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Power supply for instrumentation amplifier

Tim H
Prodigy 20 points
Other Parts Discussed in Thread: INA122, TPS61080, TPS65130, TPS61040

Hi,

I am designing an ECG amplifier circuit using, for example, the INA122 (single supply).

Ive found a lot of information about amplifiers and filtering but finding info on a suitable power supply is a bit harder.

The device will be powered by a single cell Li-Ion battery.

My current line of thinking is using a something like the TPS61080DRC at 600kHz boosting the batt voltage to say 6V, then linear regs to take it down to +5V (TPS71701DCK) and +2.5V (TPS79901DDC).

Another alternative ive come up with is using a charge pump doubler and a charge inverter with a couple of lin regs to get +5V and -5V but the output impedance of these devices coupled with having decent headroom for the lin regs meant that this method was a headache...

Can anyone give me any advice on this? Im sure it's a very common problem.

Thanks,

Tim

  • 0
    TI__Intellectual 1955 points

    Hi Jeff,

    The INA122 has a wide input range.  Based on your question, it appears that you are considering two different ways to power it.  If you can narrow it down, then we can help design the supply.  If you are asking what is the best way to power the INA122 itself, let me know. 

    I suspect that the best way is similar in concept to what you already proposed, i.e. a boost converter followed by a linear regulator to clean up the ripple.  The TPS61080 is not the best choice for boost to such a low voltage.  If you want to go dual supply, then the TPS6513x family can provide the dual rails.

    Please let me know if this helps.

    Regards,

    nancy!

  • 0 in reply to nancy!
    Prodigy 20 points

    Hi Nancy,

    Thank-you for responding so quickly.

    I've done a lot of thinking about this since my last post and found that this application must have a dual supply.

    Ideally the we would have +5V and -5V of clean power supply from a battery (batt 3.0V -> 4.2V) to power the INA122.

    Would you still recommend the TPS6512x?

    Thanks,

    Tim

     

  • 0 in reply to Tim H
    TI__Intellectual 1955 points

    Tim,

    Depending on your exact range needs, you have the following options for a +6V/-6V boosted/inverted voltages:
     
    TPS6104x + charge pump - Io < 50mA - low cost - see figure 19 in the datasheet.
     
    TPS65130 - Io > 50mA range
     
    followed by TPS717xx to 5V and TPS72301 to get -5V. 
     
    Note that the TPS65130 switches at a much higher frequency than the TPS61040 and so the linear regulators will not be as effective removing the TPS65130's higher switching frequency noise.

    Thanks!

    nancy

  • 0
    Prodigy 15 points

    Hello,

    I have designed an ECG Amplifier using INA 128. But supply seems to be a problem for me. Using an IC number 7660, i was able to generate a negative voltage. But after sometime, ripples were visible in my ECG.

    I'll post m requirement in a simple way.

    From a 3.6 Volts Li battery, please help me to generate a 5 Volts positive and 5 Volts negative Voltage to supply to my Instrumentation amplifier and also to my micro-controller for A to D conversion and wireless transfer.

    Thanks,

    aB..

     

  • 0 in reply to Abhinav null
    Prodigy 10 points

    Hi,

    This requires experimentation, but have you considered filtering the power supply rails by using ferrite beads and capacitors. You can also use common mode inductor wit 2x capacitors.

    Careful PCB layout and shielding some parts of your PCB may also help.

    Regards,

    Dimo