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Document Number: 70004

S11-0975-Rev. I, 16-May-11

Vishay Siliconix

Si9110, Si9111

This document is subject to change without notice.

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.

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

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

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

SHUTDOWN

RESET

Output

H

H

Normal Operation

H

Normal Operation (No Change)

L

H

Off (Not Latched)

L

L

Off (Latched)

L

Off (Latched, No Change)

Figure 6. 5 Watt Power Supply for Telecom Applications

Si9110

GND

FEEDBACK

- 48 V

240 k

390 k

13

14

6

10

1

59

2

8

7

4

3

150 k

3 k

100 pF

2N7004

18 k

12 k

1N5822

1N5819

1N4148

20 µF

0.1 µF

0.022 µF

0.1 µF

1 µF

220 µF

47 µF

OSC SYNC PULSE

(If Needed)

+ 5 V

at 0.75 A

- 5 V

at 0.25 A

Feedback

To Pin 14

1

Ω