5V-to-3.3V, Synchronous, Step-Down

Power-Supply Controller

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5

______________________________________________________________Pin Description

16

NAME

FUNCTION

1

CS

Current-sense input: +100mV = nominal current-limit level referred to FB.

2

SS

Soft-start input. Ramp time to full current limit is 1ms/nF of capacitance to GND.

3

ON

ON/O

—

F

—

F

–

PIN

DL

Gate-drive output for the low-side synchronous rectifier MOSFET

4–7, 11

GND

Low-current analog ground. Feedback reference point for the output.

8

REF

3.3V internal reference output. Bypass to GND with 0.22µF minimum capacitor.

9

SYNC

300kHz. For external clock synchronization in the 240kHz to 350kHz range, a high-to-low transition

causes a new cycle to start.

10, 14, 15

Supply voltage input: 4.5V to 5.5V

17

BST

Boost capacitor connection (0.1µF)

12

N.C.

No internal connection

13

PGND

Power ground

18

LX

Inductor connection. Can swing 2V below GND without latchup.

19

DH

Gate-drive output for the high-side MOSFET

20

FB

Feedback and current-sense input for the PWM

OUTPUT

3.3V

LX

DL

GND

SS

MAX767

ON

VCC

REF

L1

BST

DH

D2

PGND

CS

FB

SHUTDOWN

ON/OFF

N1

N2

D1

SMALL-

SIGNAL

SCHOTTKY

C1

R1

C3

0.1

µF

C2

C6

0.22

µF

C5

(OPTIONAL)

SYNC

R2

10

Ω

INPUT

4.5V TO 5.5V

0.01

µF

C4

4.7

µF

Figure 1. Standard Application Circuit