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feat(schematic): replace L7805 with TPS61088 boost converter (#1)

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# Bill of Materials — firstpcb (Stepper Driver + 12V Boost)
> **Branch:** `feat/boost-converter-integration`
> **Generated:** 2026-05-23
> **Estimated cost:** ~$50–80 first build (with combo kits) • ~$10/board in actually-used parts
---
## Critical Notes Before Ordering
| # | Issue | Impact |
|---|-------|--------|
| 1 | **BOM package field said "QFN-20 3.5×3.5mm"** for U1 | The actual TPS61088 RHL package is **VQFN-20, 4.5×3.5mm**. Your KiCad footprint is correct — only the BOM description was wrong (now fixed). |
| 2 | **PCB silkscreen reads `TPS61088QRHLRQ1`** (automotive Q1 variant), BOM lists `TPS61088RHLR` (commercial) | The commercial **TPS61088RHLR** is a fully drop-in substitute: same RHL package, same pinout. Use it — it's ~5× cheaper and far more available. |
| 3 | **U1 vs U2 designator mismatch** | Standalone `tps61088_boost.kicad_sch` test schematic uses U1; integrated `firstpcb.kicad_pcb` uses U2. Same part either way. |
| 4 | **TPS61088 pinout verified** | Schematic pins 1/3/4/5/6/7/8/9/11/12/15 = VIN/EN/SS-TR/COMP/FB/AGND/PGOOD/VOUT/BST/SW/PGND — matches TI datasheet exactly. ✅ |
| 5 | **L1 inductor substitution warning** | If swapping the Bourns SRP1265 for the cheaper TDK SPM10065, the footprint changes (12.6×12.6mm → 10.5×10mm). **Verify the KiCad footprint matches before ordering.** |
---
## Recommended Combo Kits (Buy These First)
These cover multiple BOM lines and stock you up for future builds:
| Kit | Covers | Est. Price | Source |
|-----|--------|-----------:|--------|
| **0805 E96 1% Resistor Sample Book** (170 values × 25pcs) | R1, R2, R3, R4, R5 + lifetime supply | ~$15–25 | [Amazon B09Z2RDW2F](https://www.amazon.com/Resistor-ohm-10M-Assorted-Resistance-Resistor-0805/dp/B09Z2RDW2F) |
| **0805 SMD Ceramic Cap Kit** (50V, 22pF–22µF) | C6, C8, C9 | ~$5–15 | [AliExpress multi-value kit](https://www.aliexpress.com/item/4000023618004.html) |
| **1206 22µF 25V X5R 50-pack** (CL31A226KAHNNNE) | C4, C5, C10, C11 | ~$8 | [AliExpress 50-pack](https://www.aliexpress.com/item/32751090379.html) |
| **JST-XH 2.54mm Connector Kit** (560pcs, 2–6 pin housings + crimps + headers) | StepperConnection1 | ~$8–12 | Search `JST-XH 2.54mm kit 560pcs` |
| **JST-EH 2.5mm 3-pin Kit** (housing + crimps + header) | SW1 | ~$4–6 | Search `JST-EH 2.5mm 3-pin housing crimp` |
> **Why the kit approach:** R3 (30.1K) and R4 (190K) are E96 values that aren't in basic E24 kits. Buying a proper E96 sample book is cheaper than ordering five individual reels and means you'll have every standard value for future projects.
---
## Single-Part Key Items
Parts that can't be combo'd — order these individually:
| Ref | Part | Source | Price | Notes |
|-----|------|--------|------:|-------|
| **U1** | TPS61088RHLR | [LCSC C87357](https://www.lcsc.com/product-detail/DC-DC-Converters_TI_TPS61088RHLR_TPS61088RHLR_C87357.html) | ~$0.61 | 14k in stock. Drop-in for the Q1 variant on the silkscreen. |
| **L1** | TDK SPM10065VT-2R2M-D (2.2µH, 16.6A) | [LCSC C1015860](https://www.lcsc.com/product-detail/Inductors-SMD_TDK-SPM10065VT-2R2M-D_C1015860.html) | ~$1.50 | Cheaper alternative to Bourns SRP1265. **Verify footprint match.** |
| **L1 (alt)** | Bourns SRP1265A-2R2M (2.2µH, 22A) | DigiKey | ~$2–3 | Matches original BOM footprint exactly. |
| **C3** | 100µF 25V SMD electrolytic, 6.3×5.8mm | AliExpress 10-pack | ~$2–3 | JAMICON/Lelon equivalents are fine. Verify pad layout. |
| **A4988** | Stepper driver module + heatsink, 5-pack | AliExpress | ~$5–8 | Any reputable seller. Heatsinks included. |
| **MotorPower1** | KF301-5.0-3P screw terminal, 10-pack | [AliExpress](https://www.aliexpress.com/item/32842003333.html) | ~$0.70 | Generic part. |
