Hello,
I have designed a prototype board for an RF amplifier using the HMC460LC5 together with the HMC981LP3E active bias controller IC, following the guidelines in AN-1363. A part of the schematics is shown below.
It seems like the HMC981LP3E is not working properly since that VGATE is tracking VNEG. Whatever I try to do VGATE is always equal to VNEG.
Changing the Vneg feedback resistor (R4 in my schematics) results in a change of VNEG value, so the internal negative voltage generator seems to work correctly responding well to the feedback.
The datasheet of HMC981LP3E specifies some operation modes in Table 2. By trying to follow Mode1 I removed the R2 and R4 resistors in order to leave VNEGFB (7) and VGATEFB (8) pins floating. The result is that VNEG reaches -2.5V (sounds correct) and VGATE is also following as always.
The Enable (4) pin is connected to an external MCU. When the device is disabled VDRAIN=0V correctly, but VGATE=VNEG. The datasheet states that the operation of VNEG is independent of the EN condition, however EN should control VGATE. Thus when EN is low I'm expecting both VDRAIN and VGATE to turn off.
Some side notes.. All components used to assembly the prototype board are new, supplied from Mouser. Everything is soldered properly. Trying disconnecting VGATE from the load didn't have any impact.
thank you in advance!
Best regards,
Max
