SC4503EVB View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC4503EVB' PDF : 22 Pages View PDF
SC4503
POWER MANAGEMENT
Applications Information (Cont.)
Figures 7(a)-7(c) show the effects of different values of
inductance and feed-forward capacitance on transient re-
sponses. In a battery-operated system if C4 is optimized for
the minimum V and the maximum load step, the converter
IN
will be stable over the entire input voltage range.
VOUT
0.5V/div
IL1
0.5A/div
Board Layout Considerations
In a step-up switching regulator, the output filter capacitor,
the main power switch and the rectifying diode carry pulse
currents with high di/dt. For jitter-free operation, the size of
the loop formed by these components should be minimized.
Since the power switch is integrated inside the SC4503,
grounding the output filter capacitor next to the SC4503
ground pin minimizes size of the high di/dt current loop.
The input bypass capacitors should also be placed close to
the input pins. Shortening the trace at the SW node reduces
the parasitic trace inductance. This not only reduces EMI
but also decreases switching voltage spikes.
40µs/div
(a) L1 = 5.6µH and C4 = 2.2pF
Figure 8 shows how various external components are
placed around the SC4503.
The large surrounding ground plane acts as a heat sink
for the device.
VOUT
0.5V/div
IL1
0.5A/div
40µs/div
(b) L1 = 5.6µH and C4 = 3.3pF
VOUT
0.5V/div
IL1
0.5A/div
VOUT
R1 C4
R2
GND
D1
L1
VIN
C2
FB
SW
U1
JP
C1
R3
C3
SHDN/SS
Figure 8. Suggested PCB Layout for the SC4503.
40µs/div
(c) L1 = 3.3µH and C4 = 2.7pF
Figure 7. Different inductances and feed-forward capaci-
tances affect the load transient responses of the
3.3V to 12V step-up converter in Figure 10(a).
IOUT is switched between 90mA and 280mA.
2007 Semtech Corp.
14
www.semtech.com
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