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UCD3138064A: DAC output for Envelop Tracking solution

Ella KIM
Expert 3862 points
Part Number: UCD3138064A
Other Parts Discussed in Thread: UCD3138, , UCD3138A

Hi Power Folks,

I'm looking at UCD3138 variants to see if it can implement Power Amplifier Envelop Tracking for 5G base station. I read two articles below : 

- Vout margining by DAC output 

https://www.ti.com/lit/an/snva802/snva802.pdf?ts=1641392717675&ref_url=https%253A%252F%252Fwww.ti.com%252Fsitesearch%252Fdocs%252Funiversalsearch.tsp%253FlangPref%253Den-US%2526searchTerm%253Denvelope%2Btracking%2526nr%253D578

- Vout margining by PWM 

https://www.ti.com/tool/PMP21697?keyMatch=&tisearch=search-everything&usecase=refdesign

DCDC can be implemented with UCD3138 or with discrete Buck. Whichever the DCDC stage would be, I wonder UCD3138 can be used for Vout margining. I believe PWM output for voltage margining can be done by DPWM port, and per I know UCD3138 does not provide DAC output. Could you let me know what 'DAC output' indicates in datasheet? I cannot find any detail.

As the ET for 5T requires very fast Vout transient settling time (customer is targeting <1us for now), I'm thinking UCD3138064A, which supports SPI (upto 25MHz) while UCD3138A supports I2C only (upto 400kHz).

Could you also advise if TI has ET solution or similar application with UCD3138? Could you share your thought on if the concept is feasible?

  • +1
    TI__Genius 17090 points

    The UCD has an internal 6 bit EADC (Error ADC) to provide the input to the compensation filter.  It has an internal DAC as one of the two inputs to the EADC, with the EADC output being the difference between the DAC value and the value from the power supply, which is typically output voltage or output current.  So Vout margining can be done in firmware easily, or you can track an external signal with an ADC and use it to set the DAC.  

    We have studied envelope tracking but have not come out with a solution.  It's not trivial to develop envelop tracking on the UCD.  It's digital filter can support a calculation rate of around 2 MHz, which may or may not be fast enough, depending on your requirements.  The EADC has a limited dynamic range to make its 64 ns conversion speed affordable.  It's 6 bits can be programmed for resolutions of 1, 2, 4, and 8 mV.  At the 8 mV setting, the range is +-256 mV.  The range of the DAC is 1.6 volts.  So the ability to do envelope tracking depends on your spec.  I don't know if its unfeasible, but it's probably far from trivial.