0hmX/simplified-am62l-computer

docs/USB_C_POWER_QUALIFICATION.md

# USB-C 5 V source-current qualification

This board remains a USB Type-C sink/UFP with no USB data and no USB Power
Delivery. The TUSB320LAI detects the source's Rp advertisement before the
TPS259470 eFuse is allowed to connect `PROTECTED_5V`.

## Implemented logic

- `CC1` and `CC2` connect directly from the receptacle to TUSB320LAI pins 1
  and 2. The former discrete 5.1 kΩ resistors were removed; the controller's
  UFP/dead-battery Rd terminations provide that function.
- `PORT` is tied low for UFP, `ADDR` is left open for GPIO mode, and `EN_N` is
  tied low. `VBUS_DET` is fed from `VBUS_RAW` through 909 kΩ, 1%, which is
  within TI's 855 kΩ to 920 kΩ range.
- TUSB320LAI VDD is connected directly to `VBUS_RAW`, before the eFuse, and
  has a local 100 nF bypass capacitor.
- A TLV75533PDBVR generates `AON_3V3` from `VBUS_RAW` for the OUT1/OUT2
  pull-ups and logic. It has the required 1 µF input and output capacitors.
- OUT1 has a 4.7 kΩ pull-up to `AON_3V3` and drives an SN74LVC1G04 inverter.
  The inverter output drives TPS259470 `EN/UVLO`; a 100 kΩ pull-down on
  `EFUSE_EN` holds the eFuse off while the always-on logic is unpowered.
- In GPIO UFP mode, OUT1 is high for unattached/default-current states and low
  for 1.5 A or 3 A advertisements. Thus the inverter enables the eFuse only
  for the two sufficient-current states.
- OUT2 is also pulled up with 4.7 kΩ. A second inverter plus an
  SN74LVC1G08 decodes OUT1=high and OUT2=low to illuminate the red
  `WEAK USB SUPPLY` LED only for an attached default-current source.
- Raw-VBUS nominal capacitance is 5.8 µF (4.7 µF bulk + 1 µF LDO input +
  0.1 µF TUSB320 bypass), inside TI's 1 µF to 10 µF UFP guidance.

## TPS259470 current limit

TI gives:

`R_ILM (ohms) = 3334 / I_ILM (amps)`

With 2.49 kΩ, 1%:

- nominal: `3334 / 2490 = 1.339 A`
- resistor-only range: `1.326 A` to `1.353 A`
- including the datasheet's ±10% current-limit accuracy for limits above 1 A,
  the conservative upper calculation is
  `3334 / (2490 × 0.99) × 1.10 = 1.488 A`

That is below a 1.5 A Type-C advertisement, but the worst-case calculated
margin is only about 12 mA. Production validation must measure current limit
across temperature and component lots; no unlisted tolerance is assumed.

## Startup safety

At power-off, the 100 kΩ `EFUSE_EN` pull-down keeps TPS259470 disabled. When
raw VBUS arrives, OUT1 is pulled high as `AON_3V3` rises, so the inverter
continues to drive `EFUSE_EN` low. The TUSB320LAI starts as an unattached sink
and only pulls OUT1 low after it detects an attached source advertising 1.5 A
or 3 A. This sequence has no logic state that intentionally enables the eFuse
for an unattached or default-current source.

## Exact JLCPCB/LCSC parts

| Function | Part | LCSC |
| --- | --- | --- |
| CC controller | TUSB320LAIRWBR | C132554 |
| eFuse enable inverter | SN74LVC1G04DBVR | C7827 |
| weak-source inverter | SN74LVC1G04DBVR | C7827 |
| weak-source AND gate | SN74LVC1G08DBVR | C7666 |
| always-on 3.3 V LDO | TLV75533PDBVR | C404027 |
| 2.49 kΩ, 1% ILM resistor | 0402WGF2491TCE | C25884 |
| 909 kΩ, 1% VBUS_DET resistor | 0402WGF9093TCE | C25799 |
| red LED | LTST-C190KRKT | C94869 |

## Official sources

- [TI TUSB320LAI datasheet, Rev. D](https://www.ti.com/lit/ds/symlink/tusb320lai.pdf)
- [TI TPS25947 datasheet, Rev. C](https://www.ti.com/lit/ds/symlink/tps25947.pdf)
- [TI TLV755P datasheet, Rev. D](https://www.ti.com/lit/ds/symlink/tlv755p.pdf)