Detailed Description

The MAX1955/MAX1956 are dual-output, fixed-frequency,

voltage-mode, PWM step-down controllers with 0.5%

output accuracy. Each controller switches at a constant

600kHz and is 180° out-of-phase with the other con-

troller, which reduces input ripple current and the num-

ber of input capacitors. Figure 1 is the functional

diagram.

An on-chip step-up bias supply generates a 5V gate

drive to deliver up to 25A output current per phase with

low-cost N-channel MOSFETs at up to 93% efficiency.

Lossless adjustable current limit eliminates expensive

current-sense resistors and improves efficiency.

Foldback current limit reduces power dissipation during

short-circuit condition and handles transient overloads

better than controllers using hiccup-mode short-circuit

protection.

1.6V to 5.5V Input, 0.5% Accurate, Dual

180° Out-of-Phase Step-Down Controllers

10

______________________________________________________________________________________

REF

1.28V

GND

GND1

COMP1

FB1

EN

SYNC

SEQ

COMP2

FB2

SOFT-

START DAC

VOLTAGE

MARGINING

AND

SHUTDOWN

OSCILLATOR

SEQUENCING

CONVERTER 2

VDD2

LXB

PGND

BST1

DH1

LX1

VDD1

DL1

PGND1

ILIM1

BST2

DH2

LX2

VDD2

DL2

PGND2

ILIM2

AVDD

IN

BIAS

UVLO

EA

R

S

Q

1V

5

µA

4V

PWM

x0.15

CONVERTER 1

BOOST

CONTROL

CURRENT LIMIT

AND

SHUTDOWN

Q

Figure 1. Functional Diagram