Diodes Incorporated AH3978Q-WT-7

Overview

AH3978Q-WT-7 from Diodes Incorporated is an AEC-Q100 Grade 0 qualified dual Hall-effect latch IC delivering two independent open-drain speed outputs (Q1 and Q2) for precise rotational direction and speed sensing in automotive systems. It operates from 2.7V to 27V, features chopper-stabilized architecture for ±0.35% magnetic offset drift over temperature, integrated self-diagnostics for ISO 26262 ASIL-B readiness, and operates across –40°C to +150°C ambient.

For engineers reviewing the AH3978Q-WT-7 datasheet, AH3978Q-WT-7 pinout, AH3978Q-WT-7 application, or AH3978Q-WT-7 equivalent, key selection criteria include dual-output timing alignment (tDC = 50–1000 ns), magnetic matching tolerance (±30 G between Q1/Q2 BOP/BRP), thermal shutdown at +165°C with auto-restart, and TSOT25 package compatibility with anti-pinch motor control PCB layouts.

Technical Context

The AH3978Q implements two independent Hall plates (H1 and H2) with separate signal chains-each including chopper stabilization, offset cancellation, sample-and-hold, and output control logic-to generate synchronized but electrically isolated Q1 and Q2 speed signals. Its functional safety architecture continuously monitors internal voltage regulator, Hall bias, and diagnostic logic blocks.

Output behavior is defined by magnetic field polarity and slew rate: Q1 activates on south-pole approach to the branded side (B > +50 G), Q2 activates on north-pole approach (B < –50 G), with hysteresis of 120–180 G ensuring noise immunity. The device enters safe mode upon detection of UVLO (VDD < 2.0 V), overtemperature (>+165°C), or internal diagnostic fault.

Key Specifications

Pinout & Package

TSOT25 (Type A1) surface-mount package: 2.9 mm × 2.8 mm × 0.8 mm body, 0.95 mm pitch, matte tin-plated leads, moisture sensitivity level 1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-output Hall latch applications.

Compared with MLX92232 and A1262, the AH3978Q-WT-7 delivers native dual-output synchronization, full AEC-Q100 Grade 0 qualification, and integrated functional safety mechanisms - reducing BOM count and validation effort in ASIL-B automotive designs.

Availability

AH3978Q-WT-7 is available at Aetrix Electronics and suitable for automotive power closures, transmission gear detection, electric power steering motor control, and steering angle backup systems requiring stable component supply across extended temperature and voltage ranges.

Supply support for AH3978Q-WT-7 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

Diodes Incorporated is a global semiconductor manufacturer specializing in discrete, analog, and mixed-signal solutions for automotive, industrial, and consumer markets.

The AH3978Q belongs to Diodes' AEC-Q100-qualified Hall-effect sensor family, engineered specifically for functional safety-critical automotive motion sensing - emphasizing magnetic accuracy, thermal resilience, and integrated diagnostics.

FAQ

What distinguishes AH3978Q from AH3975Q/AH3976Q/AH3977Q?

The AH3978Q provides two independent open-drain speed outputs (Q1 and Q2), whereas AH3975Q–AH3977Q deliver speed (SP) and direction (DIR) outputs. AH3978Q's dual-speed architecture enables phase-based direction decoding without relying on output polarity inversion, offering tighter timing alignment (tDC = 50–1000 ns) and improved magnetic matching (±30 G) for high-precision rotary applications.

How does the self-diagnostic function operate in AH3978Q?

The AH3978Q continuously monitors its internal voltage regulator, Hall bias current, chopper clock, and output driver stages. Upon detecting a fault - such as regulator dropout, Hall plate open-circuit, or clock stall - it forces both Q1 and Q2 into high-impedance state and holds them there until the fault clears or power cycles. Diagnostic status is not communicated externally; safe-mode entry is implicit via output freeze.

Can AH3978Q-WT-7 be used with 5 V logic systems?

Yes. Although AH3978Q-WT-7 operates from 2.7 V to 27 V, its open-drain outputs are compatible with 5 V pull-up resistors. The output saturation voltage remains ≤0.5 V at 10 mA load, ensuring valid logic-low levels for standard TTL and CMOS interfaces. No level-shifting circuitry is required when interfacing with 5 V MCUs or FPGAs.

What is the recommended PCB layout practice for minimizing magnetic interference?

Place the AH3978Q-WT-7 with its branded marking side facing the target magnet, maintaining ≥1.45 mm clearance between Hall plates (H1/H2) and PCB copper traces. Avoid routing high-current or high-frequency traces beneath the package; use the suggested TSOT25 pad layout (C = 0.95 mm, X = 0.55 mm, Y = 0.70 mm) to ensure mechanical stability and thermal dissipation. Ground planes should be solid under pins 2 and 3 only.