3

UC19432

UC29432

UC39432

UC39432B

COLL: The collector of the output transistor with a maxi-

mum voltage of 36V. This pin is the output of the

transconductance amplifier. The overall open loop volt-

where gm is designed to be –140mS ±30mS and RL rep-

resents the output load.

COMP: The output of the error amplifier and the input to

the transconductance amplifier. This pin is available to

compensate the high frequency gain of the error ampli-

fier. It is internally voltage limited to approximately 2.0V.

EA+: The non-inverting input to the error amplifier.

GND: The reference and power ground for the device.

The power ground of the output transistor is isolated on

the chip from the substrate ground used to bias the re-

mainder of the device.

ISET: The current set pin for the transconductance ampli-

fier. The transconductance will be –140mS as specified

in the electrical table if this pin is grounded. If a resis-

transconductance is calculated using the following equa-

tion: gm = –0.714V

will be approximately

I

V

R

MAX

L

=

+

06

51

.

.

Ω

REF: The output of the trimmed precision reference. It

can source or sink 10 A and still maintain the 1% tem-

perature specification.

SENSE: The inverting terminal of the error amplifier used

as both the voltage sense input to the error amplifier and

its other compensation point. The error amplifier uses the

SENSE input to compare against the 1.3V on-chip refer-

ence.

The SENSE pin is also used as the undervoltage lockout

(UVLO). It is intended to keep the chip from operating un-

til the internal reference is properly biased. The threshold

is approximately 1V. It is important that once the UVLO is

released,

the

error

amplifier

can

drive

the

transconductance amplifier to stabilize the loop. If a ca-

pacitor is connected between the SENSE and COMP

pins to create a pole, it will limit the slew rate of the error

amplifier. To increase the bandwidth and ensure startup

at low load current, it is recommended to create a zero

along with the pole as shown in the UC39431 shunt reg-

ulator application. The error amplifier must slew 2.0V to

drive the transconductance amplifier initially on.

VCC: The power connection for the device. The minimum

to maximum operating voltage is 2.2V to 36.0V. The qui-

escent current is typically 0.50mA.

PIN DESCRIPTIONS

Figure 1. 5.0V Optocoupler application.

UDG-95094