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THS4502: What is the range of Vocm of this part

Venkatesh P17
Intellectual 895 points
Part Number: THS4502
Other Parts Discussed in Thread: ADS8900B, THS4551, , THS4500

Hi TI Team, 

Can you please help me to understand the range of Vocm pin of this part?

Because I am using the ADC ADS8900B  with Vref=2.5V so the ADC input common-mode voltage should be Vref/2=1.25V. 

Previously I used THS4551 But My input voltage points are from a 6V rail, so THS4551 cannot afford this much voltage in input because its Vcc is just 5V.

So I have chosen this part [THS4502] with 12V as Vcc. My doubt is whether I can able to configure the THS4502 in 1.2V? [Vocm=1.2V]

Please reply regarding this,

Thanks and Regards,

  • 0
    Guru 140200 points
    Hi Venkatesh,

    can you post a schematic?

    Kai
  • 0 in reply to kai klaas69
    Intellectual 895 points

    Hi Kai
    Here is my schematic in simple form. I can share this in Tina or ORCAD file in office hour. But now I just drew it in notebook.

    Thanks and Regards,

  • 0
    TI__Genius 15565 points
    Hello Venkatesh,

    For a 12V single supply for the THS4502, your VOCM input range should be between 1V to 11V.

    Best,
    Hasan Babiker
  • 0 in reply to Hasan Babiker31
    TI__Genius 15565 points

    It is also worth noting that while 1.2V meets the input range of the Vocm pin, you will be limiting the output range of your device. Each of the output pins of the device (Vout+ and Vout-) can swing within approximately 1v from either rail (1V to 11V in this case). You will need to be sure that either output pin does not saturate and ruin the overall differential output. You will notice this means you cannot exceed a differential output greater than around 400mV. For a Vocm level of 1.2V I would suggest using the device in a dual supply configuration in order to significantly increase the output range of your amplifier.

    - Hasan Babiker

  • 0 in reply to Hasan Babiker31
    Intellectual 895 points

    Hi Hasan Babiker31,

    Thanks for the reply.

    I will try and verify this in Tina with your comments and let you know.

    Can you please suggest the design suitable for ADS8900B with Vref=2.5V using this THS4502?

    And Digikey says this THS4502 is obsolete. So can I use  THS4500?

    Thanks and regards,

  • 0 in reply to Venkatesh P17
    Guru 140200 points
    Hi Venkatesh,

    www.ti.com/.../samplebuy

    Can you show your schematic? What have you done with the THS4502 so far?

    Kai
  • 0 in reply to kai klaas69
    TI__Genius 15565 points
    Hey Venkkatesh,

    Were you able to perform a TINA analysis? Can you provide the schematic? What is the range of your input differential signal? You can follow the link Kai provided to buy THS4502 parts.

    Best,
    Hasan Babiker
  • 0 in reply to Hasan Babiker31
    Intellectual 895 points

    Hi Hasan Babiker31,

    I went to the link given by Kai but in TI-store the part is already sold, Not available.

    I visited the websites Mouser and Digikey, they also shows the message as non stock and Obsolete.

     

    we don't need a obsolete part or the part will go obsolete in recent few months. So please suggest me a good long life part in this family. I thought to use THS4500IDGKR Is this will have long day availability?

    i hope this is closely same as THS4502, am right? If no please guide me to choose right one.

    Thanks and Regards,

  • 0 in reply to Hasan Babiker31
    Intellectual 895 points

    Hi Hasan Babiker31,

    I thought to use THS4500, Because at initial, we may buy just 100units, but in future we need the part to be available. So I think THS4500 is good enough. Please confirm the same.

    Here I attached the basic circuit.left side.TSC

    I thought to reduce the sense resistor value so the gain of the THS4500 amp should be increased. Is it possible to configure the gain of THS4500 to 10V/V [Sense resistor value reduction as 10times say 50mOhm] using 100Ohm at inputs and 1K at feedback's? is there any limitation?

    If I change the sense resistor from 500mOhm to 50mOhm, can I get the step of each 10uA? my current measurement range is upto 5A with 10uA resolution. I am going to use ADS8900B as my ADC.

    I asked help to Keith Nicholas [TI employee] for my design, He guiding me form so far. 

    Please refer the circuit and suggest If i have to change anything

    Thanks and Regards,

  • 0 in reply to Venkatesh P17
    Guru 140200 points

    And click on the blue arrow.

    From which country do you want to order the THD4502?

    Kai

  • 0 in reply to Venkatesh P17
    TI__Genius 15565 points

    Hello Venkatesh,

    I have a few comments regarding this design:

    1) As Kai has highlighted, the THS4502 is not an obsolete device. However like you have shown there are no samples available for this device. The "obsolete" comment on digikey is in regards to that specific DGKR package type but there are many other types available as can be seen in the TI store. Regardless, the THS4500 can also be used.

    2) Again I would recommend using a dual supply configuration of +/- 6V. As you can see from the TINA simulation you provided, OUT- (VF4) is being driven very close to the negative supply rail (GND) but would actually rail somewhere around 1V in a real case scenario. After experimenting with the model, I found that the THS4500 was able to supply a negative output even when VEE was set to 0V. The model only seems to perform normally under a dual supply configuration. I will look into either getting the model updated or at least putting this information in the MACRO notes.

    3) I would not recommend using a gain configuration of 10V/V for your design. If you change the configuration to a dual supply of +/- 6V, having VF6 and VF7 around 4.26V will meet your input common mode range requirments. The input common mode range should be around +/-5V in this case. You will see that changing R3 to 50mOhms and lowering R5 and R6 to 100Ohms, will allow you to exceed the input common mode range, giving you a non-linear output.

    Best,

    Hasan Babiker