AMC7834 Datasheet, PDF (39/93 Pages) Texas Instruments – AMC7834 12-Bit Integrated Power-Amplifier Monitor and Control System with Temperature, Current and Voltage Supervision Capabilities

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AMC7834
SLAS972B – NOVEMBER 2014 – REVISED MARCH 2016
7.3.5 Drain Switch Control
The AMC7834 device includes an output-control voltage (PA_ON pin) capable of driving an external PMOS
switch that turns on and off the drain current to a PA FET. The use of this control signal in conjunction with the
DAC clamp option allows control of the sequence in which the PA FET is powered up and powered down.
The OFF and ON states of the PA_ON signal are equal to the PAV_DD and AGND pins, respectively. The default
state of the PA_ON signal is off (PMOS switch off).
V(DRAIN)
PMOS Switch
PAV_DD
PA_ON
Control
PA_ON
PA Controller
DAC
V(BIAS)
HPA
RF Out
RF In
Figure 53. PA_ON Operation
The maximum output voltage is determined by the PAV_DD pin and limited to a maximum of 20 V. For PA FETs
with drain voltages higher than 20 V, tying the PAV_DD pin to one of the other supply devices (preferably AV_DD)
and scaling the control signal externally is recommended.
The PA_ON signal state can be set through a register write, but it can also be configured to be triggered
automatically by the ALARMOUT pin, any of the SLEEP signals or by the special AV_SS and AV_DD monitoring
circuits.
For FETs requiring a negative bias voltage, such as GaN, ensuring that the bias voltage remains within an
acceptable range is crucial otherwise significant and irreversible damage to the FET can occur. The AMC7834
bipolar DAC operation and clamping mechanism rely on the AV_DD and AV_SS voltages for proper operation. For
this reason, when either the AV_DD or AV_SS voltage falls outside its acceptable range, turning off the drain current
to the FET is desirable.
The AV_DD detection circuit is set to trigger the PA_ON signal to the OFF state in response to an out of range
event. Additionally, the AV_SS detection alarm can be set to trigger the PA_ON signal to the OFF state by setting
the PAON_AVSS bit to 1 in the AMC configuration 1 register (address 0x11). The AV_SS alarm is set by default to
prevent the PA_ON output from entering the ON state (PMOS switch on). In this case writing to the PA_ON
register bit to enable the ON state is ignored. If this additional protection is not needed it can be disabled by
clearing the PAON_AVSS bit.
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