AN701
Vishay Siliconix
Document Number: 70575
16-Jan-01
www.vishay.com
1
Designing High-Frequency DC-to-DC Converters
With the Si9114A Switchmode Controller
C0073C0078C0084C0082C0079C0068C0085C0067C0084C0073C0079C0078
Vishay Siliconix’s Si9100 monolithic switchmode PWM
controller established the standard for low-power, high-
efficiency dc-to-dc converters. This versatile device integrates
a number of useful features, including a power MOSFET,
high-voltage start circuitry, and low power consumption. The
Si9114A controller pushes the limits for high-frequency power
conversion by further reducing delay times and adding
additional features. As a result, dc-to-dc converters can be
designed for frequencies up to 1 MHz with simple PWM
topologies instead of the complex resonant ones.
The Si9114A uses constant frequency current mode control.
By increasing the conversion frequency, power supply
designers will be able to:
C0083 reduce the size of energy storage components
C0083 increase reliability by using ceramic capacitors
C0083 produce an all-surface-mount assembly solution
C0083 lower system costs
C0083 simplify the implementation of a distributed power
architecture.
Traditionally, distributed power has been regarded as costly
and impractical to implement due to the high cost of local
power conversion and the perceived complexity of resonant
power supplies. But these decision criteria are now being
changed by the availability of small-outline control ICs,
LITTLE FOOTC0114 MOSFETs, ceramic capacitors, and new
magnetic components.
Figure 1 Si9114A Block Diagram
R
+
–
–
+
+
–
+
–
+
–
FB COMP
OSC
2 V
Ref
Gen
R
S
Q
1.25 V
Undervoltage
0.2 V
9.2 V
SS
Error
Amplifier
V
CC
+V
IN
R
OSC
C
OSC
4.6 V
20 C0109A
Lockout
V
REF
CURRENT SENSE
–V
IN
DRIVER
OUTPUT
SHUTDOWN
–V
IN
S
Q
NI
V
CC
OSC
Out
Enable
SYNC
+–
+
–
4
3
7
14
1
12
11
2
5 6 13 10 8 9
20 C0109A
Substrate
B 2