MIC2172/3172

100kHz 1.25A Switching Regulators

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (

April 2006

M9999-041806

(408) 955-1690

General Description

The MIC2172 and MIC3172 are complete 100kHz SMPS

current-mode controllers with internal 65V 1.25A power

switches.

The

MIC2172

features

external

frequency

synchronization

or

frequency

adjustment,

while

the

MIC3172 features an enable/shutdown control input.

Although

primarily

intended

for

voltage

step-up

applications,

the

floating

switch

architecture

of

the

MIC2172/3172 makes it practical for step-down, inverting,

and Cuk configurations as well as isolated topologies.

Operating from 3V to 40V, the MIC2172/3172 draws only

7mA of quiescent current making it attractive for battery

operated supplies.

The MIC3172 is for applications that require on/off control

of the regulator. The MIC3172 is externally shutdown by

applying a TTL low signal to EN (enable). When disabled,

the MIC3172 draws only leakage current (typically less

than 1µA). EN must be high for normal operation. For

TTL high.

The MIC2172 is for applications requiring two or more

SMPS regulators that operate from the same input supply.

The MIC2172 features a SYNC input which allows locking

of its internal oscillator to an external reference. This

makes it possible to avoid the audible beat frequencies

that result from the unequal oscillator frequencies of

independent SMPS regulators.

A reference signal can be supplied by one MIC2172

designated as a master. To insure locking of the slave’s

oscillators, the reference oscillator frequency must be

higher than the slave’s. The master MIC2172’s oscillator

frequency is increased up to 135kHz by connecting a

resistor

from

SYNC

to

ground

(see

applications

information).

The MIC2172/3172 is available in an 8-pin plastic DIP or

SOIC for –40

°C to +85°C operation.

Features

• 1.25A, 65V internal switch rating

• 3V to 40V input voltage range

• Current-mode operation

• Internal cycle-by-cycle current limit

• Thermal shutdown

• Low external parts count

• Operates in most switching topologies

• 7mA quiescent current (operating)

• <1µA quiescent current, shutdown mode (MIC3172)

• TTL shutdown compatibility (MIC3172)

• External frequency synchronization (MIC2172)

• External frequency trim (MIC2172)

• Fits most LT1172 sockets (see applications info)

Applications

• Laptop/palmtop computers

• Toys

• Hand-held instruments

• Off-line converter up to 50W (requires external power

switch)

• Predriver for higher power capability

• Master/slave configurations (MIC2172)

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