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MAX25255 Dual Phase

Evaluation Kit

Evaluates: MAX25254, MAX25255

Detailed Description of Hardware

The MAX25255 dual phase EV kit provides a proven

layout for the MAX25255 synchronous buck regulator IC.

The IC accepts input voltages as high as 36V and delivers

up to 12A. The EV kit can handle an input supply transient

up to 42V. Various test points are included for evaluation.

External Synchronization

The IC can operate in two modes: forced-PWM (FPWM)

or skip mode. Skip mode has better efficiency for light-

load conditions. When SYNC is pulled low, the IC oper-

ates in skip mode for light loads and PWM mode for larger

loads. When SYNC is pulled high, the IC is forced to oper-

ate in PWM mode across all load conditions.

SYNC can be used to synchronize with an external clock

signal. The IC is forced to operate in FPWM mode when

SYNC is connected to a clock source.

Buck Output Monitoring (PGOOD_)

The EV kit provides two power-good output test points

(PGOOD1 and PGOOD2) to monitor the status of the

buck output voltage VOUT and master status. The

PGOODs are pulled to high impedance when the output

voltage is in regulation. PGOODs pulled to ground when

the output voltage drops below 95% (typ) of its nominal

regulated voltage.

Programming Buck Output Voltage

The EV kit comes installed with MAX25255DAFDA/VY+,

which provides fixed 3.3V voltage regulation on VOUT.

To externally adjust the voltage at VOUT from 0.8V to

14V, remove U1 MAX25255DAFDA/VY+ and replace with

adjustable version IC, remove R5 and install a 0Ω resistor

on R7, place appropriate resistors in the positions R8 and

R9 according to the following equation:

VOUT

R8 R9

1

VFB







=

−













Where typically VFB = 0.8V(typ) and R9 = 10kΩ.

Selecting EXTVCC

The MAX25255 IC provides an internal 1.8V BIAS LDO

that supplies the IC internal circuitry. To reduce the IC

internal power dissipation, the input of the internal BIAS

LDO can be switched from VSUPF to an external sup-

ply or one of the buck converter outputs by applying

the voltage to EXTVCC. The EV kit provides jumper

JU_EXTVCC, which allows shunts to be installed con-

necting EXTVCC to VOUT. If the buck converter output is

connected to EXTVCC, light-load efficiency is improved

as the supply current to BIAS LDO is scaled down propor-

tionally to the duty cycle of the buck converter.

If the EXTVCC voltage drops below 2.40V (typ), the input

supply of the BIAS LDO is automatically switched back

to VSUPF.

Evaluating Other Variants

The EV kit comes installed with the 3.3V/2MHz/12A vari-

ant (MAX25255DAFDA/VY+). The other variants can be

installed with minimal component changes.

Analog Devices offers additional variations, including

the ICs that operate at the lower switching frequency

of 400kHz for increased efficiency. See the MAX25255

Dual Phase EV Kit Bill of Materials to select components

for evaluating 400kHz variants. Refer to the MAX25254/

MAX25255 IC data sheet for part variant details and

contact the factory for additional variants of MAX25254/

MAX25255.

Table 1. Default Jumper Settings

#Denotes RoHS compliance.

Ordering Information

JUMPER

SHUNT POSITION

FUNCTIONS

JU_EN1

1-2

BUCK1 ENABLED

JU_EN2

1-2

BUCK2 ENABLED

JU_SYNC

1-2

SYNC is pulled to BIAS to enable FPWM mode

JU_EXTVCC

Installed

EXTVCC is connected to VOUT

JU_PGOOD1

Installed

PGOOD1 is pulled up to BIAS when VOUT is in regulation

JU_PGOOD2

Installed

PGOOD2 is pulled up to BIAS when VOUT is in regulation

PART

TYPE

MAX25255DUALEVKIT# 3.3V/2MHz Dual Phase EV Kit