SS6578 Datasheet, PDF (9/11 Pages) List of Unclassifed Manufacturers – HIGH EFFICIENCY STEP DOWN DC/DC CONTROLLER

+VIN = 5~18V
Rs
+
C1
100µF
R2
100K
Q1
SSM4435
D1
SS32
L1 33µH
D2
LL4148
C3
1µF
Q2
R1
3K3
*** R6
1M
C2
0.1uF
<15V
1 _VIN
2 _DUTY
3 _SHDN
4 _FB
CS+ ⁸
CS- ⁷
DRI ⁶
GND ⁵
U1 SS6578
+VOUT, 3.3V
+
C4
R3
470µF
47K
R4
27K
R7
*
* V_IN>15V, R7=15Ω
V_IN≤15V, R7=0Ω*
*** R6 can adjust the duty cycle max. It can be 0Ω
Fig 11. DC/DC Buck Converter V_OUT=3.3V
SS6578
B. Short Circuit Protection Design
1. As we 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.
2. Design1: shown as Fig. 12.
Method: Add a fast fuse to V_OUT.
A fuse can be selected to pass
the start up current, but open quickly
with a large unexpected current. Of
course, replacement of the fuse
is needed after short circuit.
3. 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 V_OUT ≥3V.
Rev.2.02 4/06/2004
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