---
## Full BOM (with Purchase column)
### Active components
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| ESP32-WROOM1 | ESP32-C3-DevKitM-1 | Module | 1 | **SKIP** — user sources separately | Pinout-specific module from a special supplier. Do not order. |
| A4988 | A4988 Driver | Pololu breakout | 1 | AliExpress 5-pack (~$5–8) | Heatsink included. |
| U1 | TPS61088RHLR | VQFN-20 4.5×3.5mm (RHL) | 1 | [LCSC C87357](https://www.lcsc.com/product-detail/DC-DC-Converters_TI_TPS61088RHLR_TPS61088RHLR_C87357.html) (~$0.61) | Non-Q1 substitute for `TPS61088QRHLRQ1` on PCB. |
### Resistors — all covered by 0805 E96 sample book
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| R1 | 10K | 0805 1% | 1 | E96 kit | Pull-up / standard. |
| R2 | 10K | 0805 1% | 1 | E96 kit | |
| R5 | 10K | 0805 1% | 1 | E96 kit | |
| R3 | 30.1K | 0805 1% | 1 | E96 kit | Feedback divider — must be 1%. |
| R4 | 190K | 0805 1% | 1 | E96 kit | Feedback divider — must be 1%. |
### Capacitors — small values covered by 0805 ceramic kit
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| C8 | 47pF | 0805 C0G/NP0 50V | 1 | 0805 ceramic kit | C0G preferred, X7R OK at this value. |
| C9 | 100nF | 0805 X7R 50V | 1 | 0805 ceramic kit | Decoupling. |
| C6 | 22nF | 0805 X7R 50V | 1 | 0805 ceramic kit | TPS61088 compensation cap. |
### Capacitors — bulk (all covered by one 50-pack)
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| C4 | 22µF | 1206 X5R 25V | 1 | [AliExpress 50-pack](https://www.aliexpress.com/item/32751090379.html) (~$8) | CL31A226KAHNNNE ≡ GRM31CR61E226KE15L. **25V+ required** (12V output rail). |
| C5 | 22µF | 1206 X5R 25V | 1 | Same 50-pack | |
| C10 | 22µF | 1206 X5R 25V | 1 | Same 50-pack | |
| C11 | 22µF | 1206 X5R 25V | 1 | Same 50-pack | |
### Single-part caps & inductor
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| C3 | 100µF | SMD aluminum electrolytic, 6.3×5.8mm, 25V | 1 | AliExpress 10-pack (~$2–3) | Verify pad layout matches KiCad `CP_Elec_6.3x5.8` footprint. |
| L1 | 2.2µH | Shielded SMD power inductor | 1 | [LCSC TDK SPM10065VT-2R2M-D](https://www.lcsc.com/product-detail/Inductors-SMD_TDK-SPM10065VT-2R2M-D_C1015860.html) (~$1.50) **or** Bourns SRP1265A-2R2M (~$3) | **CRITICAL: must handle ≥10A.** Avoid no-name AliExpress inductors — saturation current often misrated. Footprint differs between TDK and Bourns. |
### Connectors & terminals
| Ref | Value | Pkg | Qty | Purchase | Notes |
|-----|-------|-----|----:|----------|-------|
| SW1 | B3B-EH-A | JST EH 3-pin THT, 2.5mm pitch | 1 | JST-EH 2.5mm 3-pin kit (~$4–6) | Get the kit — you need matching housings + crimps too. **EH series, not XH.** |
| MotorPower1 | KF301-5.0-3P | 3-pin screw terminal, 5mm pitch THT | 1 | [AliExpress 10-pack](https://www.aliexpress.com/item/32842003333.html) (~$0.70) | Generic; any KF301-5.0-3P works. |
| StepperConnection1 | B4B-XH-A | JST XH 4-pin THT, 2.54mm pitch | 1 | JST-XH 2.54mm kit (~$8–12) | Get the multi-pin kit; covers this build + future projects. |
---
## Sources
- [TPS61088 product page (TI)](https://www.ti.com/product/TPS61088/part-details/TPS61088RHLR)
- [LCSC TPS61088RHLR (C87357)](https://www.lcsc.com/product-detail/DC-DC-Converters_TI_TPS61088RHLR_TPS61088RHLR_C87357.html)
- [LCSC TDK SPM10065VT-2R2M-D (C1015860)](https://www.lcsc.com/product-detail/Inductors-SMD_TDK-SPM10065VT-2R2M-D_C1015860.html)
- [AliExpress 22µF 25V 1206 50-pack](https://www.aliexpress.com/item/32751090379.html)
- [AliExpress KF301-5.0-3P 10-pack](https://www.aliexpress.com/item/32842003333.html)
- [Amazon 170-value 0805 E96 1% resistor sample book](https://www.amazon.com/Resistor-ohm-10M-Assorted-Resistance-Resistor-0805/dp/B09Z2RDW2F)
- [Bourns SRP1265A-2R2M datasheet](https://bourns.com/products/magnetic-products/details/power-inductors-smd-high-current-shielded/srp1265a)