SI9110_11 Datasheet, PDF (6/9 Pages) Vishay Siliconix – High-Voltage Switchmode Controllers

Si9110, Si9111
Vishay Siliconix
DETAILED DESCRIPTION (CONT’D)
Oscillator Section
The oscillator consists of a ring of CMOS inverters,
capacitors, and a capacitor discharge switch. Frequency is
set by an external resistor between the OSC IN and OSC
OUT pins. (See Figure 5 for details of resistor value vs.
frequency.) The DISCHARGE pin should be tied to - V_IN for
normal internal oscillator operation. A frequency divider in
the logic section limits switch duty cycle to  50 % by locking
the switching frequency to one half of the oscillator
frequency.
Remote synchronization is accomplished by capacitive
coupling of a positive SYNC pulse into the OSC IN (pin 8)
terminal. For a 5 V pulse amplitude and 0.5 µs pulse width,
typical values would be 100 pF in series with 3 k to pin 8.
SHUTDOWN and RESET
SHUTDOWN (pin 11) and RESET (pin 12) are intended for
overriding the output MOSFET switch via external control
logic. The two inputs are fed through a latch preceding the
output switch. Depending on the logic state of RESET,
SHUTDOWN can be either a latched or unlatched input. The
output is off whenever SHUTDOWN is low. By
simultaneously having SHUTDOWN and RESET low, the
latch is set and SHUTDOWN has no effect until RESET goes
high. The truth table for these inputs is given in Table 1.
Table 1. Truth Table for the SHUTDOWN and RESET Pins
SHUTDOWN
H
H
L
L
RESET
H
H
L
L
Output
Normal Operation
Normal Operation (No Change)
Off (Not Latched)
Off (Latched)
Off (Latched, No Change)
Both pins have internal current source pull-ups and should
be left disconnected when not in use. An added feature of the
current sources is the ability to connect a capacitor and an
open-collector driver to the SHUTDOWN or RESET pins to
provide variable shutdown time.
Output Driver
The push-pull driver output has a typical on-resistance of
20  . Maximum switching times are specified at 75 ns for a
500 pF load. This is sufficient to directly drive MOSFETs
such as the 2N7004, 2N7005, IRFD120 and IRFD220.
Larger devices can be driven, but switching times will be
longer, resulting in higher switching losses. In order to drive
large MOSPOWER devices, it is necessary to use an
external driver IC, such as the Vishay Siliconix D469A. The
D469A can switch very large devices such as the
SMM20N50 (500 V, 0.3 ) in approximately 100 ns.
APPLICATIONS
GND
OSC SYNC PULSE
(If Needed)
1N5822
+5V
at 0.75 A
220 µF
0.1 µF
- 48 V
20 µF
FEEDBACK
V_CC
0.022 µF
13
240 k ₁₄
6
10
0.1 µF
1
390 k
2
Si9110
3k
100 pF
8
150 k
7
4
3
2N7004
5
9
1Ω
1_{/2 W}
1N5819
1N4148
1 µF
47 µF
-5V
at 0.25 A
To Pin 6 V_CC
18 k
Feedback
To Pin 14
12 k
Figure 6. 5 Watt Power Supply for Telecom Applications
Vishay Siliconix maintains worldwide manufacturing capability. Products may be manufactured at one of several qualified locations. Reliability data for Silicon
Technology and Package Reliability represent a composite of all qualified locations. For related documents such as package/tape drawings, part marking, and
reliability data, see www.vishay.com/ppg?70004.
www.vishay.com
Document Number: 70004
6
S11-0975-Rev. I, 16-May-11
This document is subject to change without notice.
THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000