calculate components for voltage regulation

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calculate components for voltage regulation #2

Closed securelyfitz closed 1 year ago

securelyfitz commented 1 year ago

RP2040 reference schematic has a 1117 LDO regulator with 10uF capacitors on input and output To use a 1.5v battery (or anything else), a TI TPS613221A is only a few cents more and will boost low voltages while tolerating higher voltages. Need to calculate inductor and capcitor sizes.

securelyfitz commented 1 year ago

calculations are hard. TI's TPS613221A dev board uses the following. will copy and test:

150 uF tantalum capacitor on input T520B157M006ATE070 - only on dev board, for long power supply lines. Not necessary for usb 5v
4.7 uH inductor - DFE252012F-4R7M=P2, 74438335047, or SDEM25201B-4R7MS
22 uF ceramic output capacitor GRM21BZ71A226ME15

securelyfitz commented 1 year ago

Turns out the sot23-3 TPS613221A isn't available except by special order. I found the natlinear XT1861 that is the same footprint but IDK about quality. Will test the natlinear, plus another cheap alternative, but have a couple sot23-5 TPS* on order to test if the others don't work.

securelyfitz commented 1 year ago

XT1861 is working great, just need to fix the footprint on the board

securelyfitz commented 1 year ago

rolled up into #12