JAJSRA2A December 2022 – September 2023 AFE11612-SEP
PRODUCTION DATA
The AFE11612-SEP features twelve 12-bit DACs. The device has an internal 2.5‑V reference that scales the DAC output range from 0 V to 5 V. GaN PAs require negative gate voltage to be properly biased, with pinch-off voltages being more negative than the on voltages. The DAC output can be converted to a negative voltage through the use of a differential op-amp circuit that is powered by a negative power supply (VSS). The following circuit uses the op-amp OPA4H199-SEP to offset and scale the 5-V output range to –7.5 V to 0 V. A differential op-amp circuit is used to protect the PA in case of an alarm shutdown. In an alarm state, the DAC drives the voltage to 0 V. The differential circuit outputs –7.5 V to the GaN gate, making sure that the GaN PA turns off.
The AFE11612-SEP 2.5‑V reference output provides the offset voltage for the differential circuit. The resistors in the circuit were selected with the purpose of providing a –7.5 V to 0 V output range, while not significantly loading VREF. The OPA4H199-SEP has a 40-V supply range, and the circuit can be modified to support greater negative-voltage applications if needed.