LT1620 データシートの表示（PDF） - Linear Technology

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LT1620

Rail-to-Rail Current Sense Amplifier

Linear Technology 

LT1620/LT1621

PI FU CTIO S

input (across external sense resistor) equal to (VCC –

VPROG)/10. Input voltage range is VCC to (VCC – 1.25V).

AVG2: Sense Amplifier AV = – 20 Output and Comparator

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

determination flag. Integration time constant is calculated

using 5kΩ 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

equals (VCC – VPROG2)/20. Input voltage range is (VCC –

0.15V) to (VCC – 2.5V).

GND: Ground Reference.

MODE: Comparator Open Collector Output. Output is logic

low when magnitude of current sense amplifier differential

input voltage is less than (VCC – VPROG2)/20.

IOUT: Transconductance Amplifier Output. In typical appli-

cation, IOUT sinks current from current-setting node on

companion PWM controller IC, facilitating current mode

loop control.

W

FUNCTIONAL BLOCK DIAGRA

5V

+–

CURRENT

SENSE

VID

RESISTOR

VCC

+–

500Ω

2.5k

IN+ +

SENSE

IN–

AMPLIFIER

–

PROG

5k

+

PROG2*

*AVAILABLE IN THE LT1620GN ONLY

–

GND

(×1 GAIN) SENSE

(×10 GAIN) AVG

(×20 GAIN) AVG2*

+

gm

–

IOUT

MODE*

LT1620/21 • FBD

INTVCC

SENSE+

SENSE–

PWM

CONTROLLER

ITH

END-OF-CYCLE

(ACTIVE LOW)

U

OPERATION (Refer to the Functional Block Diagram)

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-

enced to the VCC supply by pulling signal current through

internal VCC referred resistors.

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

sentation of the input signal (IN+ – IN–). In typical PWM/

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

4

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