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Question asked by MikeBAE on May 4, 2017
Latest reply on Sep 5, 2017 by MikeBAE


I'm using a HMC980LP4E to bias a TGA2513SM LNA at 5V, 75mA, (vg ~ -60mV but I measure around -20mV) and although the bias appears stable/correct, the TRGOUT is not active. Only when I touch the VDRAIN, ISENSE or FIXBIAS lines with a multimeter probe does the TRGOUT activate. I suspect the loop is not actually stable or cannot quite reach the state where TRGOUT is activated. This is random across multiple boards. There is no explanation in the data sheets or AN-1363 how TRGOUT is generated, what conditions need to be met etc. Only how to daisy chain ABCs.

The circuit description is as follows:


S0 & S1 are each tied to 0V via 1kohm resistors.

R7 is 324kohm for external VNEG = -1.22V

ALM is not used with ALMH, ISET and ALML tied together with 10kohm to 0V

FIXBIAS resistor is 10kohm

VNEGFB is tied to 0V to disable negative voltage generator

Vdd is +5.3V

VG2_CONT is +3.3V for VG2 = +2V

VG1 has a 2.2uF ceramic, and a 10nF feed-through capacitor.

VDRAIN has just a 10n feed-through capacitor (in hindsight should have more decoupling)

I've tried loading up the VG1 and VDRAIN with additional 4u7 and 1uF capacitors with no change.

Any ideas?