SC1109 데이터 시트보기 (PDF) - Semtech Corporation
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SC1109 Datasheet PDF : 17 Pages
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SYNCHRONOUS PWM CONTROLLER WITH
DUAL LOW DROPOUT REGULATOR
CONTROLLERS
SC1109
PRELIMINARY - October 16, 2000
LAYOUT GUIDELINES
Careful attention to layout requirements are necessary
for successful implementation of the SC1109 PWM
controller. High currents switching at 200kHz are pre-
sent in the application and their effect on ground plane
voltage differentials must be understood and mini-
mized.
1). The high power parts of the circuit should be laid out
first. A ground plane should be used, the number and
position of ground plane interruptions should be such
as to not unnecessarily compromise ground plane in-
tegrity. Isolated or semi-isolated areas of the ground
plane may be deliberately introduced to constrain
ground currents to particular areas, for example the in-
put capacitor and bottom FET ground.
2). The loop formed by the Input Capacitor(s) (Cin), the
Top FET (Q1) and the Bottom FET (Q2) must be kept
as small as possible. This loop contains all the high cur-
rent, fast transition switching. Connections should be as
wide and as short as possible to minimize loop induc-
tance. Minimizing this loop area will a) reduce EMI, b)
lower ground injection currents, resulting in electrically
“cleaner” grounds for the rest of the system and c) mini-
mize source ringing, resulting in more reliable gate
switching signals.
3). The connection between the junction of Q1, Q2 and
the output inductor should be a wide trace or copper
region. It should be as short as practical. Since this
connection has fast voltage transitions, keeping this
connection short will minimize EMI. Also keep the
Phase connection to the IC short, top FET gate charge
currents flow in this trace.
4) The Output Capacitor(s) (Cout) should be located as
close to the load as possible, fast transient load cur-
5V IN
3.3V IN
12V IN
5V STBY
U4 SC1109CS
VCC
STBY
BCAP+
BST
DH
BCAP- PHASE
SS/EN
PWRGD
DL
VOSENSE GND
GATE2 GATE1
LDOS2 LDOS1
+ C10
330uF
2.5V
+
+
VTT
+
Heavy Lines indicate
high current paths.
1.8V
+
Layout diagram for the SC1109
© 2000 SEMTECH CORP.
13
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