Allegro MicroSystems A3935KLQ

Overview

A3935KLQ from Allegro MicroSystems is a 3-phase N-channel MOSFET gate driver IC designed for automotive high-power motor control. It integrates a PFM boost converter (16 V nominal), internal LDO-regulated 13.5 V gate supply (VREG), six TTL-compatible gate drive outputs, and a differential current-sense amplifier with 19.2 V/V gain. It operates across –40°C to 150°C junction temperature and supports battery input from 7 V to 40 V.

For engineers reviewing the A3935KLQ datasheet, A3935KLQ pinout, A3935KLQ application, or A3935KLQ equivalent, key selection considerations include its integrated bootstrap circuitry for high-side N-FETs, diagnostic fault reporting (short-to-battery/ground, bridge-open, over/undervoltage), dead-time control (75–180 ns), and AEC-Q100 qualified operation in engine bay and EPS systems.

Technical Context

The A3935KLQ implements a pulse-frequency modulated (PFM) boost converter to generate a stable ~16 V VBOOST rail from low-voltage automotive batteries (7–40 V), feeding an internal LDO that delivers regulated 13.5 V (±0.65 V) to high-side gate drivers. Its six independent gate outputs-three high-side (GHA/GHB/GHC) and three low-side (GLA/GLB/GLC)-are directly controlled via TTL-level inputs (AHI/ALO, etc.) with propagation delay ≤150 ns and shoot-through prevention via programmable dead time (75–180 ns).

It embeds a precision current-sense amplifier (CSP/CSN inputs) with ±35 µA input offset, 1.6 MHz small-signal bandwidth, and rail-to-rail output (0.075 V to VDD–0.25 V), enabling accurate phase-current monitoring in 3-phase BLDC or stepper motor drives. Fault detection includes VBAT overvoltage (adjustable 19.4–40 V), undervoltage (5.0–5.5 V), VREG undervoltage (9.9–11.1 V), thermal shutdown (160–180°C), and Kelvin-connected drain-source monitoring via VDRAIN/VDSTH.

Key Specifications

Pinout & Package

Package: 36-pin QSOP (LQ), 0.8 mm pitch, surface-mount, lead-free variant with 100% matte tin plating. Dimensions: 15.30 mm × 10.31 mm × 2.64 mm max height.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-phase gate driver applications.

Compared with MP6532GQ-Z and TLE9183QX, the A3935KLQ uniquely combines PFM boost conversion for low-voltage battery operation, analog current-sense output, and comprehensive Kelvin-based fault detection - making it optimal for cost-sensitive, high-reliability automotive motor control where external supply rails are unavailable or unstable.

Availability

A3935KLQ is available at Aetrix Electronics and suitable for electric power steering, HVAC blower motors, engine cooling fans, and hybrid auxiliary compressors requiring stable component supply across extended automotive temperature ranges and long production lifecycles.

Supply support for A3935KLQ 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

Allegro MicroSystems is a U.S.-based designer of high-performance magnetic sensors and power ICs, specializing in automotive and industrial motion control solutions since 1989.

The A3935KLQ belongs to Allegro's automotive-grade 3-phase gate driver product line, engineered specifically for high-power motor control in safety-critical systems such as EPS and HVAC, with emphasis on integrated fault protection and battery-range resilience.

FAQ

What is the maximum battery voltage the A3935KLQ can withstand?

The A3935KLQ supports a load supply voltage (VBAT) range of –0.6 V to 40 V. Its absolute maximum rating is 40 V, and its VBAT overvoltage protection is adjustable from 19.4 V to 40 V using the OVSET pin. This allows safe operation during automotive load-dump transients while maintaining functional integrity up to the rated limit. The A3935KLQ remains fully operational within its specified 7 V to 40 V operating range.

Does the A3935KLQ require external bootstrap diodes?

No, the A3935KLQ integrates internal bootstrap diodes for each high-side driver channel (GHA/GHB/GHC). These diodes connect between VREG and CA/CB/CC pins, eliminating the need for external discrete diodes. The datasheet specifies forward voltage (0.8–2.0 V) and resistance (2.5–7.5 Ω) characteristics for these internal diodes, confirming their role in charging the external bootstrap capacitors during low-side conduction.

How does the A3935KLQ implement short-to-ground fault detection?

The A3935KLQ detects short-to-ground faults when a high-side MOSFET is commanded ON: it compares the voltage difference between VDRAIN and the corresponding motor phase (e.g., SA) against the VDSTH threshold. If VDRAIN – VSx exceeds VDSTH ±0.25 V, the FAULT pin asserts low. This detection only activates when GHx = 1 and ENABLE = 1, ensuring accurate Kelvin-based diagnosis without false triggers during inactive states.

Can the A3935KLQ drive both N-channel and P-channel MOSFETs?

The A3935KLQ is designed exclusively for N-channel MOSFETs in a 3-phase bridge configuration. Its high-side drivers (GHA/GHB/GHC) use bootstrap architecture to generate gate voltages above the motor phase voltage, which is necessary for N-FET enhancement-mode operation. It does not support P-channel devices, as its outputs lack negative voltage capability or complementary drive logic required for P-FET source-follower configurations.

What is the purpose of the VDRAIN pin on the A3935KLQ?

The VDRAIN pin provides a Kelvin connection to the high-side MOSFET drains, enabling accurate drain-to-source voltage monitoring independent of PCB trace resistance. When paired with VDSTH, it allows detection of open-bridge faults and short-to-ground conditions. During high-side conduction, VDRAIN–VSx is compared to VDSTH; deviation beyond ±0.25 V triggers the FAULT output. This pin must be routed as an isolated trace directly to the MOSFET drain nodes to preserve measurement fidelity.