astra/f1c100s

docs/bulk-capacitors.md

# Bulk capacitor selection

All seven rail reservoirs use 0805 land patterns on the bottom of the module. The three 10 µF TV/reference filter capacitors also use 0805 bottom-side footprints. Dedicated 100 nF processor decouplers remain on top with their direct pin branches. This is now a two-sided assembly.

| Role | Part | Nominal | Rating | Dielectric | Typical capacitance under DC bias |
|---|---|---|---|---|---|
| Six rail reservoirs and three TV/reference filters | GRM21BR61E106KA73L | 10 µF | 25 V | X5R | 7.21 µF at 3.3 V; 9.50 µF at 1.8 V |
| DRAM rail reservoir | GRM219R71E105KA88D | 1 µF | 25 V | X7R | 0.978 µF at 1.8 V |
| Six carrier regulator input/output reservoirs | GRM21BR71C475KE51L | 4.7 µF | 16 V | X7R | 3.31 µF at 5 V; 4.13 µF at 3.3 V |

The carrier regulator reservoirs remain on top and also use 0805 footprints. Capacitance values are unchanged from the original circuit. Larger packages do not guarantee the full nominal capacitance in service.

Typical values were interpolated from Murata's product-characteristics API on 2026-09-13 at 25 °C, with 1 Vrms test amplitude for the 10 µF and 1 µF parts and 0.5 Vrms for the 4.7 µF part. These are typical model results, not guaranteed minima; tolerance, temperature, aging and operating AC amplitude also matter. No PDN simulation or hardware measurements have been performed.

Sources: [10 µF part](https://pim.murata.com/en-us/pim/details/?partNum=GRM21BR61E106KA73%23), [1 µF part](https://pim.murata.com/en-us/pim/details/?partNum=GRM219R71E105KA88%23), [4.7 µF part](https://pim.murata.com/en-us/pim/details/?partNum=GRM21BR71C475KE51%23). Each product page exposes the C–DC-bias curves used here.