UCC1837

UCC2837

UCC3837

SLUS228A - AUGUST 1999

FEATURES

• On Board Charge Pump to Drive

External N-MOSFET

• Input Voltage as Low as 3V

• Duty Ratio Mode Over Current

Protection

• Extremely Low Dropout Voltage

• Low External Parts Count

• Output Voltages as Low as 1.5V

8-Pin N-FET Linear Regulator Controller

1

5

2

8

6

3

4

7

CHARGE

PUMP

CAP

LEVEL

SHIFT

1.5V REF

UVLO

TIMER

CURRENT SENSE

COMPARATOR

COMP

CT

CS

VDD

CURRENT SENSE

AMPLIFIER

VOUT

FB

GND

100mV

140mV

ERROR AMPLIFIER

BLOCK DIAGRAM

UDG-99145

DESCRIPTION

The UCC3837 Linear Regulator Controller includes all the features re-

quired for an extremely low dropout linear regulator that uses an external

N-channel MOSFET as the pass transistor. The device can operate from

input voltages as low as 3V and can provide high current levels, thus pro-

viding an efficient linear solution for custom processor voltages, bus ter-

mination voltages, and other logic level voltages below 3V. The on board

charge pump creates a gate drive voltage capable of driving an external

N-MOSFET which is optimal for low dropout voltage and high efficiency.

The wide versatility of this IC allows the user to optimize the setting of

both current limit and output voltage for applications beyond or between

standard 3-terminal linear regulator ranges.

This 8-pin controller IC features a duty ratio current limiting technique that

provides peak transient loading capability while limiting the average

power dissipation of the pass transistor during fault conditions. See the

Application Section for detailed information.