SC4502H Semtech Corporation, SC4502H Datasheet - Page 14

• Manufacturer Part Number: SC4502H
• Description: 1.4 Amp, 2 Mhz Step-up Switching Regulator With Soft-start | Semtech
• Manufacturer: Semtech Corporation

empirically by observing the inductor current and the
output voltage during load transient. Compensation is
optimized when the largest R
producing ringing or excessive overshoot in its inductor
current and output voltage are found. Figures 9(b), 10(c),
11(b) and 11(c) show load transient responses of
empirically optimized DC-DC converters. In a battery-
operated system, compensating for the minimum V
the maximum load step will ensure stable operation over
the entire input voltage range.
C
cases, it improves the transient speed of the converter.
C
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, the size of the loop formed by these
components should be minimized. Since the power switch
is integrated inside the SC4502/SC4502H, grounding
the output filter capacitor next to the SC4502/SC4502H
ground pin minimizes size of the high di/dt current loop.
Figure 9(a). 1.35 MHz All Ceramic Capacitor 3.3V to 12V Boost
Applications Information
POWER MANAGEMENT
Typical Application Circuits
2.2 F
5
6
C1
3.3V
VIN
2005 Semtech Corp.
adds a feedforward zero to the loop response. In some
rolls off the gain at high frequency. This helps to
OFF
47nF
C3
Converter.
ON
10
3
SHDN
SS
IN
GND
5
8
L1: Sumida CR43
4,5
SC4502
and C
5.6 H
L1
ROSC
9
COMP
6,7
6
SW
FB
R4
9.31K
3
are often not needed.
and the smallest C
2
1
10BQ015
R3
40.2K
1.8nF
C4
D1
174K
R1
20K
R2
4
without
12V, 0.3A
VOUT
10 F
C2
IN
and
14
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 the EMI but also decreases the sizes of the
switching voltage spikes and glitches.
Figure 8 shows how various external components are
placed around the SC4502/SC4502H. 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 SC4502/SC4502H
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.
Figure 9(b). Load Transient Response of the Circuit in Figure
Lower Trace : Inductor Current, 0.5A/div
Upper Trace : Output Voltage, AC Coupled, 1V/div
9(a). I
at 1A/ s.
LOAD
is switched between 0.1A and 0.3A
SC4502/SC4502H
40 s/div
www.semtech.com
JA
)