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TPS6594-Q1: Feedback network sampling method

Part Number: TPS6594-Q1

Hi Team

For PMICs, the sampling method of the BUCK circuit includes differential sampling and single-ended sampling. Are there any advantages or disadvantages of these two methods? Or which method is generally used?

In addition, some of the sampling feedback networks are direct output voltage sampling, while others use remote input (power supply IC) input sampling. And in the manner of differential sampling. Can use single-ended sampling in this case? Thanks.

Best regards,

Ansel Song

  • Hi, Ansel,

      The differential sampling can cancel common mode noise but needs 2 pins; single-ended sampling can't cancel common mode noise but needs 1 pins.

      The TPS6594-Q1 device has only one pin for single-ended sampling when it's configured as single-phase; when any multiple phase is configured, and then differential sampling is used by using the other rail's feedback pin as FBN. 

      Please follow TI's reference design for all bucks phase configuration. 

  • Hi Phil,

    In some PMICs, such as Qualcomm, some sampling is differential remote-voltage sensing.

    Can  use single-ended differential sampling for remote sampling? 

    Best regards, 

    Ansel Song

  • Hi, Ansel,

       It depends on how solid the return path is. If the device has 2 pins for differential remote-voltage sensing, it's better to use them as they're designed. 

  • Hi Phil,

    So for remote sampling, is differential sampling better than single-ended sampling?  

    Is there comparison analysis for remote sampling, differential and single-ended sampling?  Thanks.

    Best regards,

    Ansel Song

  •   Yes, from performance point of view, differential sampling better than single-ended sampling. 

      I have no existing data for their comparison analysis, but I can tell you more details about their difference below:

      A signal input circuit where SIGNAL LO and SIGNAL HI are electrically floating with respect to ANALOG GROUND. For example, a differential input A/D card will have one HI (+) and one LOW (-) pin for each input.

     There will also be a LLGND (LOW LEVEL GROUND) pin which may be used if a ground connection is required. This allows the measurement of the voltage difference between two signals tied to the same ground and provides superior common-mode noise rejection.

    2. Where should differential signal inputs be used?

    Whenever electromagnetic interference (EMI) or radio frequency interference (RFI) is present, a voltage can be induced on BOTH signal wires.
    A differential input amplifier will reject the COMMON MODE VOLTAGE, provided that the common mode voltage plus the input signal does not exceed the device's CMR specification. The effect on a single-ended input is usually a voltage fluctuation between signal high and signal ground.

    3. Single-ended inputs

    A single signals input has no commond mode range because there is only ONE low wire, which is shared by all inputs.

    For example, if you have an A/D board with 16 single-ended inputs, there will be 16 HIGH (+) lines and one LOW (-) line (sometimes called LLGND). Some cards may have several LOW lines to provide extra places to make your ground connection, however, these lines are tied together and are basically the same thing.

    4. When to use single-ended or Differential signals?

    Differential inputs provide a more stable reading when EMI or RFI is present, and therefore, it is recommended to use them whenever noise is generally a problem. This is especially true when measuring thermocouple, strain gage and bridge type pressure sensor inputs, since they produce very small signals that are very succeptible to noise. Single-ended inputs are lower in cost, and provide twice the number of inputs for the same size wiring connector, since they require only one analog HIGH (+) input per channel and one LLGND (-) shared by all inputs. Differential signals require signal HIGH and LOW inputs for each channel and one common shared LLGND. Single-ended inputs save connector space, cost, and are easier to install.

  • Hi Phil,

    Thanks very much for your reply, it is very clear.

    Best regards,

    Ansel