0hmX/dual-usb-peltier-assembly

docs/general-pd-driver.md

# General USB-C PD Peltier driver

## Scope and limits

One two-wire output with adjustable constant-voltage and constant-current limits. **PD POWER** supplies the load; **USB PROGRAM** provides native USB configuration, firmware updates and logic power. There are no display, buttons or display headers. Three status LEDs and 16 bare copper debug pads support setup and development.

The default module is [HiLetgo TEC1-12706, Amazon ASIN B00M1PM7H6](https://www.amazon.com/dp/B00M1PM7H6). Its listing specifies 40 × 40 × 3.6 mm and two modules per package; this board drives one. During selection, that listing showed 50+ purchases in the past month, 564 ratings and 4.3/5; [diymore's TEC1-12706 listing](https://www.amazon.com/dp/B01IUVSSHW) showed 100+, 354 ratings and 4.4/5. These changing, potentially pooled listing statistics support choosing a familiar consumer module, without establishing the world's best-selling Peltier.

The [Hebei reference datasheet](https://www.hebeiltd.com.cn/peltier.datasheet/TEC1-12706.pdf) describes a related TEC1-12706 variant with 6.4 A maximum, 14.4 V maximum and 50 W maximum heat pumping at a 25 °C hot side. It does not certify the Amazon batch. Qualify purchased samples and their thermal installation; electrical watts are not watts of cooling.

| Setting | Prototype target |
| --- | --- |
| Factory defaults | 12.0 V / 5.50 A, OFF until saved or explicitly started |
| Saved profile | Starts after approximately 1 s of qualified PD input |
| Voltage ceiling | 2.1–15.0 V, 0.1 V steps |
| Current ceiling | 0.50–6.00 A, 0.05 A steps |
| Power ceiling | 72 W nominal selected V × I |
| Power input | Qualified 20 V / 5 A contract; 100 W source and 5 A e-marked cable |
| Programming input | USB 2.0 data and 5 V logic supply |
| Fan output | Fixed 12 V, 0.5 A / 6 W continuous budget; qualified PD only |
| Temperature ports | Two independent powered DS18B20 inputs on GPIO8 / GPIO9 |
| Board | 100 × 80 mm, 1.6 mm, four layers, no traces or vias |

Voltage is regulated **before the 10 mΩ shunt**, which drops approximately 55 mV at 5.5 A plus wiring losses. USB STATUS reports approximate voltage at the TEC terminal. The 2.1 V setting floor provides nominal margin above the converter's 2 V current-sense common-mode accuracy boundary after the shunt. Current regulation under overload can reduce output below that boundary; low-voltage accuracy and short-circuit behavior need bench validation. IC, shunt and divider tolerances remain uncalibrated.

For other modules, set ceilings within their allowed operating limits, allowing for tolerances. A two-wire Peltier provides no identity or ratings to the driver. This revision monitors both temperatures and powers a fan; it does not regulate temperature or reverse polarity.

## Power and control architecture

`100 W PD source → 5 A cable → qualified PFET path → TPS55289 CC/CV stage → 10 mΩ shunt → Peltier`

