STMicroelectronics A7985A

Overview

A7985A from STMicroelectronics is a voltage-mode step-down switching regulator with integrated 2.5 A P-channel high-side MOSFET, designed for automotive power conversion. It delivers up to 2 A DC output current across 4.5 V–38 V input range, supports adjustable output from 0.6 V, operates at 250 kHz (programmable to 1 MHz), and features AEC-Q100 qualification, internal soft-start, and 100% duty-cycle low-dropout operation - used in automotive LED driving systems.

For engineers reviewing the A7985A datasheet, A7985A pinout, A7985A application, or A7985A equivalent, this page provides verified technical context on its voltage feed-forward architecture, HSOP8 thermal performance (R_th(JA) = 40 °C/W), overcurrent/thermal protection behavior, and synchronization capability for multi-phase automotive power rails.

Technical Context

The A7985A implements voltage-mode control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage feed-forward (input-dependent ramp scaling) and frequency feed-forward (FSW-resistor–dependent ramp scaling) to maintain constant PWM gain across line and frequency variations. Its error amplifier features 100 dB open-loop gain and rail-to-rail COMP output drive (19 mA source / 30 mA sink).

Synchronization is achieved through the SYNCH pin, supporting master/slave phase-shifted operation (180° offset) when pins are tied together, or external clock locking with amplitude-modulated sawtooth truncation. The embedded P-channel MOSFET has R_DS(on) = 200–400 mΩ and peak current limit of 2.5–3.5 A, enabling robust short-circuit handling without external sensing.

Key Specifications

Pinout & Package

Package: HSOP8 with exposed thermal pad (mechanical outline per Table 10, DocID023128 Rev 8). Exposed pad must be soldered to PCB ground plane for optimal thermal performance (R_th(JA) = 40 °C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down regulator applications.

Compared with LM5164QPWPRQ1 and TPS54240QDGQRQ1, the A7985A uniquely combines AEC-Q100 qualification, voltage-mode feed-forward, 100% duty cycle, and built-in SYNCH for multi-phase automotive rails - making it optimal for thermally constrained, safety-critical LED and ADAS power stages where transient immunity and thermal predictability are paramount.

Availability

A7985A is available at Aetrix Electronics and suitable for automotive LED driving, infotainment system power rails, and ADAS camera modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for A7985A 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive-grade analog, power, and microcontroller solutions with broad AEC-Q100 product coverage.

The A7985A belongs to ST's automotive power management portfolio, engineered specifically for high-reliability, thermally demanding vehicle subsystems such as lighting, ADAS, and body electronics - emphasizing robustness under load-dump, cold-crank, and extended ambient temperature extremes.

FAQ

What is the maximum output current the A7985A can deliver continuously?

The A7985A guarantees ≥2.5 A peak switch current and is rated for up to 2 A continuous DC output current under typical conditions: T_A ≤ 60 °C, HSOP8 mounted on standard demo board with exposed pad soldered to ground plane, and proper input/output capacitors. Actual achievable current depends on ambient temperature, PCB copper area, and input-output voltage differential - see Figure 22–24 for junction temperature vs. I_OUT curves at 5 V, 12 V, and 24 V input.

Does the A7985A support synchronization with external clock sources?

Yes - the SYNCH pin supports both master/slave interleaving and external clock synchronization. When left floating, it outputs a 180° phase-shifted copy of the internal oscillator. When driven by an external clock above the internal frequency, the device locks to that clock with zero phase shift. For stable loop behavior, ST recommends pre-setting the free-running frequency within ±10% of the target sync frequency using the FSW resistor to minimize sawtooth truncation effects.

How does the voltage feed-forward function improve transient response?

Voltage feed-forward dynamically adjusts the sawtooth ramp slope in proportion to V_IN, keeping the PWM gain (duty cycle change per error voltage change) constant across input voltage variations. This eliminates gain variation during line transients - such as battery voltage sag during engine cranking - resulting in tighter output regulation and faster recovery from load steps without requiring complex adaptive compensation.

Can the A7985A operate with no load?

Yes - the A7985A is explicitly characterized for zero-load operation and maintains stable regulation down to 0 A output current. This is enabled by its voltage-mode architecture, low quiescent current (20–30 µA in standby), and absence of minimum load requirements. It is suitable for automotive always-on domains like CAN gateways or alarm systems where standby power must remain active without dummy loads.