Adds eight general-purpose I/O pins over I2C, each set as input or output through a configuration register, with an active-low RESET input that returns the device to its power-on state on demand. An open-drain INT output flags a change on any input so the host is told which pin moved without polling, and two address pins allow several devices on one bus. It runs from 1.65 to 5.5 V. A compact, resettable I/O expander for panels of buttons, LEDs, and enables.

Pinout

Pin	Name	Type	Function
1	RESET	input	Active-low reset input. Connect to VCC through a pull-up resistor if no active connection is used. Asserting resets the device to its default (power-on) state.
2	IO0	bidirectional	P-port I/O bit 0. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
3	IO1	bidirectional	P-port I/O bit 1. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
4	IO2	bidirectional	P-port I/O bit 2. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
5	IO3	bidirectional	P-port I/O bit 3. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
6	VSS	power_in	Ground reference for supply and all I/O signals.
7	IO4	bidirectional	P-port I/O bit 4. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
8	IO5	bidirectional	P-port I/O bit 5. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
9	IO6	bidirectional	P-port I/O bit 6. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
10	IO7	bidirectional	P-port I/O bit 7. Push-pull design structure. IOH = -10 mA, IOL = 25 mA (recommended). Powers up as input.
11	INT	output	Open-drain active-low interrupt output. Asserts when an input P-port changes state. Connect to VCC through a pull-up resistor. IOL(typ) = 7 mA at VOL = 0.4 V.
12	SCL	input	I2C serial clock input. Connect to VCC through a pull-up resistor. Supports 100-kHz Standard-mode and 400-kHz Fast-mode.
13	SDA	bidirectional	I2C serial data bus (open-drain). Connect to VCC through a pull-up resistor. IOL(typ) = 3 mA at VOL = 0.4 V.
14	VDD	power_in	Supply voltage input, 2.3 V to 5.5 V. Bypass to GND with a local decoupling capacitor.
15	A0	input	I2C hardware address input bit 0. Connect directly to VCC or GND to select one of four slave addresses. VIH >= 0.7 x VCC; VIL <= 0.3 x VCC.
16	A1	input	I2C hardware address input bit 1. Connect directly to VCC or GND to select one of four slave addresses. VIH >= 0.7 x VCC; VIL <= 0.3 x VCC.

Key specifications

Parameter	Value
Type	8-bit I2C I/O expander
Interface	I2C (up to 400 kHz)
I/O	8 pins (IO0-IO7)
Interrupt	INT output (interrupt-on-change)
Reset	Hardware RESET input
Addresses	4 (A0-A1)
Supply	1.65-5.5 V
Package	VQFN-16

Ordering variants

Same part, different packaging or reel option.

PCA9538PW (TSSOP-16)
PCA9538RGVR (VQFN-16)
PCA9538ADBR (SSOP-16, variant address)

CAD (KiCad official)

Symbol: Interface_Expansion:PCA9538BS (KiCad official)
Footprint: Package_DFN_QFN:NXP_VQFN-16-1EP_4x4mm_P0.65mm_EP2.1x2.1mm
3D model: VQFN-16 (KiCad packages3D, STEP)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Texas Instruments datasheet (44 pp, sha256 7bbc8724cd47ce44, 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