ZNBG2000 datasheet(4/7 Pages) DIODES

4 / 7 page

FUNCTIONAL

DESCRIPTION

The ZNBG devices provide all the bias requirements

for external FETs, including the generation of the

negative supply required for gate biasing, from the

single supply voltage.

The diagram above shows a single stage from the

ZNBG series. The ZNBG2000/1 contains 2 such

stages.

The drain voltage of the external FET QN is set by the

ZNBG device to its normal operating voltage. This is

determined by the on board VD Set reference, for the

ZNBG2000 this is nominally 2.2 volts whilst the

ZNBG2001 provides nominally 2 volts.

The drain current taken by the FET is monitored by

the low value resistor ID Sense. The amplifier driving

the gate of the FET adjusts the gate voltage of QN so

that the drain current taken matches the current

called for by an external resistor RCAL. Both ZNBG

devices have the facility to program different drain

currents into selected FETs.

Since the FET is a depletion mode transistor, it is

usually necessary to drive its gate negative with

respect to ground to obtain the required drain

current. To provide this capability powered from a

single positive supply, the device includes a low

current negative supply generator. This generator

uses an internal oscillator and two external

capacitors, CNB and CSUB.

ISSUE 1 - AUGUST 2001

ZNBG2000

ZNBG2001

FUNCTIONAL DIAGRAM

ZNBG2000 Datasheet(PDF) 4 Page - Diodes Incorporated