- **CYPD3177** requests MIN=MAX=20 V and COARSE=5 A/FINE=0. Two common-source AO4407A PFETs gate raw power into the qualified rail. Specify firmware 3.10D or later/date code after 2047 because [Infineon documents older minimum-voltage behavior](https://community.infineon.com/t5/Knowledge-Base-Articles/CYPD3177-EZ-PD-BCR-Device-Firmware-Updates/ta-p/251759). PD-port D+/D− are unconnected. VDDD has 1 µF and two 100 nF bypasses.
- **TPS55289** integrates its four power MOSFETs and an average-output-current loop using ISP/ISN and the shunt. MODE is grounded for I²C address 0x75. A 130 kΩ / 10 kΩ EN divider gives approximately 17.22 V UVLO; PD FAULT independently clamps EN.
- **Logic power:** LMR50410 supplies auxiliary 5 V from raw PD VBUS. TPS2116 selects the higher of that rail and programming USB 5 V, with reverse blocking between ports. Its output, `LOGIC_5V`, supplies converter VCC and the TLV75533 3.3 V regulator. Programming USB has no path to qualified PD VIN or the TEC. At qualified PD input, the auxiliary supply provides the converter's required external VCC operating voltage. Converter EN remains LOW during programming-only power.
- **USB PROGRAM:** RP2040 provides native USB CDC and ROM BOOTSEL/UF2 flashing. Both CC pins have separate 5.1 kΩ sink resistors; orientation pairs connect to USB_DP/USB_DM through USBLC6-2SC6 protection and separate 27 Ω series resistors at the MCU. The protection's VBUS bias uses local LOGIC_5V to avoid its steering diodes backfeeding the programming connector. Firmware detects that connector's VBUS separately and disconnects USB when absent. The Abracon ABM8-272-T3 12 MHz crystal uses two 15 pF loads and a 1 kΩ damping resistor. W25Q128JVSIQ supplies 16 MiB QSPI flash. These choices follow [Raspberry Pi’s hardware guide](https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdf).
- **Attach capacitance:** raw PD has 7.1 µF nominal (4.7 µF USB, 2.2 µF auxiliary input and two 100 nF bypasses), or 8.52 µF with a blanket +20%. Raw PROGRAM has 1 µF. Both are below the [10 µF receptacle limit described by TI](https://www.ti.com/document-viewer/lit/html/SSZTB15/GUID-9C081873-D60C-462A-ABFB-9A4E87F564F0); downstream switched-bank inrush still needs measurement.
- **Reset safety:** an NPN clamps converter EN by default, biased from LOGIC_5V. An NMOS releases it only while MCU GPIO2 actively grants permission; its gate has a pull-down. GPIO2 is separate from the ROM USB/QSPI boot interface. MCU reset, blank firmware, lost control supply and watchdog reset remove permission.
- **Startup:** valid saved settings start after one second of qualified input. Before OE=1, firmware verifies PD, releases EN into reset-OFF state, writes and reads back voltage/current/protection registers, and checks PD again. A CRC/version-checked profile occupies the reserved final 4 KiB flash sector at XIP address 0x10FFF000, excluded by the linker; saving requires OFF and readback verification. No profile or invalid flash leaves output OFF. Unplugging USB PROGRAM does not stop an operating load.
- **Faults:** SC/OVP, ADC, measured-limit and converter-communication failures latch OFF. STOP cancels automatic start for the current PD session. Source detach stops output; after at least one second without PD, a new qualified connection can use the saved profile unless a protective fault remains latched. Explicit RUN retries all startup checks; CLEAR resets the latch while remaining OFF. [Firmware instructions](../firmware/README.md) explain watchdog/reset behavior.

Internal feedback ratio 0.0752 caps converter DAC full-scale at about 15.96 V. Software selects at most 15 V and enforces V × I ≤72 W. Allow a further 6 W for the fan plus both converters' losses and logic power under the 100 W input budget. This budget is not an independent input-current limit; the PD controller requests current but does not itself measure/enforce it.

The first-pass switching network uses approximately 395 kHz, a 4.7 µH coil, four 10 µF / 50 V input MLCCs plus 100 µF / 35 V bulk, four 22 µF / 25 V pre-shunt MLCCs, and 100 µF / 25 V post-shunt bulk. Sense filtering is 10 Ω per tap plus 220 nF differential. Compensation starts with TI EVM values of 27.4 kΩ / 4.7 nF / 100 pF. Validate these over the full range and actual capacitor DC bias. At assumed 90% efficiency, 72 W output requires 80 W before auxiliary/connector losses; continuous capability is unmeasured. Lower-power PD contracts are rejected.

## Temperature probes and fan power

The default probes are two units from the [HiLetgo DS18B20 five-pack, Amazon B00M1PM55K](https://www.amazon.com/dp/B00M1PM55K), with 1 m factory cables. The live Amazon selection showed **In Stock**, **Amazon's Choice**, **100+ bought in the past month**, **378 ratings**, and **4.5/5**. The [selection snapshot](sensor-sourcing.json) records the observation and geometry limits. These are popularity signals for the selected listing.

Both XY302V-3.5-3P terminals use **pin1=3V3/red, pin2=DATA/yellow, pin3=GND/black**. Separate 4.7 kΩ pull-ups and 100 Ω series resistors connect HOT to RP2040 GPIO8 (physical pin11) and COLD to GPIO9 (physical pin12), with local bypassing and USBLC6-2SC6 data-line protection. The selected terminal accepts 16–26 AWG wire. Use one externally powered probe per port; parasite power is unsupported. Check the wire assignments when substituting another seller's probe.

The [DS18B20 datasheet](https://www.analog.com/media/en/technical-documentation/data-sheets/ds18b20.pdf) specifies the 1-Wire protocol, ROM and scratchpad CRC, and up to 750 ms conversion time. Firmware schedules conversions in the background and reports `hot_c`, `cold_c`, validity, age and status through USB. Missing or invalid probes report null values and do not block saved-profile startup. This is temperature monitoring, with no thermal cutoff or setpoint control. Other 3.3 V digital probes can use the GPIO ports with appropriate firmware; compatible I²C devices can use the existing SDA/SCL/3V3/GND debug pads. The I²C converter uses address 0x75.

