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This is a follow up to my last question on Low power circuit design for turning an LDO on/off at specific voltage levels, where I wanted to find a low power way to turn an LDO on/off at specific voltage levels. The issue there was that the circuit has some unwanted behavior for input voltages between 1 and 2V. Thus I decided to make a new circuit, which I want to discuss in a new post.

I redesigned the circuit and got rid of the LDO as well as the voltage monitor and replaced them with a TPS63805 buck-boost converter. This converter also provides a power good (pg) signal, which I am now using to turn the output to the e-paper on/off. Since the converter can also boost the voltage I am now able to utilize more of the stored energy of my supercap between the voltages 1.8 to 5.5V instead of 2.6 to 5.5V.

Questions:

  • Q1: Is this a better approach than the one in the previous question?
  • Q2: Are there still better (even lower power) alternatives?
  • Q3: Would it make sense to have hysteresis for turning on/off power to the e-paper due to the initial high energy demand right after it gets powered on?

New circuit: enter image description here

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  • \$\begingroup\$ Personally, I feel more confident about this approach given that you have the MOSFET to turn on/off your load controlled from the PG signal. \$\endgroup\$
    – Andy aka
    Commented Nov 6, 2023 at 8:56
  • \$\begingroup\$ @Andyaka I guess I will proceed with testing the new circuit then. \$\endgroup\$
    – enwi
    Commented Nov 6, 2023 at 12:09
  • \$\begingroup\$ I'd wait until you get some more feedback. No feedback is not great but, it usually means folk think it's OK. \$\endgroup\$
    – Andy aka
    Commented Nov 6, 2023 at 12:49
  • \$\begingroup\$ Good point @Andyaka \$\endgroup\$
    – enwi
    Commented Nov 6, 2023 at 19:40
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    \$\begingroup\$ I was hoping for more feedback, but accepted your answer now :) \$\endgroup\$
    – enwi
    Commented Jan 27 at 22:09

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Q1: Is this a better approach than the one in the previous question?

I believe it is superior and probably the best way to achieve your aims. If I remember correctly from the previous question, you couldn't accept an output voltage that "came up" slowly and, that seemed to be the killer on the previous design. With the power good ("PG") signal on the buck-boost converter you can unambiguously activate the P channel MOSFET and apply power to your load very quickly (milliseconds if not microseconds).

Q2: Are there still better (even lower power) alternatives?

There may be but nothing is springing to mind. The buck-boost converter is about 90% efficiency for a decent range of input voltages and unless you can find one that is a bit better I'd stick with this one: -

enter image description here

When it transitions into buck mode, the efficiency is more like 95%. Pretty good of course. I guess the AO3401A could be improved upon: -

enter image description here

Having said that the maximum gate threshold voltage is nice and low.

Q3: Would it make sense to have hysteresis for turning on/off power to the e-paper due to the initial high energy demand right after it gets powered on?

I believe the TI buck-boost has hysteresis built in. Maybe read the data sheet.

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