STMicroelectronics L7986TATR

Overview

L7986TATR from STMicroelectronics is a 3 A synchronous step-down DC-DC switching regulator with integrated P-channel MOSFET, designed for high-input-voltage industrial and automotive 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 100% duty cycle for low-dropout operation - used in car infotainment power supplies and FPGA core voltage regulation.

For engineers reviewing the L7986TATR datasheet, L7986TATR pinout, L7986TATR application, or L7986TATR equivalent, key selection criteria include input voltage range (4.5–38 V), guaranteed 3 A load capability, HSOP8 thermal performance (R_thJA = 40 °C/W), voltage-mode control architecture, and synchronization capability for multi-rail phase interleaving.

Technical Context

The L7986TATR implements voltage-mode PWM control with feed-forward compensation: input voltage variation modulates sawtooth slope to maintain constant PWM gain, while external resistor on FSW pin adjusts oscillator frequency up to 1 MHz. Its block diagram includes an integrated 0.6 V reference, error amplifier with COMP pin access, peak-current-limited P-channel MOSFET driver, and hysteretic thermal shutdown at 150 °C with 30 °C hysteresis.

Synchronization is implemented via the SYNCH pin: when floating, it outputs a 180° phase-shifted clock; when tied to another L7986TATR or external source, it enables master-slave interleaving with half-cycle phase offset. Soft-start uses a 64-step staircase ramp (9.5 mV/step) on the error amplifier's non-inverting input, yielding 7.4–9.7 ms startup time depending on FSW setting.

Key Specifications

Pinout & Package

Package: HSOP8 with exposed thermal pad (pin 0), RoHS-compliant, moisture sensitivity level 3. Exposed pad must be soldered to PCB thermal plane for R_thJA = 40 °C/W performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM5164QPWPRQ1 and MP2451DT-LF-Z, the L7986TATR uniquely combines 3 A output, 38 V input, adjustable 0.6 V reference, and SYNCH capability - making it the only option among the three suitable for automotive FPGA core supplies requiring phase interleaving and wide VIN tolerance.

Availability

L7986TATR is available at Aetrix Electronics and suitable for automotive infotainment systems, industrial FPGA power supplies, DSL modem DC-DC modules, and LED bias applications requiring stable component supply across extended temperature and long production lifecycles.

Supply support for L7986TATR 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 power management, microcontrollers, and automotive-grade analog ICs.

The L7986TATR belongs to ST's high-voltage buck regulator product line, engineered for robust operation in harsh environments - specifically targeting automotive and industrial applications where wide input range, thermal resilience, and functional safety readiness are essential.

FAQ

What is the minimum recommended input capacitance for L7986TATR at 38 V input and 3 A output?

For 38 V input and 3 A output at 250 kHz, the minimum ceramic input capacitance is 22 µF (X7R, 50 V rated), placed directly between VCC and GND pins. This value ensures peak-to-peak ripple remains below 1% of VINMAX and handles RMS input current up to 1.5 A. Use multiple parallel 10 µF/0805 capacitors with short, low-inductance traces to ground plane.

Can L7986TATR operate with an output voltage equal to input voltage?

Yes - L7986TATR supports 100% duty cycle operation, allowing V_OUT = V_IN when input voltage drops near the desired output (e.g., 5 V output with 5.5 V input). In this mode, the internal P-channel MOSFET remains fully enhanced, acting as a low-loss pass element with R_DS(on) ≈ 300 mΩ, enabling graceful brown-out recovery without output collapse.

How does the SYNCH pin behave when left floating versus externally driven?

When floating, SYNCH outputs a 180° phase-shifted version of the internal clock - useful for interleaving two L7986TATR devices. When driven by an external TTL/CMOS clock >250 kHz, it synchronizes the device to that frequency with zero phase delay. The pin tolerates 0–3.3 V logic levels and sinks up to 1 mA in slave mode, ensuring reliable multi-chip timing alignment.

Is external compensation mandatory for stable operation?

Yes - the COMP pin requires an external Type II or Type III compensation network connected between COMP, FB, and GND. The choice depends on output capacitor ESR: Type II suffices for high-ESR electrolytics; Type III is required for low-ESR ceramics to ensure ≥45° phase margin across line, load, and temperature. ST provides design equations and example values in Section 6.4 of the datasheet.