A dedicated [TI LMR50410XDBVR](https://www.ti.com/lit/ds/symlink/lmr50410.pdf) buck converts qualified PD to fixed 12 V. Its 1 V feedback reference and 110 kΩ / 10 kΩ divider set nominal 12.0 V. A 33 µH coil and two 22 µF / 25 V output capacitors follow the manufacturer's 12 V reference topology. VIN and EN both use `VBUS_QUALIFIED`, so programming-only power cannot run the fan. The fan stays powered when the TEC output is stopped. The regulator is rated 1 A; the user-facing continuous fan budget is 0.5 A and is not a precision hardware current clamp.

The keyed **Molex 47053-1000** header connects **pin1=GND, pin2=12V, pin3=tach NC, pin4=PWM NC**. [Noctua's primary PC fan specification](https://noctua.at/pub/media/wysiwyg/Noctua_PWM_specifications_white_paper.pdf) identifies this header and describes compatible fans' full-speed behavior without a PWM signal. Use a 12 V fan within the continuous and startup supply ratings; 24 V fans and high-current server fans are outside this output's intended range.

The selected fan is the **[Noctua NF-A8 PWM, Amazon B00NEMG62M](https://www.amazon.com/dp/B00NEMG62M)**, the standard beige/brown 12 V model. [Noctua's specifications](https://www.noctua.at/en/products/nf-a8-pwm/specifications) give **0.08 A maximum / 0.96 W**, a factory 4-pin plug and 200 mm sleeved cable, **2200 rpm**, **32.67 CFM**, an SSO2 bearing and **six-year warranty**. It plugs directly into the existing header and runs at full speed with PWM unconnected; use the direct cable without the Low-Noise Adaptor. The 80 × 80 × 25 mm frame is 81 × 81 × 27 mm with its anti-vibration pads. Amazon US showed **In Stock**, **$17.95**, **500+ bought in the past month**, **4.9/5 with 2,269 ratings**, sold by **Noctua Cooling Solutions** and shipped by **Amazon**, checked 14 October 2026. [The selection record](fan-sourcing.json) distinguishes US availability from other delivery regions. The fan and cable are external accessories; the PCB circuit and purchased JLC BOM are unchanged. The assembly shows connectivity and does not specify the hot-side heatsink or establish thermal performance.

## Parts, cables and debug

| Role | Selected source |
| --- | --- |
| Peltier | [HiLetgo TEC1-12706, Amazon B00M1PM7H6](https://www.amazon.com/dp/B00M1PM7H6) |
| Both temperature probes | [HiLetgo DS18B20 five-pack, Amazon B00M1PM55K](https://www.amazon.com/dp/B00M1PM55K); two used, 1 m factory leads |
| Fan and factory cable | [Noctua NF-A8 PWM 12 V, Amazon B00NEMG62M](https://www.amazon.com/dp/B00NEMG62M); one used, 200 mm factory cable, 0.08 A maximum |
| Both probe terminals | Xinlaiya XY302V-3.5-3P, C784941; three positions, 3.5 mm pitch, 16–26 AWG |
| Fixed 12 V fan supply | TI LMR50410XDBVR, C2841056 / Sunlord SWPA8040S330MT, C83467 |
| PC fan header | Molex 47053-1000, C240840; [manufacturer drawing](https://www.molex.com/content/dam/molex/molex-dot-com/products/automated/en-us/salesdrawingpdf/470/47053/470531000_sd.pdf) |
| PD sink | CYPD3177-24LQXQT, C2952489; [Infineon datasheet](https://www.infineon.com/assets/row/public/documents/24/49/infineon-cypd3177-24lqxq-datasheet-en.pdf) |
| Both USB receptacles | GCT USB4085-GF-A, C7095263; [manufacturer](https://gct.co/connector/usb4085), 5 A rating |
| PD PFET pair | AO4407A, C16072; [AOS datasheet](https://www.aosmd.com/sites/default/files/res/datasheets/AO4407A.pdf) |
| CC/CV converter | TPS55289RYQR, C5942077; [TI datasheet](https://www.ti.com/lit/ds/symlink/tps55289.pdf), [EVM](https://www.ti.com/tool/TPS55289EVM) |
| Main inductor | Bourns SRP1265A-4R7M, C780205; [manufacturer drawing](https://www.bourns.com/docs/product-datasheets/srp1265a.pdf) |
| Current shunt | TA-I RLM25FEER010, C192580; 10 mΩ, 1%, 2 W |
| Native USB MCU | Raspberry Pi RP2040, C2040; [datasheet](https://datasheets.raspberrypi.com/rp2040/rp2040-datasheet.pdf) |
| MCU flash / crystal | Winbond W25Q128JVSIQ, C97521 / Abracon ABM8-272-T3, C20625731; [official reference design](https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdf) |
| Reverse-blocking logic mux | TPS2116DRLR, C3235557; [TI datasheet](https://www.ti.com/lit/ds/symlink/tps2116.pdf) |
| USB data protection | USBLC6-2SC6, C7519; [ST datasheet](https://www.st.com/resource/en/datasheet/cd00050750.pdf) |
| Auxiliary 5 V / logic 3.3 V | LMR50410Y5FQDBVRQ1, C2871822 / TLV75533PDBVR, C404027; [buck](https://www.ti.com/lit/ds/symlink/lmr50410-q1.pdf), [LDO](https://www.ti.com/lit/ds/symlink/tlv755p.pdf) |
| Output terminal | KEFA KF301-5.0-2P, C474881; catalog 17 A, 14–22 AWG; sustained-current temperature needs qualification |
| POWER / RUN / FAULT | Yellow KT-0603Y C2287 / green KT-0603YG C2289 / red KT-0603R C2286 |
| Both USB cables | [Cable Matters 201440](https://www.cablematters.com/pc-1532-123-usb-c-20-charging-cable-with-240w-power-delivery.aspx), 1 m, 5 A, e-marked, USB 2.0 data |

