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UCC25800-Q1: ISO power supply for AFE, ADC and digital

MIrtcho Maglijanov
Prodigy 140 points
Part Number: UCC25800-Q1
Other Parts Discussed in Thread: ADS8900B, SN6501, TIDA-01035, , ADS127L21, ADS125H02, PGA855, UCC25800

Tool/software:

The traditional design used to rely on push-pull drivers.

Analog Devices and TI have used this solution in their EVMs. For example, TIDA-01035 uses the SN6501 to isolate the ADS8900B and AFE. Link to TIDA-01035

I have used the SN6501 in many designs. It works right out of the box, and I have never considered alternative solutions.

However, when I saw the release of the UCC25800-Q1, I began to question whether push-pull is still the best approach.

For example, considerations such as hard vs. soft switching or ZVS/ZCS switching, low inter-winding capacitance, and transformer leakage inductance being treated as a feature rather than a bug.

Now, for the question:

  • Can I use the UCC25800-Q1 as the isolated power supply for powering an isolated circuit consisting of the PGA855, ADS127L21, ADS125H02, several multiplexers, operational amplifiers, and an STM32U535, with less than 2W peak power consumption?

Requirements:

  1. Low-noise power rails after the LDOs.
  2. The highest possible insulation impedance, without significantly degrading the first requirement.
  3. Voltage rails: +15V, -15V, and +5V.

Design notes:

  • I am considering a resonant tank on the primary side.
  • I have an isolated CAN bus link between the isolated and PE sides.- SO I have kind of feedback link
  • On the PE side, I have an STM32H7, so I can control the frequency of the LLC using the UCC25800 Rt pin via the STM32 DAC.
  • Low and no-load control should not be an issue for the LLC.

I am asking this question because I am unsure if it is worth pursuing an unfamiliar path.

Best regards,
Mirtcho

  • 0
    TI__Mastermind 31665 points
    • "Can I use the UCC25800-Q1 as the isolated power supply for powering an isolated circuit consisting of the PGA855, ADS127L21, ADS125H02, several multiplexers, operational amplifiers, and an STM32U535, with less than 2W peak power consumption?"
      • Yes...total combined power of all the ICs you listed is not a limitation as long as you can operate within the VIN/Power limits given in the data sheet and you are comfortable with an unregulated output (similar that SN6501 is also unregulated)
      • Some of the LLC issues noted in your design notes seem like you are referring to a closed loop LLC. A closed loop LLC needs frequency modulation to maintain output regulation. A closed loop LLC requires very high frequency during start up and can have regulation issues at no/light load and wide input voltage. None of these apply to an open loop LLC power stage with fixed frequency.

    Regards,

    Steve