Analog Devices Inc./Maxim Integrated MAX6921AUI+T

Overview

MAX6921AUI+T from Maxim Integrated is a 20-output, 76V vacuum-fluorescent display (VFD) tube driver with 4-wire serial interface (CLOCK, DATA, LOAD, BLANK), push-pull CMOS high-voltage outputs sourcing up to 40mA continuously, and operating across -40°C to +125°C - used in static or multiplexed VFD modules for industrial weighing and gaming machine front panels.

For engineers reviewing the MAX6921AUI+T datasheet, MAX6921AUI+T pinout, MAX6921AUI+T application, or MAX6921AUI+T equivalent, this page delivers verified electrical specs, cascading capability via DOUT, BLANK-driven PWM intensity control, TSSOP-28 package mapping, and real-world VFD system integration context - all confirmed against Maxim's official 19-3020 Rev 1 datasheet.

Technical Context

The MAX6921AUI+T implements a 20-bit serial-to-parallel shift register with transparent output latches, clocked by a 5MHz industry-standard 4-wire interface. Its outputs swing rail-to-rail from VBB (8V–76V) to GND, supporting both anode and grid driving in static or multiplexed VFDs.

Each output features slew-rate-controlled CMOS push-pull structure (typical 40Ω source / 750Ω sink), with rise/fall times of 0.9µs/0.6µs (VBB = 60V, CL = 50pF). The active-high BLANK input forces all 20 outputs low independently of latch state and enables direct PWM intensity modulation without serial reconfiguration.

Key Specifications

Pinout & Package

MAX6921AUI+T is housed in a lead-free, RoHS-compliant 28-pin TSSOP package (package code U28+1), with 0.65mm pitch, exposed pad optional, and thermal resistance θ_JA = 78.1°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar VFD driver applications.

Compared with MAX6931AUI+ and MAX6922ATL+, the MAX6921AUI+T uniquely combines daisy-chain capability (DOUT), hardware PWM (BLANK), and 20-channel density in TSSOP-28 - making it optimal for cost-sensitive, medium-complexity VFD systems requiring flexible display expansion.

Availability

MAX6921AUI+T is available at Aetrix Electronics and suitable for industrial weighing scales, gaming machine front panels, and avionics instrumentation requiring stable component supply across extended temperature and high-reliability environments.

Supply support for MAX6921AUI+T 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, mixed-signal, and high-voltage ICs for industrial, automotive, and communications markets - with emphasis on robustness, integration, and system-level power efficiency.

The MAX6921AUI+T belongs to Maxim's VFD driver product line, engineered specifically for reliable, high-brightness vacuum-fluorescent display control in harsh environments - prioritizing wide supply range, rail-to-rail output drive, and simplified serial interface architecture.

FAQ

What is the maximum VBB voltage the MAX6921AUI+T can safely handle?

The MAX6921AUI+T has an absolute maximum VBB rating of +80V, with recommended operating range of 8V to 76V. Operation at 76V is fully characterized across temperature and load; exceeding 76V risks violating the VBB–GND breakdown limit and may cause permanent damage even if within the 80V absolute max. Always use appropriate overvoltage protection on the VBB rail when deploying MAX6921AUI+T in systems with potential transients.

Can the MAX6921AUI+T drive both VFD grids and anodes simultaneously?

Yes, the MAX6921AUI+T can drive either grids or anodes on any of its 20 outputs - each OUTx pin is a bidirectional push-pull switch capable of sourcing up to 40mA (to VBB) or sinking up to 4mA (to GND). In multiplexed configurations, outputs are typically assigned as grids (sourcing) and anodes (sinking), while static displays may use all outputs as anodes. No external components are needed to reconfigure the role of each output.

Does the MAX6921AUI+T require a negative supply voltage (VSS)?

No, the MAX6921AUI+T does not require or support a VSS pin - it is designed for unipolar operation with outputs swinging from VBB to GND only. The VSS pin exists exclusively on the MAX6931 variant. Using MAX6921AUI+T eliminates the need for a negative bias supply, simplifying power design and reducing BOM cost in applications where filament biasing is handled externally or not required.

How does the DOUT pin enable cascading of multiple MAX6921AUI+T devices?

The DOUT pin of the MAX6921AUI+T outputs the same 20-bit data stream that was shifted in via DIN, delayed by exactly 20 CLK cycles plus propagation delay (tDO ≤150ns). By connecting DOUT of one MAX6921AUI+T to DIN of the next, and sharing CLK/LOAD/BLANK, a chain of N devices receives sequential 20-bit words - enabling control of 20×N outputs with only four MCU pins. Cascading is fully functional at 5MHz when VCC ≥4.5V.

What is the purpose of the BLANK input, and how is it used for PWM intensity control?

The BLANK input is an active-high signal that forces all 20 outputs low regardless of latch state, turning off the VFD instantly and placing the MAX6921AUI+T in low-power shutdown. For PWM intensity control, a fixed-frequency (e.g., 100–500Hz) square wave is applied to BLANK - the duty cycle directly determines average display brightness without altering serial data or requiring MCU rewrites. This hardware-based method ensures flicker-free dimming and frees MCU resources.