[Inventory](component-sourcing.csv) records **134 purchased placements across 54 exact JLC SKUs**. The [timestamped stock snapshot](jlc-stock-audit.json) and CSV retain direct JLC product URLs, stock and observation times for the current board. Stock and pricing change; the tscircuit parts engine’s availability warnings are separate from these direct catalog observations and netlist validation. No fabrication or component order has been placed.

Use factory Peltier leads in the terminal; seller lengths/gauges vary. Cable extensions require their own current/temperature qualification. Both selected USB cables support data, although PD POWER uses only power/CC. The model distinguishes their roles by color and labels; these are illustrative cable shapes.

POWER indicates 3.3 V logic supply, RUN indicates enabled output and FAULT indicates a latched fault. The **16 debug pads** expose SWDIO, SWCLK, BOOTSEL, RUN/reset, 3V3, GND, raw PD, qualified PD, LOGIC5V, TEC terminal, pre-shunt output, driver EN, ISP, ISN, SCL and SDA. They are 1.5 mm copper pads, with no fitted component or JLC SKU. BOOTSEL connects to QSPI chip-select through 1 kΩ; hold it to GND during reset to enter the ROM loader without buttons. Silkscreen keeps these functional labels, port names, polarity and LED labels; automatic component reference text is hidden.

## Assembly and qualification

The default entrypoint contains a native `assembly.device`, with the board and `assembly.part` CAD geometry visible together in the local dev server's **3D** tab. This follows the [tscircuit assembly API](https://docs.tscircuit.com/guides/advanced-assembly). Peltier and cable geometry add no PCB footprints or electrical nets. The installed `assembly.cable` API requires PCB connector or motor endpoints; these external accessories use explicit geometry tied to the actual board connectors without introducing artificial peripheral PCBs.

The assembly export consumes the final circuit JSON and actual placement. Imported supplier meshes are identified as supplier CAD. Eleven native accessories show the Peltier, two USB cables, two TEC leads, both probe bodies and cables, and the Noctua fan with its factory cable. The fan uses manufacturer CAD; the Amazon Peltier uses its listed envelope, while probe housings and cable routes illustrate connectivity. [Provenance](../assets/assembly/provenance.json) records sources and fallbacks, and generated provenance includes the circuit JSON hash. These models are not fit-qualified mechanical CAD.

The preview omits the required hot-side heatsink, cold plate, clamping and thermal interface. Fit these before operation. The board is a power driver rather than a complete refrigeration assembly.

Before manufacture, route/review power and return copper, Kelvin sensing, decoupling, gate drive, USB data, EMI/ESD and heat spreading. Bench-check USB enumeration/UF2/recovery; both orientations and simultaneous supplies; backfeed/inrush; saved-profile startup and corrupt/interrupted saves; PD detach/reset; current/voltage tolerances and compensation; short circuit and output-off discharge; watchdog/control-supply loss; and sustained connector/cable/board temperatures. Native tests and a firmware cross-build do not establish these measurements.