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EXTVcc current consumption of three different devices

Hello. I’m designing a power supply unit for high (up to 60°C) ambient temperature application. Vin range is from 8 to 80V. All frequencies will be synchronized to 200kHz clock. It consists of:

  1. LTC3779: 24Vout, 10A output current at 12Vin (in reality it would never peak above 8-9A), unnecessary loads will be turned off, when Vin drops down to 8V, DRVCC = 10V;
  2. LTC7801, 6Vout, 5A output current, DRVCC = 10V;
  3. LT8490, 12.6V 1A LiPo charger, MPPT off,  possible modifications for higher voltage batteries

In order to decrease heat on LDOs, I’ve been thinking of switching from LTC3779 to LTC3777, which could potentially provide voltage for EXTVcc for all three cotrollers from its bias supply. I’m not sure, how much current all three devices would consume on average and what safety margin should I add. The LTSpice simulation shows that LTC3779 never draws more than 25mA from 12V source at EXTVCC pin, but in the LTC3777 datasheet I see 38mA current, LTC3779 — 48mA, LTC7801 - 32mA, and LT8490 datasheet doesn't provide any information. I suppose that even LTC3639 might not be enough for this with its 100mA output current. Should I move to LTC3638?

  • Can you be more specific about what you want to achieve? There is no LDO on the parts that you mentioned. These parts should be able to operate at 60degC ambient temperature. Perhaps a block diagram will help.

    For item 1, if input will only be 12Vin down to 8Vin, you may only need a boost converter and not necessarily use LTC3779.

    The input range is quite wide. You have to make sure the converter is able to deliver the output power for the input range.

  • I want to integrate a micropower buck converter which would provide 12V to EXTVCC pin of all three controllers (which is path to internal onboard LDOs). I’m not sure how much current all three regulators would draw through that pin, which means that LTC3639 for example might not provide enough current. I want to do that in order to make the whole device more efficient and decrease possibility of failures.

    The item 1 has range of 8 to 80 Vin, I just mentioned the worst case of input.

  • I would recommend that you connect to a local ADI FAE or sales team who can provide more support. I'm not so sure if having a separate LTC3639 to power internally would be cost efficient.