Smallest 1A, 1.4MHz Step-Down Regulators

8

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Pin Description

NAME

PIN

MAX1973

MAX1974

FUNCTION

1

FBSEL

FBSEL

Feedback-Mode Selector. Connect FBSEL to GND to set the output voltage to 1.8V

(MAX1973) or 1V (MAX1974). Connect FBSEL to IN to set the output voltage to 2.5V

(MAX1973) or 1.5V (MAX1974). Leave FBSEL unconnected to set the output voltage

using a resistor-divider at FB.

2

COMP

COMP

Compensation. Connect a series RC network to GND. COMP is internally pulled to

GND when the device is in shutdown or in undervoltage lockout (see the Compen-

sation Components section).

3FB

FB

Feedback Input. Connect to the output if a preset voltage is used, or to a resistor-

divider from the output to GND for an adjustable output voltage.

4SS

SS

Soft-Start Pin and Reference Output. Bypass to GND with at least 0.01µF. Connect

0.1µF to GND for a soft-start ramp time of 6.25ms for the MAX1973, or 3.75ms for the

MAX1974. SS is internally pulled to GND when the device is shut down or in

undervoltage lockout.

5

GND

GND

Ground

CTL2

—

Control Input 2. Controls enable/disable and voltage margining (see Table 1).

6

—

POK

Power-OK Output. Open-drain output goes low when output is below 90% of nominal

output. POK is also low when the device is shut down or in undervoltage lockout.

7

PGND

PGND

Power Ground

8

LX

LX

Inductor Connection. Connect an inductor from LX to the output.

9IN

IN

Input Supply Voltage. Input voltage range is 2.6V to 5.5V. Connect a 4.7µF capacitor

from IN to PGND.

CTL1

—

Control Input 1. Controls Enable/Disable and voltage margining (see Table 1).

10

—

ON

Enable Input. Connect to IN or drive high for normal operation. Drive low to put device

in shutdown.

MAX1974 WITH 100k

Ω PULLUP RESISTOR

MAX1974

POK AND INPUT VOLTAGE

2V/div

0

MAX1973/74 toc15

20ms/div

1V/div

2V/div

0

0

MAX1973

VOLTAGE MARGIN STEP CHANGE RESPONSE

1V/div

0

MAX1973/74 toc14

500mA/div

1ms/div

0

10V/div

0

10V/div

0

Typical Operating Characteristics (continued)