RP2350A + ADS1220 Molecule
Public Made by Adomby adom
24-bit thrust-acquisition molecule for the drone motor carrier: an RP2350A paired with a TI ADS1220 24-bit ADC, W25Q16JV flash and AP2112K-3.3 LDO, with a ratiometric load-cell front-end. Nests on the motor carrier over machine pins.
RP2350A + ADS1220 Molecule — Function
24-bit thrust acquisition. RP2350A (QFN-60) + ADS1220 + W25Q16JV + AP2112K-3.3, two differential load-cell channels. 26.40 × 36.00 mm, 4-layer, 70 placeable parts.
Signal chain
bridge -> [RF 2.49k 1%] -+- [CDIF 470n] -+- ADS1220 AINx
+- [CCM 47n 5%] -- GND (shared via per pair)
R sits at the contact end, C at the ADC end. A shared GND via per pair removes CM-to-DM conversion
error from CCM mismatch; CDIF >= 10 x CCM swamps the remainder.
Filter constants
VIN(MAX) = +/-[(AVDD - AVSS) - 0.4] / Gain = +/-36 mV at gain 128
PGA output stays 200 mV off each rail
CM window = 1.25 - 4.16 V Eq 12/13/14, Eq 14 dominates
f_cm / f_diff = 2(CDIF/CCM) + 1 = 21 f_diff 64.8 Hz, f_cm 1360 Hz
Noise 0.41 µVpp at gain 128 / 20 SPS. −3 dB bandwidth 13.1 Hz at 20 SPS, 39.6 Hz at 90 SPS (Table 8-4). Reference input current ±10 nA, buffered.
Ratiometric topology
REFP0 (pin 7), AVDD (pin 10), MC16 and MC23 all sit on the same +5V node, downstream of F1.
- Fuse drop and the AP2112's ~70 mA are common to reference and excitation, so they cancel
- Resistance from that node out to the cell is outside the loop and appears as gain error — ~0.029 % for 0.1 Ω, calibratable
Power
+5V_IN → F1 polyfuse → +5V → D1 SMF6.0A → GND. The fuse is upstream of the TVS, so a reverse
polarity fault drives TVS current through the fuse.
AP2112K-3.3 with 10 µF in (C5) and out (C6). C1 100 n sits 1.67 mm from AVDD.
Indicator
WS2812B-2020-V6 (C52917434). VIH is 0.55 × VDD and it runs from 3.3 V. Specifies 100 nF.
Not stocked at Mouser or DigiKey in the PLCC4 2020 package — LCSC only.
Board state
0 DRC violations, 0 unconnected. All 30 contacts on the 2 mm lattice, MP datum 16.000 × 32.000 mm.
Three silk DRC checks are ignored. Five BOM/schematic LCSC mismatches exist in
jlcpcb/project.db — the BOM generates from that database, not the schematic fields.
# RP2350A + ADS1220 Molecule — Function
24-bit thrust acquisition. RP2350A (QFN-60) + ADS1220 + W25Q16JV + AP2112K-3.3, two differential
load-cell channels. 26.40 × 36.00 mm, 4-layer, 70 placeable parts.
## Signal chain
```
bridge -> [RF 2.49k 1%] -+- [CDIF 470n] -+- ADS1220 AINx
+- [CCM 47n 5%] -- GND (shared via per pair)
```
R sits at the contact end, C at the ADC end. A shared GND via per pair removes CM-to-DM conversion
error from CCM mismatch; `CDIF >= 10 x CCM` swamps the remainder.
## Filter constants
```
VIN(MAX) = +/-[(AVDD - AVSS) - 0.4] / Gain = +/-36 mV at gain 128
PGA output stays 200 mV off each rail
CM window = 1.25 - 4.16 V Eq 12/13/14, Eq 14 dominates
f_cm / f_diff = 2(CDIF/CCM) + 1 = 21 f_diff 64.8 Hz, f_cm 1360 Hz
```
Noise 0.41 µVpp at gain 128 / 20 SPS. −3 dB bandwidth 13.1 Hz at 20 SPS, 39.6 Hz at 90 SPS
(Table 8-4). Reference input current ±10 nA, buffered.
## Ratiometric topology
REFP0 (pin 7), AVDD (pin 10), MC16 and MC23 all sit on the same `+5V` node, downstream of F1.
- Fuse drop and the AP2112's ~70 mA are common to reference and excitation, so they cancel
- Resistance from that node out to the cell is outside the loop and appears as gain error —
~0.029 % for 0.1 Ω, calibratable
## Power
`+5V_IN` → **F1 polyfuse → +5V → D1 SMF6.0A → GND**. The fuse is upstream of the TVS, so a reverse
polarity fault drives TVS current through the fuse.
AP2112K-3.3 with 10 µF in (C5) and out (C6). C1 100 n sits 1.67 mm from AVDD.
## Indicator
**WS2812B-2020-V6** (`C52917434`). VIH is 0.55 × VDD and it runs from 3.3 V. Specifies 100 nF.
Not stocked at Mouser or DigiKey in the PLCC4 2020 package — LCSC only.
## Board state
0 DRC violations, 0 unconnected. All 30 contacts on the 2 mm lattice, MP datum 16.000 × 32.000 mm.
Three silk DRC checks are ignored. Five BOM/schematic LCSC mismatches exist in
`jlcpcb/project.db` — the BOM generates from that database, not the schematic fields.