Texas Instruments TCA8424RHAR

Overview

TCA8424RHAR from Texas Instruments is a low-voltage 8×16 keyboard scanner IC with HID-over-I²C interface, operating from 1.65V to 3.6V, supporting FM+ I²C up to 1 MHz, scanning up to 128 keys, and generating 8-byte INPUT reports for up to six simultaneous key presses - deployed in Windows 8–compatible laptop/notebook keyboards.

For engineers reviewing the TCA8424RHAR datasheet, TCA8424RHAR pinout, TCA8424RHAR application, or TCA8424RHAR equivalent, this page delivers verified technical context, real-world HID report behavior, LED sink capability (12 mA), interrupt timing, and preprogrammed keyboard map compatibility - all grounded in TI's SCDS341 production data sheet.

Technical Context

The TCA8424RHAR implements a dedicated key-scan engine with internal oscillator, row/column multiplexing logic, and hard-coded HID/Report descriptors compliant with Microsoft's HID over I²C v1.0 specification. It uses volatile input/output registers backed by non-volatile memory storing keyboard map (256 B), usage IDs, and report IDs.

Its I²C interface supports standard and fast-mode plus (1 MHz), with fixed slave address 0x76 (write) / 0x77 (read), ACK/NACK protocol, and built-in noise filtering on SCL/SDA. The device asserts active-low INT on key press/release and clears it only upon reading the full input report - not via GET_REPORT command.

Key Specifications

Pinout & Package

Package: 32-pin RHB (5 mm × 5 mm, 0.5 mm pitch, thermal pad). Pin count and layout match TI's RHB package drawing SCDS341.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar keyboard scanner applications.

Compared with TCA8424RGER, the TCA8424RHAR provides full 16-row support and larger package thermal margin; compared with TCA8424RHAT, it offers identical functionality at lower cost for applications within 85°C ambient - making RHAR the balanced choice for mainstream Windows-compatible keyboards.

Availability

TCA8424RHAR is available at Aetrix Electronics and suitable for laptop keyboard interfaces, industrial HMI keypads, medical control panels, and POS terminal designs requiring stable component supply, long-lifecycle support, and Windows 8+ HID compliance.

Supply support for TCA8424RHAR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity solutions, with decades of expertise in human-interface and power-efficient mixed-signal ICs.

The TCA8424 product line was designed specifically for HID-over-I²C keyboard applications in Windows 8+ platforms - integrating scan logic, descriptor storage, and I²C protocol handling into a single low-voltage, small-footprint IC.

FAQ

What is the I²C slave address of the TCA8424RHAR?

The TCA8424RHAR uses a fixed 7-bit I²C slave address of 0x76 for write operations and 0x77 for read operations, as defined in Table 1 of TI's SCDS341 datasheet. This address is hard-coded and not user-configurable; alternate addresses require special-order variants coordinated through TI sales.

Does the TCA8424RHAR support more than two LEDs?

No - the TCA8424RHAR variant supports exactly two open-drain LED outputs (LED0 and LED1), each capable of sinking up to 12 mA. Other variants like TCA8424RHA support up to eight LEDs, but RHAR's pinout and internal configuration are limited to two.

How does the TCA8424RHAR handle simultaneous key presses?

The TCA8424RHAR generates an 8-byte INPUT report that supports up to six simultaneous non-modifier key presses plus eight modifier keys (e.g., Ctrl, Shift, Alt). The first byte is the modifier byte; bytes 5–10 contain usage IDs - satisfying USB HID keyboard report requirements for N-key rollover.

Is the keyboard map preprogrammed in the TCA8424RHAR?

Yes - the TCA8424RHAR ships with a factory-programmed keyboard map compatible with standard laptop/notebook layouts. However, it is also available unprogrammed (TCA8424RHAR-UNPROG) for custom key mapping, and the NV memory can be reprogrammed in-system using TEST pin and HID commands.

What happens to the INT pin after a key release on the TCA8424RHAR?

The TCA8424RHAR asserts INT on both key press and key release. The INT signal remains asserted until the host reads the full 8-byte input report - specifically, it clears after the eighth byte is read. Using GET_REPORT does not clear INT; only a complete register read resets the interrupt flag.

Can the TCA8424RHAR operate at 1.65 V while maintaining full 1 MHz I²C speed?

Yes - TI's SCDS341 datasheet specifies FM+ I²C operation up to 1 MHz across the entire 1.65 V to 3.6 V supply range. Electrical characteristics including rise/fall times, setup/hold times, and ACK timing are validated down to 1.65 V, ensuring robust high-speed communication in ultra-low-voltage systems.