PCA9557

@@ -0,0 +1,61 @@+# PCA9557++**Texas Instruments** · I2C I/O expander · HVQFN-16++Adds eight general-purpose I/O pins over I2C, each set as input or output through a configuration register, with a hardware RESET input that returns the device to its power-on state on demand. A polarity-inversion register lets active-low inputs read as active-high without host logic, and three address pins put up to eight devices on one bus. It runs from 2.3 to 5.5 V. A compact, resettable I/O expander for switches, LEDs, and enable lines.++## Pinout++| Pin | Name | Type | Function |+|---|---|---|---|+| 1 | A0 | input | Hardware I2C address input bit 0. Tie directly to VCC or GND to program the device's I2C slave address (up to 8 devices per bus). |+| 2 | A1 | input | Hardware I2C address input bit 1. Tie directly to VCC or GND. |+| 3 | A2 | input | Hardware I2C address input bit 2. Tie directly to VCC or GND. |+| 4 | IO0 | bidirectional | P-port I/O bit 0. High-impedance open-drain output structure; requires an external pullup to VCC when driven high. Configured as input at power-on. |+| 5 | IO1 | bidirectional | P-port I/O bit 1. Push-pull output; sinks up to 25 mA to drive LEDs directly. Input at power-on. |+| 6 | VSS | power_in | Ground reference for supply and I/O. |+| 7 | IO2 | bidirectional | P-port I/O bit 2. Push-pull output; 25 mA sink capability. Input at power-on. |+| 8 | IO3 | bidirectional | P-port I/O bit 3. Push-pull output; 25 mA sink capability. Input at power-on. |+| 9 | IO4 | bidirectional | P-port I/O bit 4. Push-pull output; 25 mA sink capability. Input at power-on. |+| 10 | IO5 | bidirectional | P-port I/O bit 5. Push-pull output; 25 mA sink capability. Input at power-on. |+| 11 | IO6 | bidirectional | P-port I/O bit 6. Push-pull output; 25 mA sink capability. Input at power-on. |+| 12 | IO7 | bidirectional | P-port I/O bit 7. Push-pull output; 25 mA sink capability. Input at power-on. |+| 13 | RESET | input | Active-low reset input. Asserting low reinitializes the registers and I2C/SMBus state machine. Tie to VCC through a pullup if unused. |+| 14 | VDD | power_in | Supply voltage, 2.3 V to 5.5 V. Decouple with a 0.1 µF ceramic capacitor to GND close to the pin. |+| 15 | SCL | input | I2C serial clock input. Requires an external pullup resistor to VCC. Supports 100 kHz standard mode and 400 kHz fast mode. |+| 16 | SDA | bidirectional | I2C serial data line, open-drain bidirectional. Requires an external pullup resistor to VCC. |++## Key specifications++| Parameter | Value |+|---|---|+| Type | 8-bit I2C I/O expander |+| Interface | I2C (up to 400 kHz) |+| I/O | 8 pins (IO0-IO7) |+| Reset | Hardware RESET input |+| Polarity | Per-pin inversion register |+| Addresses | 8 (A0-A2) |+| Supply | 2.3-5.5 V |+| Package | HVQFN-16 |++## Ordering variants++- `PCA9557PW (TSSOP-16)`+- `PCA9557BS (HVQFN-16)`+- `PCA9557D (SOIC-16)`++## CAD (KiCad official)++- Symbol: `Interface_Expansion:PCA9557BS (KiCad official)`+- Footprint: `Package_DFN_QFN:HVQFN-16-1EP_3x3mm_P0.5mm_EP1.5x1.5mm`+- 3D model: HVQFN-16 (KiCad packages3D, STEP)++## Provenance++Data extracted from the manufacturer datasheet, not a distributor listing:++- **Datasheet:** [Texas Instruments datasheet](https://www.ti.com/lit/ds/symlink/pca9557.pdf) (47 pp, sha256 `d55cbe207fbcb26d`, retrieved 2026-08-17, tier: manufacturer)+- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.+- **CAD:** KiCad official libraries (CC-BY-SA 4.0).++[Datasheet PDF](docs/pca9557-datasheet.pdf)

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