SS6578CSTB datasheet(9/11 Pages) SSC

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SS6578

VIN

DUTY

SHDN

GND

DRI

CS-

CS+

U1 SS6578

47K

27K

0.1uF

+VIN = 5~18V

+VOUT, 3.3V

470

µF

SS32

100

µF

µH

SSM4435

3K3

µF

LL4148

100K

<15V

***

VIN>15V, R7=15Ω

VIN≤15V, R7=0Ω*

***

R6 can adjust the duty cycle max. It can be 0

Ω

Fig 11. DC/DC Buck Converter VOUT=3.3V

B. Short Circuit Protection Design

know,

Short

Circuit

Protection

(abbreviated as SCP) does not always exist in

the DC-DC converter circuit. The fact is usually

the DC-DC converter provides the circuits

attached to VOUT with low power or low

voltage. Sometimes there is less concern about

safety, as the probability of short-circuit is

quite low. That gives users reasons to ignore

the use of an SCP circuit. However, we would still

like to point out the importance of the

protection. With SCP, the system will be well

protected in any situation. Two SCP circuits

are introduced as follows for your reference.

Design1: shown as Fig. 12.

Method: Add a fast fuse to VOUT.

A fuse can be selected to pass

the start up current, but open quickly

with a large unexpected current. Of

course,

replacement

the

fuse

is needed after short circuit.

Design 2: shown as Fig. 13.

Method: Add a SCP circuit

Note: 1. The time constant, which is

directly related to R1 and C1,

has a serious effect on the

circuit.

2. Circuit can be recovered by

removing the short circuit

event from the system.

3. The condition for applying

this design is VOUT ≥3V.

Rev.2.02 4/06/2004

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