2.12.9 Low Supply Voltage Configuration

The low supply voltage configuration is used when 3.0 V to 5.5 V supply rails are available. All product options of the Si8281 and

Si8283 are intended for this configuration.

An advantage of Si828x devices over other converters that use this same topology is that the output voltage is sensed on the secon-

dary side without requiring additional optocouplers and support circuitry to bias those optocouplers. This allows the dc-dc to operate

with superior line and load regulation while reducing external components and increasing lifetime reliability.

In a typical isolated gate driver application, the dc-dc powers the Si8281 and Si8283 VDDB and VSSB as shown in the figure below.

dary windings, S1 and S2, splits the output voltage into two portions. The positive VDDB and the negative VSSB with common refer-

ence to VMID (IGBT Emitter).

VDDB = VOUT ×

VSSB = − VOUT ×

Type 1 loop compensation made by RCOMP and CCOMP are required at the COMP pin. The combination of RCOMP = 200 kΩ and

CCOMP = 1 nF satisfies most Si8281 and Si8283 dc-dc applications. Though it is not necessary for normal operation, we recommend

that an RC snubber (not shown) be placed in parallel with the secondary winding to minimize radiated emissions.

RDY

/FLT

VH

VL

Si8281/Si8283

Freq. Control

and Shutdown

Soft Start

UVLO

Power

FET

DC-DC

Controller

VSW

SH_FC

SS

VDDA

CSS

RFSW

Power

FET

Error Amp

and

Compensation

Encoder

UVLO

VDDB

VSNS

COMP

VSSB

VSSB

Vin

HF RX

HF TX

RCOMP CCOMP

DSAT

Detection

HF RX

Driver

Miller

Clamp

CLMP

DSAT

VMID

HF TX

Decoder

Encoder

Decoder

/RST

+IN

-IN

Input

Control &

Reset

VDDP

S1

S2

VMID

Figure 2.5. Si8281/83 Block Diagram: 3 V–5 V Input to Split Voltage Output

2.12.10 High Supply Voltage Configuration

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Si8281/82/83/84 Data Sheet

System Overview

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