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Phone: 978-250-3343

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Application Support: Phone: 978-250-3343 or apps@hittite.com

15

HMC980

v00.0312

Active BiAs controller

High current

Power-up and enable sequencing

to ensure the safety of the external amplifier, the hMC980 provides an automatic power-up sequence for enabling the

active bias control loop. During start-up VDrain and VG2 are kept at GnD while VGate is taken to the most nega-

tive supply available (VGate=VneG). this ensures that external amplifier is completely pinched-off before VDrain

is applied. When en signal is received, VDrain is applied and the active bias loop is enabled. after the VDrain

is applied, VG2 is generated. the power-up sequence is completed by increasing the VGate linearly until the set

iDrain value is reached.

For power-down and disabling, the same sequencing is applied in the reverse order.

Daisy-chain operation

hMC980 produces a trigger out signal (triGoUt pad#19) when the quiscent current is in regulation. this trigger

signal can be used to enable additional hMC980 chips in a chain of amplifiers. the triggering sequence can be routed

in any way, from input to output, or from output to input depending on the use. Figure-2 shows a sample use of three

hMC980s in an amplification chain. please note that, only one of the hMC980 (in master mode) is used to generate

the negative voltage and the remaining hMC980 (in slave mode) is set to receive external negative voltage (which is

provided from the master depletion mode hMC980). Generating negative voltage from a single hMC980 reduces the

number of the components in the system, and decreases the over all current consumption.

please note that, to ensure proper start-up, the system enable signal should be applied to the depletion master mode

device that has the negative voltage generator.

Over current

Set current

Under current

ALARM

Figure 1. Current Alarm Behavior