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OPA1632: +/-5v power for 6Vpp AC signal

ben biles
Intellectual 840 points
Part Number: OPA1632
Other Parts Discussed in Thread: PGA2500, OPA2134, THP210, THS4561

Hi,

I would like to use 8 x OPA1632's in my 8 channel preamp design with OPA143 's to buffer VQ ( VCOM ) from 8 channel ADC.

looking at typical application design in the datasheet it says "Power supplies as low as ±8 V can be used in this application with excellent performance"

I would like to power the device with ±5 V with input signal coming from PGA2500

input = 8.2Vpp  ( -4.1v to +4.1v) on the input

output = 6Vpp ( -3 V to + 3 V )

with +2.5 V bias on VCOM for the output of between  - 0.5 V to 5.5 V 

Can you tell me if +/-5V power would work in the situation ?

the part says it can run down to +/-2.5V but i'm not sure how much head room is required for given voltage swing.

If not  , can you recommend a TI part that would be good for this ADC buffer in the +/-5v power range?

I'm looking at reducing the gain by around 25% which is the same as the example although I will need to add some

filtering to the design. 

Sorry if this is obvious and detailed in the datasheet and i've overlooked it! 

 

  • 0
    TI__Genius 15555 points

    Hello Ben,

    Headroom at the output is shown here for each output pin:

    For a 6Vpp output signal at 2.5V Vocm, each outpin will vary between 4V &1V. For a +/- 5V supply you are exceeding the headroom limitations even with a 2k-ohm load.

    Which ADC are you driving here? What are your required FDA specs (bandwidth, power, noise, etc.)

    Best,

    Hasan Babiker

  • 0 in reply to Hasan Babiker31
    Intellectual 840 points

    Hi, thanks for your reply Hasan,

    I am using CS5368

    40 kHz bandwidth unweighted 108db  ( measured from 10hz to 20khz  )

    Input Impedance (Differential)  250k

    Full-scale Input Voltage @ maximum 1.24*VA Vpp = 6.2V

    Dynamic Range A-weighted 114db

    I'm not sure what you mean by power specs? I am using the same +/-5v PGA2500 is using.  

    I do have +/-9v elsewhere in the system , but routing that to the 8 preamp cards is a pain just for an ADC buffer.

    the ADC is running on the +5V rail the PGA2500's are using.

    I need super low noise as to not add any noise the PGA2500's nice clean output

    and it would be great to use a differential buffer to keep the space down on the cards.

    I should implement a N X 6.144 MHz) filter according to the DS..

    I need to bias the buffer with approx 2.6v from ADC from its buffered VCOM.

    I will add will probably add decoupling caps between PGA2500 and buffer so PGA can swing around 0v

    How about OPA2134?

    any ideas would be greatly appreciated :) 

  • 0 in reply to ben biles
    TI__Genius 15555 points

    Hello Ben,

    Does the THP210 meet your specifications? If a higher speed device is needed you can also look into the THS4561.

    Best,

    Hasan Babiker