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PAC1934 current-sense resistors R72–R75 have no values specified

Aperta
  • Qualcosa non va?
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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
25/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Tranquilla
Ambito
embedded-iot

Direzione di ricerca

Start by inspecting the schematic and BOM entries for U32 and R72–R75, tracing each SENSE1+/− through SENSE4+/− net to identify the monitored rail. Determine the expected maximum current and suitable resistor package and value for each channel, then update the schematic and BOM. Done means all four resistors have validated values and ratings before assembly.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

bug

Summary

R72, R73, R74, and R75 are the four current-sense resistors for U32 (PAC1934 4-channel power monitor). None of these resistors have a value assigned in the schematic or BOM — they are placed as generic R0805 footprints with no value attribute.

R72: bschulz_passives R-EU_ R0805  (no value)
R73: bschulz_passives R-EU_ R0805  (no value)
R74: bschulz_passives R-EU_ R0805  (no value)
R75: bschulz_passives R-EU_ R0805  (no value)

Without a defined sense resistance, it is impossible to:

  1. Calculate power/current from PAC1934 ADC counts
  2. Specify the correct part for assembly
  3. Ensure the sense voltage (V_sense = I × R_sense) falls within the PAC1934 input range (±100 mV full scale)
  4. Ensure sense resistor power dissipation is acceptable

PAC1934 sense resistor sizing

The PAC1934 measures differential voltage across the sense resistor. Per the PAC1934 datasheet:

  • Full-scale input range: ±100 mV (can be scaled via product register)
  • Minimum detectable current depends on R_sense value

For each channel, select R_sense based on the maximum expected current:

R_sense = V_full_scale / I_max = 0.1 V / I_max

Example for 100 mA max: R_sense = 1 Ω (100 mW at full scale — too high for 0805)
Example for 500 mA max: R_sense = 200 mΩ
Example for 1 A max: R_sense = 100 mΩ

For 0805 package at 125 mW rated power, maximum continuous current:

I_max = √(P / R_sense)
  • At 100 mΩ: I_max = √(0.125 / 0.1) = 1.12 A (OK for moderate current channels)
  • At 10 mΩ: I_max = 3.5 A (suitable for high-current channels like the main battery)

Questions to resolve

  1. Which rail does each channel (SENSE1–SENSE4) monitor? The schematic shows R72 on one channel, R73 on another, etc. — identify which net each is in series with.
  2. What is the expected maximum current on each monitored rail?
  3. Are 0805 resistors appropriately rated for the power dissipation? For high-current channels, larger packages (1206, 2512) or parallel resistors may be needed.

Affected components

  • U32: PAC1934T-I/JQ (16-UQFN, 4-channel power monitor)
  • R72, R73, R74, R75: sense resistors (0805, value TBD)
  • Nets: SENSE1+/−, SENSE2+/−, SENSE3+/−, SENSE4+/−

Action required

Assign resistance values to R72–R75 based on the expected current in each monitored channel. Update BOM and schematic before assembly.

🤖 Generated with Claude Code

Lingua principale
G-code
Stelle
8
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2
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Come iniziare

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  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

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