6

LTC1550/LTC1551

REG: This is an open-drain output that pulls low when the

output voltage is within 5% of the set value. It will sink 7mA

to ground with a 5V supply. The external circuitry must

provide a pull-up or REG will not swing high. The voltage

ground without damage.

ADJ: For adjustable versions only, this is the feedback

point for the external resistor divider string. Connect a

connected to ADJ. Note that the resistor string needs to be

connected “upside-down” from a traditional negative regu-

lator. See the Applications Information section for hook-

up details.

NC: No Internal Connection.

–

+

–

+

S2

S3

S1

S4

C1

CLK

900kHz

SENSE

CHARGE

PUMP

LINEAR

REGULATOR

1550/51 BD

ADJ

REG

60mV

1.18V

*SHDN

*SHDN FOR LTC1550, SHDN FOR LTC1551

** FIXED OUTPUT VERSIONS ONLY

COMP2

**

**

+

1.24V

OVERVIEW

The LTC1550/LTC1551 are switched capacitor, inverting

charge pumps with internal linear post-regulators. The

LTC1550CS8/LTC1551CS8 provide a regulated, low ripple

– 4.1V output at up to 10mA load current from a single 5V

supply. The LTC1550CGN provides a regulated, low ripple

adjustable output. Output load current for the adjustable

version depends on the input/output voltage combination.

Consult the graph provided in the Typical Performance

Characteristics section and the Electrical Characteristics

table for guaranteed test points. The LTC1550/LTC1551

are ideal for use as bias voltage generators for GaAs

transmitter FETs in portable RF and cellular telephone

applications. The LTC1550 features an active-low

Shutdown pin (SHDN) that drops quiescent current to

below 1

µA. The LTC1551 is identical to the LTC1550,