operating Characteristics (continued)
Evaluates: MAXM17545 in 3.3V
Output-Voltage Application
(V
IN
= 4.5V - 42V, V
OUT
= 3.3V, I
OUT
= 0 – 1.7A, T
A
= +25°C, unless otherwise noted.)
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A - 0.85A,
MODE = OPEN
toc07
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A–0.85A,
MODE = SGND
toc08
I
OUT
1A/div
I
OUT
1A/div
V
OUT
100mV/div
(AC
COUPLED)
V
OUT
100mV/div
(AC
COUPLED)
200µs/div
200µs/div
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.05A–0.85A,
MODE = V
CC
toc09
LOAD CURRENT TRANSIENT RESPONSE
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 0.85A–1.7A,
MODE = SGND
toc10
I
OUT
1A/div
I
OUT
1A/div
V
OUT
100mV/div
(AC
COUPLED)
V
OUT
100mV/div
(AC
COUPLED)
200µs/div
200µs/div
50
40
30
GAIN (dB)
20
10
0
-10
-20
-30
-40
-50
CLOSED-LOOP BODE PLOT
V
IN
= 24V, V
OUT
= 3.3V, I
OUT
= 1.7A,
MODE = SGND
PHASE
toc11
150
120
90
30
PHASE MARGIN (°)
60
0
-30
-60
-90
-120
GAIN
1k
10k
100k
-150
1Meg
FREQUENCY (Hz)
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