SC4612 데이터 시트보기 (PDF) - Semtech Corporation

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SC4612

Wide Input Range High Performance Synchronous Buck Switching Controller

Semtech Corporation 

POWER MANAGEMENT

Applications Information (Cont.)

Below are examples of calculating the OCP trip voltages.

Low Side RDS_ON Current Limit

SC4612

2.75V

SC4612

Vin

Ra

DRV pin

ILIM pin

R3 R4

130k 260k

R1

2k

COMP

Rb

L

R2

+100mV

10k

PHASE pin

R Iload@Toff

load

C1

R5

C2

2pF

1 0k

5pF

OCP

1. Ra, Rb - Not installed:

2.75V − 100mV

R3

=

100mV − Vphase

R2

solving for: VPHASE = -100mV, therefore the circuit will trip @ RDS_ON x ILOAD = 100mV

2. To lower trip voltage - install Rb. For example: Rb = 13k

2.75V − 100mV

R3

=

100mV − Vphase

R2 || (Rb + R1)

solving for: VPHASE = -20mV, obviously more sensitive! RDS_ON x ILOAD = 20mV

3. To increase trip voltage - install Ra. For example: Ra = 800k; VDRIVE = 7.8V typ.

2.75V − 100mV

R3

+

Vdrive

Ra + R1

=

100mV − Vphase

R2

solving for: VPHASE = -200mV. Current limit has doubled compared to original conditions.

NOTE! Allow for tempco and RDS_ON variation of the MOSFET - see “overcurrent protection” information on page 11 in the

datasheet.

 2007 Semtech Corp.

11

www.semtech.com

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