CD3217 and T2 Power on Sequence
If a CD3217 does not have the LDO outputs, test the lines for shorts, otherwise the chip is missing power or bad.
Data sheet of closest Ti chip.
A bad CD3217 can often cause a loop at step 10. All of the CD3217s need to be fully functional and communicate with the SMC before the CD3217 connected to the charger will request 20V
These documents are for specific boards, but will likely apply to most T2 Mac. Any net names and designators will be specific to the board it is from.
820-01055
820-01598
T2 Power rails resistances (820-01700)
PPVDDCPU_AWAKE 10-15 Ohm
PP0V82_SLPDDR 30-40 Ohm
PPVDDCPUSRAM_AWAKE 100-120 Ohm
PP1V1_SLPS2R 1-2 kOhm
PP0V9_SLPDDR 40 Ohm
PP1V8_SLPS2R 4 kOhm
820-001700 CD3217 Compatibility issues
CD3217s from 2020/M1 boards will not work.
Symptoms of compatibility issue: PPBUS ~12.30, all ports are switching to 19V with T2 boot/or one side will turn 19v, another stays on 5v (19v 0.05-0.1A) there will be a visible heat spot on T2 1st pin corner (inner side since T2 itself is approx 2 smaller than IC)
Device will start from charged battery, there will be no issue with usb devices but charger wont be recognized.
To solve you need full set of compatible CD3217, just pair wont help as well as tbt rom swap, DFU Recovery, etc.
Generally 001700 behaviour is very inconsistent. some boards might start with only one cd3217 present on board (should be the one connected to tbt rom of course), some will stuck in 5V 0.2A, some will stuck in 19v 0.1A(basically same power consumption).
Probably there are multiple revisions of the board, images pending. If you can add some more info, please report your revision / cd3217 behaviour below.
820-001700 CD3217 revisions list
Case 1: MacBook Pro 16" 2019 With CD3217 rev. 9AP0NVQ No power with one side of newer 12P1FXQ(took from 2020 board), Symptoms: quick T2 boot, 19V mode + hot T2 Corner on original side, 5v 0.2A on another. PPBUS 12.3V
820-01987
CD3217 B12 09P09CQ
Possibly alternative revision with TI logo on chip, CD3217 B12 02P04ES
820-01598
CD3217 B12 97P146Q