Datasheet

Evaluates: MAX8655/MAX8688
MAX8655 Evaluation Kit
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Quick Start
Recommended Equipment
Before beginning, the following equipment is needed:
• MAX8655 EV kit
• Up to 12V at 5A adjustable DC power supply
• Digital multimeters (DMM)
• Up to 20A load
• Ammeter (optional)
Procedure
The MAX8655 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 output to 12V. Turn off the
power supply.
2) Verify that there is a shunt across the pins of jumper
JP2 (SCOMP and GND).
3) Verify that there is a shunt across pins 2-3 of
jumper JP8 (MODE and GND).
4) Verify that there is a shunt across jumper JP5 (AVL
and REFIN).
5) Connect the positive lead of the power supply to
the VIN pad of the JP1 terminal block and connect
the negative lead of the power supply to the GND
pad of the JP9 terminal on the EV kit.
6) Connect the positive lead of the DMM to the VOUT
pad and connect the negative lead of the DMM to
the GND pad on the EV kit.
7) Turn on the power supply.
8) Verify that the output voltage is 1.2V at the out-
put (between JP3 and JP9 terminals) of the
MAX8655_MAX8688 EV board.
9) Connect the load between VOUT and GND.
10) Verify that the voltage at VOUT is approximately
1.2V.
Detailed Description of Hardware
The MAX8655 EV kit operates from a 10.8V to 13.2V
input and generates an output voltage of 1.2V at loads
up to 20A.The MAX8655 EV kit features a circuit of a
step-down regulator operating on a PWM, peak cur-
rent-mode control scheme. Integrated power
MOSFETs provide a small footprint, ease of layout, and
reduced EMI.
The EV kit features an FSYNC pad to allow the convert-
er to synchronize with an external clock. See the
Evaluating Other Switching Frequencies and External
Clock Synchronization (FSYNC and SYNCO) section.
Evaluating Other Output Voltages
The output voltage of the MAX8655 can be adjusted
from 0.7V (min) to 5.5V (max). To set the output voltage
for the MAX8655, connect FB to the center of an exter-
nal resistor-divider from the output to GND (R8 and R10
of the MAX8655 EV kit). Select R10 between 5kΩ and
24kΩ, and then calculate R8 with the following equation:
where V
FB
= 0.7V or V
REFIN
. Resistors R8 and R10
should be placed as close as possible to the IC.
Refer to the MAX8655 IC data sheet to calculate other
associated components.
Evaluating Other Switching Frequencies
and External Clock Synchronization
(FSYNC and SYNCO)
The MAX8655 has an adjustable internal oscillator that
can be set to any frequency from 200kHz to 1MHz. To
set the switching frequency, connect a resistor
(R
FSYNC
) from FSYNC to GND. R
FSYNC
is calculated as:
where f
S
is the desired switching frequency in kilohertz.
The MAX8655 can also be synchronized to an external
clock by connecting the clock signal to FSYNC. A syn-
chronization output (SYNCO) generates a clock signal
that is 180° out-of-phase, which allows for another
MAX8655 to be synchronized 180° out-of-phase with
the first, by connecting SYNCO of the first MAX8655 to
FSYNC of the second to reduce the input ripple current.
Undervoltage Lockout (UVLO)
When V
AVL
drops below 4.03V, the MAX8655 assumes
that the supply voltage is too low to make valid
decisions, so the undervoltage-lockout (UVLO) circuitry
inhibits switching and turns off both internal power
MOSFETs. When V
AVL
rises above 4.15V, the reg-
ulator enters the startup sequence and then resumes
normal operation.
R
f
FSYNC
s
=−
30600
9 914.
RR
V
V
OUT
FB
810 1=× −
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