參數(shù)資料
型號(hào): SS6578CNTR
廠商: Electronic Theatre Controls, Inc.
英文描述: HIGH EFFICIENCY STEP DOWN DC/DC CONTROLLER
中文描述: 高效率降壓DC / DC控制器
文件頁(yè)數(shù): 8/11頁(yè)
文件大?。?/td> 221K
代理商: SS6578CNTR
www.SiliconStandard.com 8 of 11
SS6578
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
OUT
<5V, add a resistor R1 of 680 ohm and
a Zener diode D2 of 6.8V.
This solution will limit the temperature rise
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
OUT
=1.5A).
Yet, the efficiency of the system remains nearly
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.
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
OUT
when Rs is not used.
For the calculation of Rs, please refer to the
formula of Rs in “Typical Application” above.
VIN
DUTY
SHDN
FB
U1
SS6578
1
2
3
4
GND
5
DRI
6
CS-
7
CS+
8
R2
47K
R3
27K
C2
0.1
μ
F
12V< +V
IN
<15V
+V
OUT
, 3.3V
+
C4
330
μ
F
D1
SS32
+
C1
100
μ
D2
6.8V
R1
680
Rs
Q1
SSM4435
L1
33
μ
H
Fig. 10 DC/DC Buck Converter V
OUT
=3.3V
Rev.2.0
2 4
/06/200
4
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