5V/3.3V or Adjustable, 100% Duty-Cycle,

High-Efficiency, Step-Down DC-DC Controllers

6

_______________________________________________________________________________________

______________________________________________________________Pin Description

Ground

8

8

1.3V Reference Output. Can source 100µA. Bypass with 0.1µF.

4

4

Positive Supply Input. Bypass with 0.47µF.

5

5

Current-Sense Input. Connect current-sense resistor between V+ and CS. External

MOSFET is turned off when the voltage across the resistor equals the current-limit

trip level (around 100mV).

6

6

Gate Drive for External P-Channel MOSFET. EXT swings between V+ and GND.

7

7

Active-High Shutdown Input. Device is placed in shutdown when SHDN is driven

high. In shutdown mode, the reference, output, and external MOSFET are turned off.

Connect to GND for normal operation.

3

3

3.3V or 5V Selection. Output voltage is set to 3.3V when this pin is low or 5V when it

is high.

—

2

Feedback Input for adjustable-output operation. Connect to an external voltage

divider between the output and GND (see the

Setting the Output Voltage section).

2

—

Sense input for fixed 5V or 3.3V output operation. OUT is internally connected to an

on-chip voltage divider (MAX1626). It does not supply current. Leave OUT uncon-

nected during adjustable-output operation (MAX1627).

1

1

GND

REF

V+

CS

EXT

SHDN

3/5

FB

OUT

MAX1626

C5

0.47

µF

P

D1

0.04

Ω

U1

LOGIC-LEVEL MOSFET

C4

0.1

µF

3/5

SHDN

REF

V+

EXT

CS

GND

OUT

INPUT

L1

22

µH, 3A

C1

220

µF

LOW-ESR

TANTALUM

C2

68

µF LOW-ESR

TANTALUM

C3

68

µF LOW-ESR

TANTALUM

L1: SUMIDA CDRH125-220

D1: NIHON NSQ03A03

U1: MORTOLA MMSF3PO2HD

OUTPUT

Figure 1. MAX1626 Typical Operating Circuit

MAX1626

MAX1627

MINIMUM ON-TIME

ONE-SHOT

S

OUT

(FB)

3/5

R3

R2

R1

SHDN

V+

CS

R

TRIG

Q

Q

MINIMUM OFF-TIME

ONE-SHOT

CURRENT-SENSE

COMPARATOR

ERROR

COMPARATOR

REF

1.5V

EXT

REF

( ) MAX1627 ONLY

MAX1626 ONLY

TRIG

Q

Figure 2. Simplified Functional Diagram

PIN

MAX1626

FUNCTION

MAX1627

NAME