4

LT1620/LT1621

PI FU CTIO S

Positive Input. Used as integration node for end-of-cycle

determination flag. Integration time constant is calculated

using 5k

Ω typical output impedance.

PROG2: Comparator Negative Input. Program node for

end-of-cycle determination typically used during voltage

mode operation. The comparator threshold is reached

when the current sense amplifier differential input voltage

GND: Ground Reference.

MODE: Comparator Open Collector Output. Output is logic

low when magnitude of current sense amplifier differential

companion PWM controller IC, facilitating current mode

loop control.

–

+

SENSE

AMPLIFIER

PROG

PROG2*

500

Ω

2.5k

–

+

SENSE

AVG

AVG2*

MODE*

LT1620/21 • FBD

–

+

5k

*AVAILABLE IN THE LT1620GN ONLY

+

–

+

–

SENSE

–

SENSE

+

PWM

CONTROLLER

END-OF-CYCLE

(ACTIVE LOW)

(

×1 GAIN)

(

×10 GAIN)

(

×20 GAIN)

CURRENT

SENSE

RESISTOR

GND

5V

Current Sense Amplifier

The current sense amplifier is a multiple output voltage

amplifier with an operational input common mode range

from 0V to 32V. The amplifier generates scaled output

voltages at the SENSE, AVG and AVG2 (available in

LT1620GN) pins. These output signal voltages are refer-

(Refer to the Functional Block Diagram)

The first output (SENSE) is a unity gain, level-shifted repre-

charger type applications, this output is used to drive the

current sense amplifier of the mated PWM controller IC.

The other two outputs (AVG and AVG2) are internally

connected to a transconductance amplifier and compara-

tor, respectively. The AVG output yields a gain of 10, and

the AVG2 output provides a gain of 20. These pins are