With dual, synchronized, out-of-phase operation, the

MAX1858A/MAX1875A/MAX1876As’ high-side MOSFETs

turn on 180° out-of-phase. The instantaneous input cur-

rent peaks of both regulators no longer overlap, resulting

in reduced RMS ripple current and input voltage ripple.

This reduces the required input capacitor ripple-current

rating, allowing fewer or less expensive capacitors, and

reduces shielding requirements for EMI. The Out-of-

Phase Waveforms in the Typical Operating Charac-

teristics demonstrate synchronized 180° out-of-phase

operation.

All MAX1858A/MAX1875A/MAX1876A functions are

internally powered from an on-chip, low-dropout 5V

regulator. The maximum regulator input voltage (V+) is

typically 5V. The MAX1858A/MAX1875A/MAX1876A

also employs an undervoltage lockout circuit that dis-

should also be bypassed to GND with a 0.1µF capaci-

normal operation can resume.

Dual 180° Out-of-Phase Buck Controllers with

Sequencing/Prebias Startup and POR

8

_______________________________________________________________________________________

V+

BST1

DH1

LX1

DL1

BST2

DH2

LX2

DL2

FB1

COMP1

*IRF7811W

**OPTIONAL

FB2

COMP2

PGND

REF

GND

OSC

SYNC

CKO

ILIM1

ILIM2

EN

OFF

ON

RESET OUTPUT

CLOCK OUTPUT

RST (MAX1858A/

MAX1876A ONLY)

MAX1858A

MAX1875A

MAX1876A

0.22

µF

2

× 10µF

4

× 220µF

L1

1.1

µH

OUTPUT1

6V - 23V

0.1

µF

R1A

8.06k

Ω

R1B

10k

Ω

10k

Ω

5.9k

Ω

0.01

µF

100pF

0.22

µF

6800pF

100pF

8.2k

Ω

R2B

10k

Ω

96.5k

Ω

140k

Ω

R2A

15k

Ω

4.7

Ω

4.7

Ω

4.7

Ω

**

**

L2

1.1

µH

CMPSH-3A

4

× 220µF

2

× 10µF

OUTPUT2

0.1

µF

4.7

µF

0.1

µF

118k

Ω

D3

CMSSH-3

84.5k

Ω

D2

CMSSH-3

Figure 1. Standard 600kHz Application Circuit