Si9122

Vishay Siliconix

www.vishay.com

2

Document Number: 71815

S-41944—Rev. F, 18-Oct-04

TECHNICAL DESCRIPTION

Si9122 is a voltage mode controller for the half-bridge

topology. With 100-V depletion mode MOSFET capability, the

Si9122 is capable of powering directly from the high voltage

powered through an external regulator directly through the

throughout the entire line and load range. In order to simplify

the traditional secondary synchronous rectification, Si9122

provides intelligent gate drive signals to control the secondary

MOSFETs. With independent gate drive signals from the

controller, transformer design is no longer limited by the gate

to a source rating of the MOSFETs. Si9122 provides constant

charge loss as well as conduction loss. A break-before-make

function is included to prevent shoot through current or

transformer shorting. Adjustable Break-Before-Make time is

incorporated into the IC and is programmable by an external

resistor value.

Si9122 is packaged in TSSOP-20 and MLP65-20 packages.

In TSSOP-20 packaging, both standard and lead (Pb)-free

options are available. The MLP65-20 package is

lead (Pb)-free.

In order to satisfy the stringent ambient

temperature requirements, Si9122 is rated to handle the

industrial temperature range of –40 to 85_C. When a situation

arises which results in a rapid increase in primary (or

secondary current) such as output shorted or start-up with a

large output capacitor, control of the PWM generator is handed

over to the the current loop. Monitoring of the load current is

by means of a sense resistor on the primary low-side switch.

DETAILED BLOCK DIAGRAM

−

+

Pre-Regulator

−

+

−

+

REG_COMP

+

−

Error Amplifier

132 kW

EP

−

+

PWM

Comparator

SS

−

+

CS2

CS1

Over Current Protection

GND

Duty Cycle

Control

Driver

Control

and

Timing

BBM

OTP

OSC

Ramp

PGND

SYNC

Driver Low

SYNC

Driver High

Low-Side

Driver

High-Side

Primary

Driver

Int

BST

Si9122

Peak DET

Figure 2.

VREF

2

60 kW

8.8 V

550 mV

20 mA

8 V

9.1 V