ADL5391 used as low frequency multiplier


I decided to test the ADL5391 to multiply two 50 kHz signals phase shifted (power measurement).

Line XPLS and YPLS and output WPLS are used, a 100nF DC blocking capacitor is used at X-Y PLS input. Before the DC blocking capacitors, the AC signals is  DC offset by 1.65V (this is correct, it depends on my above circuitry), the AC component is less than 2Vpp. After the DC blocking capacitors, the signal are 2.5V DC offset (midsupply of ADL5391),

XMNS, YMNS and WMNS are connected to the GND through a 100nF capacitor (is that correct?).  PLS and MNS are connected with 56 Ohms resistors

GADJ is left open

VMID is connected with 100 nF to GND.

Z PLS and MNS are left open

The system draws about 30 mA under 5V in Standby. As I enabled the IC, it draws about 250 mA. This seems not normal ! The output WPLS stay to 0V.

Has somebody already used this IC at low frequency in a multiplier configuration ?

What about the MNS inputs/outputs, should I connect it as mentionned above (through 100nF capacitor as in the evaluation board schematics) ?

Thanks for your inputs !

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  • Application is piezo actuator control. signals to be measured are :

    - Load AC voltage and AC current to detect zero-crossing and then perform phase computation. I used the AD8210 current monitor and AD8361 difference amplifier with a controller (comparator). Both AC signal are DC offset by mid supply level.

    - Load RMS voltage and current. The AC signals are "rectified" with a RMS to DC converter AD8361 and then measured with a controller (for both voltage and current).

    These feedback circuits work well. But I also need to perform a load active power measurement, this means :

    - active power measurement : Load AC voltage and AC current have to be multiply, those are not in phase. This will lead to AC power (active) which has to be rectify for instance with a RMS to DC converter.

    Power could be estimated with Urms x Irms x cos (phase) but this is not precise enough. I plan to test a Linear technology IC, the LT2940. This should works at 50 kHz.

    Let me know if you have any comments.

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