STMicroelectronics L7985ATR

Overview

L7985ATR from STMicroelectronics is a 2 A step-down switching regulator with integrated P-channel MOSFET, designed for high-efficiency DC-DC conversion in space-constrained industrial and consumer power rails. It operates from 4.5 V to 38 V input, delivers adjustable output down to 0.6 V, features 250 kHz–1 MHz programmable switching frequency, internal soft-start, and supports zero-load operation - used in FPGA core supplies and LCD TV main power stages.

For engineers reviewing the L7985ATR datasheet, L7985ATR pinout, L7985ATR application, or L7985ATR equivalent, key selection criteria include its 2.5 A current limit, voltage feed-forward architecture, thermal shutdown at 150 °C, and dual-package availability (VFDFPN10 and HSOP8) with exposed thermal pads.

Technical Context

The L7985ATR implements voltage-mode PWM control with a fixed-frequency sawtooth oscillator whose slope is dynamically adjusted via voltage and frequency feed-forward to maintain constant loop gain across input voltage and switching frequency variations. Its error amplifier has 100 dB DC gain and 4.5 MHz GBWP, driving a COMP pin for external Type II or Type III compensation networks.

Overcurrent protection uses blanking-time–gated peak-current sensing (200 ns masking), enabling pulse-skipping down to 1/8 nominal frequency under overload. Thermal shutdown activates at 150 °C with 30 °C hysteresis, and the EN pin provides active-high enable with 1.2 V threshold and internal pull-down.

Key Specifications

Pinout & Package

Available in VFDFPN10 (3 × 3 × 1.0 mm, exposed thermal pad) and HSOP8 (exposed pad), both optimized for low thermal resistance (60 °C/W and 40 °C/W respectively).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5164QDRCRQ1 and MP2451DT-LF-Z, the L7985ATR uniquely combines 2 A capability, voltage feed-forward, zero-load stability, and dual-package thermal optimization - making it the only suitable choice for FPGA core rails and industrial 24 V-to-12 V conversion where reliability and transient performance are critical.

Availability

L7985ATR is available at Aetrix Electronics and suitable for FPGA power delivery, LCD TV main rails, DSL modem DC-DC modules, and industrial PLC I/O supplies requiring stable component supply across extended temperature and long production lifecycles.

Supply support for L7985ATR 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, designing and manufacturing analog, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The L7985ATR belongs to ST's high-voltage buck regulator product line, engineered specifically for robust, high-current DC-DC conversion in harsh environments - emphasizing thermal resilience, wide VIN range, and transient immunity for industrial and broadcast equipment.

FAQ

What is the maximum achievable output current for L7985ATR in HSOP8 package at 60 °C ambient?

At 60 °C ambient, the HSOP8 package's R_thJA of 40 °C/W allows a maximum power dissipation of 2 W before reaching 150 °C junction temperature. With typical 200 mΩ R_DS(on) and 12 V input → 3.3 V output, conduction loss dominates: P_LOSS ≈ I² × 0.2 Ω. Solving I² × 0.2 ≤ 2 gives I ≤ ~3.16 A - but the device is rated for 2 A continuous due to combined conduction, switching, and gate drive losses. Derating to 2 A ensures margin across all conditions.

Can L7985ATR operate with input voltage below 4.5 V?

No. The absolute maximum ratings specify V_CC ON threshold at 4.5 V, and UVLO hysteresis begins at that point. Below 4.5 V, the internal bias circuitry cannot sustain regulation, and the device remains disabled. Attempting operation below this voltage risks unstable startup, erratic switching, or failure to regulate - it is outside the validated operating range per ST's production data.

How does the SYNCH pin behave when left floating?

When floating, the SYNCH pin outputs a square wave synchronized to the internal oscillator with 180° phase shift relative to the power switch turn-on. This enables natural interleaving when two L7985ATR devices share the same SYNCH net - one acts as master (higher frequency), the other as slave (phase-shifted), reducing input capacitor RMS current without external clock generation.

Is external compensation mandatory for stable operation?

Yes. The COMP pin is the error amplifier output and requires an external Type II or Type III network connected between COMP, FB, and GND. ST's datasheet specifies exact resistor/capacitor values based on output capacitor ESR and switching frequency. Omitting compensation causes instability, oscillation, or poor transient response - no internal compensation is provided.