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THS4531: VOCM voltage divider

Part Number: THS4531
Other Parts Discussed in Thread: THS4532,


I'm planing to use the THS4531 with reduced output common mode voltage. For that purpose I connect a pull down resistor to the VOCM-pin.

I tried this for the THS4532 which in principle should behave the same as the THS4531 - am I right?

When comparing the datasheets of THS4531 and THS4532, I find differet values for the internal VOCM voltage divider :

60k (THS4531, page 33) vs 625k (THS4532, page 26)

These values differ a lot from each other and are even different to that in the electrical characteristics section which gives an input impedance 100k @ 2.7 / 100k @5V at the VOCM pin.

Thus I did some measurements on the THS4532 @3.3V / 2.75V, which gave me approximately 440k resistance of the two voltage divider resistors or equivalent 220k input resistance on the VOCM pin.

Could you please confirm this value (also for the THS4531).

How stable is this value over different samples and temperature?

Thanks in advance and best regards,

Guenther Mader

  • Well Guenther,

    It is likely the THS4531 number is incorrect. There was a very slight build flow change to create the THS4531A where that data sheet shows 625kohm R's for the Vcm setup to midscale, 

    So 400kohm you measured is probably right for the THS4532. There will be quite a bit of variability so if you need any kind of output Vocm accuracy, you should develop that level in external R divider and buffer to the Vocm pins.