SC1409 데이터 시트보기 (PDF) - Semtech Corporation
부품명
상세내역
제조사
SC1409 Datasheet PDF : 8 Pages
| |||
June 28, 2000
5V in
+
C1
47uF
GND
1 A Synchronous Switching Regulator SC1409
C3
0.033uF
R1
OPEN
U1
1 SYNC/FSET ISET 8
2 EN/SS
VIN 7
3
AGND
6
PHASE
4 FB
PGND 5
SC1409IS
C6
0.1uF
Place C6 across pins 7 and 5
of SC1409, as close as
possible to package
L1
100uH
Coilcraft
DO3316P-104
R2
1.74k*
C4
OPEN
R3
OPEN
+
C2
47uF
R4
1.0k
C5
OPEN
R5
OPEN
3.3V Out
Typical Application Circuit
COMPONENT SELECTION
Input Capacitor
Soft Start Capacitor
The soft start capacitor value determines the soft start
time according to the following equation:-
The Input capacitor(s) must be capable of 0.5A RMS C = 0.015t
ripple current. Total capacitance values of 22uF to
where C is the soft start capacitor value in uF
47uF are suitable with Esr of less than 350mΩ. Typical and t is the soft start time in mS
capacitors would be AVX TPS Tantalum surface
mount type TPSC476M010R350 or Panasonic Spe- Startup from a shutdown condition will take longer than
cialty Polymer Aluminum Electrolytic surface mount this since the soft start capacitor must charge from its
type ECGC0KB470RA. Other types of capacitor are shutdown value to approximately 1V at a charge cur-
also suitable, such as high value ceramic or Aluminum rent of 1uA before the shutdown is released and true
electrolytics.
soft start begins.
Inductor
Divider Resistors
Suitable Inductor values are in the range of 47uH to The current through the divider chain should be at least
330uH, higher inductor values give lower output volt- 1000 times higher than the FB input bias current to
age ripple and slower transient response time. Inductor eliminate ratio errors. This gives a maximum value for
ripple current acts with the output capacitor ESR to
the bottom divider resistor (R4) of 24kΩ
produce output voltage ripple. For a given output volt- The top resistor (R2) can then be determined from
age ripple requirement, L can be calculated from
R2 = (Vo-1.203)·R4/1.203
( ) L ≥ VIN − VOUT ⋅ ESR ⋅ VOUT
VRIPPLE ⋅ f ⋅ VIN
Compensation
Normally, external compensation is not recommended,
however, if required, loop response can be tailored
Output Capacitor
with suitable values for R3, R5, C4 and C5. Consult the
The output capacitor requirements are similar to the factory for details.
input capacitor except ripple current is lower. Similar
capacitors will be suitable.
© 2000 SEMTECH CORP.
7
652 MITCHELL ROAD NEWBURY PARK CA 91320
Share Link: 