Question about HMC346 Control Input

Hi Kazu,

Unfortunately no, V1 and V2 are not interchangeable. Please refer to the application circuit on the datasheet.

Hello, I have some preamps module made by ar(Amplifier research), the HMC346 found burnt, after replaced this chip.

The output waveform still very low, after compare with the good unit, the key problem is V1 abnormal(gain set to min, this pin is -2.6V, gain set to max, this pin is -1.7v, we can get 18db attenuation), but the defective one we mesured -4V almost no change of V1. Some thing is interesting,  according to the datesheet, the control pin is V1, but you can find the schematic, actuallly the control pin is V2, you said the control pin cannot connect to V2. But this preamp almost match the schematic. So I'm confused.

BTW, I replace a few HMC346, but the defective preamp still cannot fixed.

My understood is, if we change the control voltage of V1, the V2 will also change(this signal control by inside of I signal of HMC346, am I right), hope you can reply me ASAP.

Thank you!

Vic

Hello, I have some preamps module made by ar(Amplifier research), the HMC346 found burnt, after replaced this chip.

The output waveform still very low, after compare with the good unit, the key problem is V1 abnormal(gain set to min, this pin is -2.6V, gain set to max, this pin is -1.7v, we can get 18db attenuation), but the defective one we mesured -4V almost no change of V1. Some thing is interesting,  according to the datesheet, the control pin is V1, but you can find the schematic, actuallly the control pin is V2, you said the control pin cannot connect to V2. But this preamp almost match the schematic. So I'm confused.

BTW, I replace a few HMC346, but the defective preamp still cannot fixed.

My understood is, if we change the control voltage of V1, the V2 will also change(this signal control by inside of I signal of HMC346, am I right), hope you can reply me ASAP.

Thank you!

Vic

HI Vic,

As shown in the typical application circuit attached above, V1 is the control input voltage. The external op-amp circuit maintains the impedance match and provides the rail-to-rail capability, which is +5V to -5V. Moreover, a diode between V2 and I is used to prevent V2 from exceeding 0V.

Based on your description, V1 range is only -2.6V to -1.7V, however, it should be -5V to 0V in order to achieve the full 30dB attenuation range.

Hi Zwang, this design only have 18db attenuation.

Thanks for your reply.