Analog Devices Inc./Maxim Integrated MAX6955AAX+

Overview

MAX6955AAX+ from Maxim Integrated is a 2-wire (I²C-compatible) LED display driver with integrated I/O expander and key-scan controller, operating from 2.7V to 5.5V. It drives up to 16 digits of 7-segment, 8 digits of 14-segment, or 8 digits of 16-segment displays - or 128 discrete LEDs - while providing five GPIOs configurable as a 32-key matrix scanner with automatic debouncing and n-key rollover. It is used in panel meters and set-top box front panels requiring compact, low-EMI display control with simultaneous user input handling.

For engineers reviewing the MAX6955AAX+ datasheet, MAX6955AAX+ pinout, MAX6955AAX+ application, or MAX6955AAX+ equivalent, this page delivers verified technical context, real-world drive capability, confirmed I²C timing (400kbps), validated GPIO key-scan behavior, and precise package mapping to the 36-pin SSOP - all critical for embedded display subsystem design and BOM validation.

Technical Context

The MAX6955AAX+ integrates a programmable RC oscillator (1–8MHz) or external clock input for multiplex timing, with dedicated OSC_OUT for synchronized blink across multiple drivers. Its dual-plane digit RAM (P0/P1) enables hardware-managed blinking without host intervention, and its character generator includes 104 ASCII glyphs for 14/16-segment displays plus hexadecimal font for 7-segment use.

Segment drivers are slew-rate limited (11mA/µs) to suppress EMI, and intensity is controlled digitally via 16-step per-digit PWM brightness. The five GPIOs (P0–P4/IRQ) support configurable pull-up current (75µA at 3.3V), hysteresis (0.03×V+), and IRQ assertion on key debounce - all operating across the full −40°C to +125°C automotive temperature range.

Key Specifications

Pinout & Package

MAX6955AAX+ is housed in a 36-pin SSOP (Shrink Small Outline Package) with exposed paddle internally connected to GND for thermal management. Pin 1 is located at the top-left corner adjacent to the index mark.

Key Features

Applications

Availability

MAX6955AAX+ is available at Aetrix Electronics and suitable for panel meters, set-top box front panels, and white goods control interfaces requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6955AAX+ 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

Maxim Integrated (now part of Analog Devices) designs precision analog and mixed-signal ICs for industrial, automotive, and consumer applications, emphasizing integration, reliability, and thermal robustness.

The MAX6955AAX+ belongs to Maxim's display interface and I/O expansion product line, engineered specifically for embedded HMI systems needing compact, low-power LED driving with concurrent user input handling - eliminating separate key-scan ASICs or FPGA logic.

FAQ

What is the maximum number of keys the MAX6955AAX+ can scan, and how is debouncing handled?

The MAX6955AAX+ supports scanning up to 32 keys in matrix configuration with fully hardware-based debouncing and n-key rollover. Debounce timing is fixed at 10ms per key transition and occurs autonomously - no host firmware involvement is needed. When a key press is detected and debounced, the P4/IRQ pin asserts low, signaling the host microcontroller to read the key state register. This eliminates software debounce routines and ensures deterministic response in real-time HMI applications using the MAX6955AAX+.

Does the MAX6955AAX+ support both common-anode and common-cathode LED displays?

The MAX6955AAX+ supports only common-cathode LED displays. Its O0–O7 outputs function as digit drivers that sink current from display common cathodes, while O0–O18 serve as segment drivers that source current to display anodes. It does not provide high-side (anode-switching) digit drivers. For common-anode displays, external high-side drivers or redesign would be required - the MAX6955AAX+ datasheet explicitly specifies operation with common-cathode configurations only.

How is segment current set on the MAX6955AAX+, and what is the typical range?

Segment current on the MAX6955AAX+ is set externally via a single resistor (RSET) connected between the ISET pin and GND. With V+ = 3.3V and VLED = 2.2V, typical segment source current is −32mA (min) to −48mA (max), adjustable by selecting RSET value per the datasheet equation. The current is matched across all 19 segment outputs to within ±5%, ensuring uniform LED brightness. This single-resistor method avoids per-segment trimming and simplifies production calibration for the MAX6955AAX+.

Can the MAX6955AAX+ drive mixed display types (e.g., 7-segment and 14-segment) simultaneously?

Yes, the MAX6955AAX+ supports mixed display types through its digit-type register, which configures four independent digit drive slots. Each slot can be assigned to 7-segment, 14-segment, or 16-segment formats - for example, two slots driving 7-segment digits and two slots driving 14-segment characters. The internal font generator automatically selects the correct glyph map (hexadecimal for 7-seg, ASCII for 14/16-seg) based on slot configuration, enabling heterogeneous displays on a single MAX6955AAX+ without external logic.

What is the function of the OSC_OUT pin on the MAX6955AAX+, and how is it used in multi-driver systems?

The OSC_OUT pin on the MAX6955AAX+ provides a buffered copy of the internal or external multiplex clock, enabling precise blink synchronization across multiple MAX6955AAX+ devices. In multi-driver systems, OSC_OUT from one device drives the OSC input of others, ensuring identical blink phase and period - critical for seamless visual continuity across large displays. Unlike raw OSC, OSC_OUT is push-pull (not open-drain), eliminating need for external pullups and supporting reliable fanout to ≥4 downstream MAX6955AAX+ units.