Adds four general-purpose I/O pins to a host over I2C/SMBus. Each of the four pins (P0-P3) is independently set as input or output through a configuration register, and the host reads or drives them over a two-wire bus at a fixed address, so a microcontroller short on pins gains four more without extra wiring. Power-on default is all inputs. A small, cheap way to break out a handful of switches, LEDs, or enable lines.

Pinout

Pin	Name	Type	Function
1	P0	bidirectional	P-port bit 0. Push-pull bidirectional I/O; configurable as input or output via the Configuration register. Powers up as an input with a weak pull-up to VCC. High-current drive (up to ~25 mA sink) sufficient for direct LED drive.
2	P1	bidirectional	P-port bit 1. Push-pull bidirectional I/O; configurable as input or output via the Configuration register. Powers up as an input with a weak pull-up to VCC.
3	P2	bidirectional	P-port bit 2. Push-pull bidirectional I/O; configurable as input or output via the Configuration register. Powers up as an input with a weak pull-up to VCC.
4	GND	power_in	Device ground return. Connect to the system ground plane.
5	P3	bidirectional	P-port bit 3. Push-pull bidirectional I/O; configurable as input or output via the Configuration register. Powers up as an input with a weak pull-up to VCC.
6	SCL	input	I2C serial clock input. Open-drain bus line; connect to VCC through an external pull-up resistor. Supports standard mode (100 kHz) and fast mode (400 kHz).
7	SDA	bidirectional	I2C serial data line. Open-drain bidirectional bus; connect to VCC through an external pull-up resistor.
8	VCC	power_in	Supply voltage input, 2.3 V to 5.5 V. Bypass locally with a ceramic decoupling capacitor to GND.

Key specifications

Parameter	Value
Type	4-bit I2C / SMBus I/O expander
Interface	I2C / SMBus (fixed address)
I/O	4 pins (P0-P3), each input or output
Supply	2.3-5.5 V
Bus speed	Up to 400 kHz
Default	All I/O as inputs at power-on
Package	SOIC-8

Ordering variants

Same part, different packaging or reel option.

PCA9536D (SOIC-8, tube)
PCA9536DR (SOIC-8, tape & reel)
PCA9536DGKR (VSSOP-8)

CAD (KiCad official)

Symbol: Interface_Expansion:PCA9536D (KiCad official)
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D, STEP)

Provenance

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

Datasheet: Texas Instruments datasheet (35 pp, sha256 bc9e7a06865817ab, 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