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MAX17574 3.3V Output
Evaluation Kit
Evaluates: MAX17574
3.3V Output-Voltage Application
General Description
The MAX17574 3.3V output evaluation kit (EV kit) provides
a proven design to evaluate the MAX17574 high-voltage,
high-efficiency, synchronous step-down DC-DC converter.
The EV kit is preset for 3.3V output at load currents up
to 3A and features a 500kHz switching frequency for
optimum efficiency and component size. The EV kit
features adjustable input undervoltage lockout, adjustable
soft-start, open-drain
RESET
signal, and external
frequency synchronization.
Quick Start
Recommended Equipment
●
MAX17574 3.3V output EV kit
●
5V to 60V, 5A DC input power supply
●
Load capable of sinking 3A
●
Digital voltmeter (DVM)
Procedure
Features
●
Operates from a 5V to 60V Input Supply
●
3.3V Output Voltage
●
Up to 3A Output Current
●
500kHz Switching Frequency
●
Enable/UVLO Input, Resistor-Programmable UVLO
Threshold
●
Adjustable Soft-Start Time
●
MODE/SYNC Pin to Select Among PWM, PFM, or
DCM Modes
●
Open-Drain RESET Output
●
External Frequency Synchronization
●
Overcurrent and Overtemperature Protection
●
Proven PCB Layout
●
Fully Assembled and Tested
Ordering Information
appears at end of data sheet.
The EV kit is fully assembled and tested. Follow the steps
below to verify the board operation.
Caution: Do not turn
on power supply until all connections are completed.
1)
2)
Set the power supply at a voltage between 5V and
60V. Disable the power supply.
Connect the positive terminal of the power supply to
the VIN PCB pad and the negative terminal to the
nearest PGND PCB pad. Connect the positive
terminal of the 3A load to the VOUT PCB pad and the
negative terminal to the nearest PGND PCB pad.
Connect the DVM across the VOUT PCB pad and the
nearest PGND PCB pad.
Verify that shunts are installed across pins 1-2 on
jumper JU1 (see
Table 1
for details).
Select the shunt position on jumper JU2 according to
the intended MODE/SYNC of operation (see
Table 2
for details).
Turn on the DC power supply.
Enable the load.
Verify that the DVM displays 3.3V.
3)
4)
5)
6)
7)
8)
19-8701; Rev 2; 5/18
MAX17574 3.3V Output
Evaluation Kit
Detailed Description
Evaluates: MAX17574
3.3V Output-Voltage Application
MODE/SYNC Selection (MODE/SYNC)
The MAX17574 3.3V output EV kit provides a proven
design to evaluate the MAX17574 high-voltage, high-
efficiency, synchronous step-down DC-DC converter. The
EV kit is preset for 3.3V output from 5V to 60V input at
load currents up to 3A and features a 500kHz switching
frequency for optimum efficiency and component size.
The EV kit includes an EN/UVLO PCB pad and jumper
JU1 to enable the output at a desired input voltage. The
SYNC PCB pad allows an external clock to synchronize
the device. Jumper JU2 allows the selection of a particu-
lar MODE/SYNC of operation based on light-load perfor-
mance requirements. An additional
RESET
PCB pad is
available for monitoring whether the converter output is
in regulation.
The device’s MODE/SYNC pin can be used to select
among PWM, PFM, or DCM modes of operation. The
logic state of the MODE/SYNC pin is latched when the
V
CC
and EN/UVLO voltages exceed the respective UVLO
rising thresholds and all internal voltages are ready to
allow LX switching. State changes on the MODE/SYNC
pin are ignored during normal operation. Refer to the
MAX17574 IC data sheet for more information on PWM,
PFM, and DCM MODE/SYNC modes of operation.
Table 2
shows EV kit jumper settings that can be used to
configure the desired mode of operation.
External Clock Synchronization
(MODE/SYNC)
Soft-Start Input (SS)
The device utilizes an adjustable soft-start function to
limit inrush current during startup. The soft-start time is
adjusted by the value of C8, the external capacitor from
SS to GND. The selected output capacitance (C
SEL
) and
the output voltage (V
OUT
) determine the minimum value
of C8, as shown by the following equation:
C8 ≥ 28 x 10
-6
x C
SEL
x V
OUT
The soft-start time (t
SS
) is related to C8 by the following
equation:
t
SS
= C8/(5.55 x 10
-6
)
For example, to program a 1ms soft-start time, C8 should
be 5.6nF.
The internal oscillator of the device can be synchronized
to an external clock signal on the SYNC pin. The external
synchronization clock frequency must be between 1.1f
SW
and 1.4f
SW
, where f
SW
is the frequency of operation
set by R3. The minimum external clock high pulse width
should be greater than 50ns and the minimum external
clock low pulse width should be greater than 160ns.
Table 1. Regulator Enable (EN/UVLO)
Description (JU1)
SHUNT
POSITION
1-2*
Not
installed
2-3
EN/UVLO PIN
Connected to V
IN
Connected to the
center node of
resistor-divider R1
and R2
Connected to SGND
MAX17574_ OUTPUT
Enabled
Enabled, UVLO level
set through the R1 and
R2 resistors
Disabled
Regulator Enable/Undervoltage-Lockout
Level (EN/UVLO)
The device offers an adjustable input undervoltage-
lockout level. For normal operation, a shunt should be
installed across pins 1-2 on jumper JU1. To disable the
output, install a shunt across pins 2-3 on JU1 and the EN/
UVLO pin is pulled to GND. See
Table 1
for JU1 settings.
Set the voltage at which the device turns on with the resis-
tive voltage-divider R1/R2 connected from VIN to SGND.
Connect the center node of the divider to EN/UVLO.
Choose R1 to be 3.32MΩ and then calculate R2 as follows:
R2
=
R1
×
1.215
(V
INU
−
1.215)
*Default
position.
Table 2. MODE/SYNC Description (JU2)
SHUNT
POSITION
Not
installed*
2-3
1-2
MODE/SYNC
PIN
Unconnected
Connected to SGND
Connected to V
CC
MAX17574_ MODE
PFM mode of
operation
PWM mode of
operation
DCM mode of
operation
where V
INU
is the voltage at which the device is required
to turn on.
*Default
position.
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