ZNBG3010 datasheet(5/10 Pages) ZETEX

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FUNCTIONAL DIAGRAM

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 ZNBG3010/11 contains 3 such stages. The

negative rail generator is common to both devices.

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 ZNBG3010 this is nominally 2.2 volts

whilst the ZNBG3011 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.

Since the FET is a depletion mode transistor, it is often 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.

ZNBG3010

ZNBG3011

4-118

ZNBG3010 数据表(PDF) 5 Page - Zetex Semiconductors