SC4501 Semtech Corporation, SC4501 Datasheet - Page 15

• Manufacturer Part Number: SC4501
• Description: 2MHz Step-Up Switching Regulator
• Manufacturer: Semtech Corporation

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Figure 10(a). 1.35 MHz All Ceramic Capacitor 3.3V to 12V Boost
frequency. However it reduces the phase margin. The
values of R
observing the inductor current and the output voltage
during load transient. Compensation is optimized when
the largest R
ringing or excessive overshoot in its inductor current and
output voltage are found. Figures 10(b), 11(c), 12(b) and
12(c) show load transient responses of empirically
optimized DC-DC converters. In a battery-operated
system, compensating for the minimum V
maximum load step will ensure stable operation over the
entire input voltage range.
C
cases it improves the transient speed of the converter. C
rolls off the gain at high frequency. This helps to stabilize
the loop. C
Board Layout Considerations
In a step-up switching regulator, the output filter capacitor,
the main power switch and the rectifying diode carry
switched currents with high di/dt. For jitter-free operation,
Application Information
POWER MANAGEMENT
Typical Application Circuits
2.2 F
C1
3.3V
5
VIN
2005 Semtech Corp.
adds a feedforward zero to the loop response. In some
OFF
47nF
C3
5
Converter. Pinout Shown is for MSOP-8
ON
3
and C
L1: Cooper-Bussmann SD25-3R3
and C
3
8
3
and the smallest C
6
SHDN
SS
IN
are often not needed.
GND
6
4
4
SC4501
can be determined empirically by
3.3 H
L1
ROSC
7
COMP
5
SW
R4
9.31K
FB
2
1
10BQ015
R3
22.1K
1.5nF
C4
D1
4
without producing
174K
R1
20K
R2
IN
and the
12V, 0.4A
VOUT
10 F
C2
6
15
Figure 10(b). Load Transient Response of the Circuit in Figure
the size of the loop formed by these components should
be minimized. Since the power switch is integrated inside
the SC4501, grounding the output filter capacitor next to
the SC4501 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 the sizes of the
switching voltage spikes and glitches.
Figure 9 shows how various external components are placed
around the SC4501. The frequency-setting resistor should
be placed near the ROSC pin with a short ground trace
on the PC board. These precautions reduce switching
noise pickup at the ROSC pin.
To achieve a junction to ambient thermal resistance (
of 40°C/W, the exposed pad of the SC4501 should be
properly soldered to a large ground plane. Use only 12mil
diameter vias in the ground plane if necessary. Avoid using
larger vias under the device. Molten solder may seep
through large vias during reflow, resulting in poor adhesion,
poor thermal conductivity and low reliability.
Lower Trace : Inductor Current, 0.5A/div
Upper Trace : Output Voltage, AC Coupled, 1V/div
10(a). I
1A/ s.
LOAD
is switched between 0.1A and 0.4A at
40 s/div
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SC4501
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