LX2172/73

PRODUCT DA T ABOOK 1996/1997

Copyright © 1998

Rev. 0.4

a 12/04

4

GND

1

3

V

C

21

FB

3

2

SYNC

4

ENABLE

4

V

IN

55

E

1

6

V

SW

74

E

2

8

Signal ground. Keep separate from power grounds (E

Output of transconductance error amplifier. An R-C compensation network is connected from

this pin to the ground to stabilize the feedback loop. If this pin is pulled lower than 0.15V, the

IC goes into micropower mode.

Error amplifier inverting input. A resistor divider from the output of the converter to this pin sets

its nominal voltage.

LX2172 only. This pin is used to synchronize the device directly with a logic level input pulse.

External synchronization frequency must always be at a higher frequency than the minimum

internal clock. When not used, should be left open.

LX2173 only. This pin is the input to the enable comparator. A voltage under 1.4V will put the

device in micropower mode. Pin must be connected to V

Input supply voltage (3.0V to 25V).

Power return of first transistor (Q

This pin must be connected to ground.

Collector of output transistors. Connect to external inductor or input voltage, depending on circuit

topology.

Grounding this pin sets the current limit point to the maximum value. If pin is left open, the current

limit is set to half its maximum value.

Pin

Pin #

Pin #

Name

(8-pin Pkgs.) (5-pin TO-220)

Description

FUNCTIONAL PIN DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

FUNCTIONAL PIN DESCRIPTION

ELECTRICAL CHARACTERISTICS

Parameter

Symbol

Test Conditions

Units

LX2172 / 2173

Min.

Typ.

Max.

0.2

2

µsec

26

V

0.7

V

100

400

µA

15

µA

SYNC Pulse Width

SYNC Input HI

SYNC Input LO

SYNC Input Current HI

Input = 2V

SYNC Input Current LO

Input = 0.4V

SYNC Input Section (LX2172 only)

0.4

1.2

2.4

V

200

µA

100

µA

Enable Input Threshold

HI Input Current

Input = 2.4V

LO Input Current

Input = 0.4V

ENABLE Section (LX2173 only)