HMC980_12 Datasheet, PDF (15/20 Pages) Hittite Microwave Corporation – Active Bias Controller

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Over current
Set current
Under current
HMC980
Active Bias Controller
High Current
ALARM
Figure 1. Current Alarm Behavior
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.
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