SS6578 ETC-unknow, SS6578 Datasheet - Page 8

• Manufacturer Part Number: SS6578
• Description: High Efficiency Step Down Dc/dc Controller
• Manufacturer: ETC-unknow

Rev.2.02 4/06/2004
APPLICATION INFORMATION
A. Start Up Design
In order to eliminate the over-shoot issue which
happens when Vout is under 5V, we offer two
solutions for the SS6578 as a buck controller.
1. Buck Converter with 12V<Vin<18V
When the SS6578 is used in a Buck Circuit
with V
a Zener diode D2 of 6.8V.
of MOSFET Q1. The smaller the resistor value,
the lower temperature rise. The resistor value is
determined by the reverse current rating of the
Zener diode. Refer to its databook for the
reverse current rating. Note that the current is
strictly limited by the spec.
A temperature rise of 1 C for Q1 results from the
addition of R1=680ohm, D2=6.8V to the original
condition (Vin=12V, Vout=3.3V and I
Yet, the efficiency of the system remains nearly
This solution will limit the temperature rise
OUT
<5V, add a resistor R1 of 680 ohm and
12V< +V
IN
<15V
+
C1
100
Rs
Fig. 10 DC/DC Buck Converter V
SSM4435
0.1 F
680
C2
R1
www.SiliconStandard.com
Q1
OUT
D2
6.8V
=1.5A).
D1
SS32
1
2
3
4
U1 SS6578
VIN
DUTY
SHDN
FB
L1 33 H
GND
CS+
The current-sense resistor Rs is used for
over-current protection. Due to concerns about
the power loss, cost, and size, many users do not
use Rs in their buck converter application.
Damage caused by unexpected current (over
rating current) could be done to Q1, U1 and the
circuits attached to V
For the calculation of Rs, please refer to the
formula of Rs in “Typical Application” above.
DRI
CS-
the same.
Note: The input voltage rating in this circuit is 12V
rather than 4V, and the rating can be varied
depending on the value of Zener diode D2.
Please refer to Fig3.
OUT
8
7
6
5
=3.3V
330 F
C4
+V
OUT
+
OUT
, 3.3V
R2
47K
R3
27K
when Rs is not used.
SS6578
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