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TLV700XX-Q1: Question about symmetric power supply regulation

Roberto Duralde
Prodigy 120 points
Part Number: TLV700XX-Q1
Other Parts Discussed in Thread: TPS60403, TPS723-Q1, TLV700, TPS7A39, TPS7A39EVM-865

Hi, I'm sorry to be the one asking the "would this work..." question, but I prefer to ask before buying! So, my question is the following:

If I had one 3.7V Li-ion battery and I needed a symmetric supply for a 3.3V EMG application, could I use a TLV70033-Q1 to regulate it from 3.7V to 3.3V operating at 50mA? By reading the datasheet it seems that it'd work. I'm more confused about the negative part. The negative suuply is working at around 10mA, as it's not supplying the digital circuitry, just the analog, thus I thought about using the TPS60403 60mA Charge Pump Voltage Inverter to get -3.7V, and then use a negative LDO to get -3.3V? (I couldn't find a fixed 3.3V negative voltage regulator that's like the TLV70033-Q1, which would you recommend?)

Would you recommend this setup for EMG applications in which the signals are very susceptible to noise? Maybe the Charge Pump adds too much noise and it's better to get two 3.7 batteries and connect them in series to get the symmetric supply? I hope you understand my questions!

Thanks in advance!

Roberto

  • 0
    TI__Guru 55940 points
    Hi Roberto,

    I notice that you are using the automotive version of the TLV700 for your positive LDO. Does this mean that you need an automotive qualified negative LDO as well? TPS723-Q1 is currently the only negative LDO that is automotive qualified. As you mentioned, you will need to use the adjustable output version in order to achieve a -3.3 V rail.

    If you do not require an automotive grade device, please consider TPS7A39 which is a dual LDO that can provide both your positive and negative output rails. You will still need to provide a negative input for the negative rail.

    The LDO PSRR will reduce the noise from the charge pump and additional passive filtering can be done to further reduce the noise. Ultimately you will need to decide if the reduction will be enough for your application. You can use the TPS7A39EVM-865 as a tool early in your prototyping to help make this determination.

    While I am unaware of a TI Design that is for a EMG application, it sounds like you are looking for a portable solution. You may find inspirations from the power tree of the following reference design for wearable fitness and activity monitoring:

    www.ti.com/.../fitness-activity-monitors

    Very Respectfully,
    Ryan
  • 0 in reply to Ryan Eslinger
    Prodigy 120 points
    The TPS7A39 is a good option actually! And the reference design is pretty interesting too, I'll have a look. Thanks!!