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13 - 8

13

Pad Number

Function

Description

Interface Schematic

14

TRGOUT

Trigger out signal. Generates a HIGH (3.5V) signal when

the active bias system stabilizes. This signal can be

used to trigger next device (ENABLE) if more than one

HMC981 is used in a daisy chain.

16, 17

VDRAIN

Drain voltage. Should be connected to the supply

terminal of the external amplifier. A minimum 100 nF

capacitor has to be placed close to the external amplifier to

improve load regulation.

18

VGATE

Gate Control pad for external amplifier. Connect to the gate

(base) of the external amplifier. In order to guarantee

stability,a 10μF capacitor should be connected between

the gate (base) terminal of the external amplifier and GND

as close to the amplifier as possible.

21

VNEG

Negative input to the chip. Should be supplied with CPOUT

when negative voltage generator is enabled, or connect to

external VSS when negative voltage generator is enabled.

For detailed usage please refer to the “Negative Voltage

Generator” section.

22

VNEGFB

Feedback (Control) pad for Negative Voltage Generator

Charge Pump. Float to activate the negative voltage

generator / Sort to GND to disable the negative voltage

generator.

24

VGATEFB

Control pad for VGATEFB. Float VGATEFB when a

depletion mode transistor is biased. Selects the mode of

operation along with VNEGFB pad. For detailed usage

please refer to the Table 2.

27, 28

CPOUT

Negative voltage generator charge pump output. Negative

voltage generator needs a flying capacitor, a reservoir

capacitor and two diodes to operate. Please refer to the

application schematic for more info.

HMC981

v00.0611

ACTIVE BIAS CONTROLLER