STMicroelectronics L5985TR

Overview

L5985TR from STMicroelectronics is a 2 A synchronous step-down DC-DC switching regulator with integrated P-channel MOSFET, operating from 2.9 V to 18 V input and delivering adjustable output down to 0.6 V. It features 250 kHz base switching frequency (programmable up to 1 MHz), internal soft-start, 100% duty-cycle low-dropout operation, and overcurrent/thermal protection - deployed in LCD TV power rails, FPGA core supplies, and XDSL line cards.

For engineers reviewing the L5985TR datasheet, L5985TR pinout, L5985TR application, or L5985TR equivalent, key selection criteria include input voltage range (2.9–18 V), output adjustability (0.6 V min), thermal resistance (60 °C/W), VFQFPN8 package footprint, and synchronization capability via SYNCH pin for multi-rail phase interleaving.

Technical Context

The L5985TR implements voltage-mode PWM control with feedforward compensation: input voltage and switching frequency modulate sawtooth slope to maintain constant PWM gain across line and frequency variations. Its error amplifier has 100 dB DC gain, 4.5 MHz GBWP, and rail-to-rail COMP output swing (0–3.3 V) for robust loop stability with Type II or III networks.

Functional blocks include a programmable oscillator (250 kHz–1 MHz), peak-current-limited P-channel MOSFET driver (R_DS(on) = 140–220 mΩ), 0.6 V reference-based feedback comparator, and hiccup-mode overcurrent protection triggered at 2.5–3.3 A. Thermal shutdown activates at 150 °C with 30 °C hysteresis, and INH enables logic-controlled standby (<30 µA quiescent).

Key Specifications

Pinout & Package

VFQFPN8 3 mm × 3 mm package with exposed thermal pad (pin 1 marked by dot); RoHS-compliant, halogen-free, and qualified for industrial temperature range (−40 °C to +125 °C junction).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315DJ-LF-Z and TPS54202DRCT, the L5985TR uniquely supports 2.9 V start-up, 100% duty cycle, and synchronization for multi-phase designs - making it optimal for space-constrained, multi-rail consumer electronics with mixed 3.3 V/1.2 V/0.9 V domains.

Availability

L5985TR is available at Aetrix Electronics and suitable for LCD TV power management, FPGA core supplies, and XDSL line card DC-DC conversion requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant VFQFPN packaging.

Supply support for L5985TR 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, designing and manufacturing analog, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

The L5985TR belongs to ST's high-efficiency monolithic DC-DC regulator product line, engineered specifically for compact, cost-sensitive point-of-load applications in set-top boxes, displays, and networking equipment where thermal performance and input voltage flexibility are critical.

FAQ

What is the minimum input voltage required for L5985TR startup?

The L5985TR requires a minimum input voltage of 2.9 V to initiate regulation, verified by its V_CCON turn-on threshold specification. Below this level, the UVLO circuit holds the device in shutdown, preventing erratic operation. This allows direct use on 3.3 V intermediate buses without pre-regulation.

Can L5985TR operate with 0 A load current while maintaining regulation?

Yes - the L5985TR supports zero-load current operation per datasheet Section 4. Functional Description. Its voltage-mode control architecture and low-quiescent-current design (20–30 µA in standby) ensure stable 0.6 V reference tracking and output regulation even with no output capacitance load.

How does the SYNCH pin enable phase interleaving between two L5985TR devices?

When SYNCH pins of two L5985TR units are connected, the higher-frequency device becomes master and forces the lower-frequency unit into slave mode with 180° phase shift. This halves RMS input capacitor current, reducing heating and EMI - confirmed in Figure 4 and Section 4.1 of the official datasheet.

What is the maximum allowable thermal resistance for reliable 2 A operation at 70 °C ambient?

With R_thJA = 60 °C/W and maximum junction temperature of 150 °C, the L5985TR dissipates up to 1.33 W at 70 °C ambient (ΔT = 80 °C). At 2 A output and 12 V input → 3.3 V output (η ≈ 88%), power dissipation is ~1.1 W - within safe margin, provided PCB copper area matches ST's demo board layout.