STMicroelectronics L7985

Overview

L7985 from STMicroelectronics is a 2 A step-down switching regulator with integrated P-channel MOSFET, designed as the main DC-DC power stage in mid-power embedded systems. It operates from 4.5 V to 38 V input, delivers adjustable output from 0.6 V, features 250 kHz base switching frequency (programmable up to 1 MHz), and supports 100% duty cycle for low-dropout operation - used in FPGA core supply rails and LCD TV main power rails.

For engineers reviewing the L7985 datasheet, L7985 pinout, L7985 application, or L7985 equivalent, this device requires attention to its voltage-mode control architecture, SYNCH pin phase-shift synchronization capability, soft-start timing dependency on FSW, thermal resistance differences between VFDFPN (60 °C/W) and HSOP (40 °C/W) packages, and FB pin's fixed 0.6 V reference for output regulation.

Technical Context

The L7985 implements voltage-mode PWM control using an internal 0.6 V reference and sawtooth oscillator whose slope is modulated by both input voltage (voltage feed-forward) and switching frequency (frequency feed-forward) to maintain constant PWM gain. Its error amplifier provides 100 dB DC gain and 4.5 MHz GBWP, with COMP pin enabling Type II or Type III compensation based on output capacitor ESR.

Overcurrent protection uses blanking-time–gated peak-current sensing with pulse-skipping down to 1/8 nominal frequency under sustained overload; thermal shutdown activates at 150 °C with 30 °C hysteresis and restarts at ~120 °C. The EN pin enables logic-level (0.3 V / 1.2 V thresholds) and VCC-compatible standby control with <30 µA quiescent current.

Key Specifications

Pinout & Package

Available in VFDFPN10 (3 × 3 × 1.0 mm, exposed pad) and HSOP8 (exposed pad) packages. Both feature thermal pads for enhanced heat dissipation.

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 L7985 uniquely delivers 2 A output with programmable frequency, master/slave synchronization, and 100% duty cycle - making it the only option among the three suitable for FPGA core and LCD TV main rail applications requiring >1.5 A continuous current and thermal robustness.

Availability

L7985 is available at Aetrix Electronics and suitable for FPGA core supply, LCD TV main power rail, DSL modem power management, and industrial PLC I/O module supply requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for L7985 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

The L7985 belongs to ST's high-voltage buck regulator product line, engineered for robust, integrated DC-DC conversion in space- and thermal-constrained applications where reliability across wide input ranges is essential.

FAQ

What is the minimum output voltage achievable with the L7985?

The L7985 regulates output voltage starting from 0.6 V - its internal feedback reference voltage. This value is fixed and specified as 0.593 V to 0.607 V over temperature and line conditions. To achieve exactly 0.6 V, connect the FB pin directly to the output; any higher voltage requires a resistor divider scaling the output down to 0.6 V at FB.

Can the L7985 synchronize with an external clock source?

Yes - the SYNCH pin accepts external clock signals between 210 kHz and 1 MHz. When driven externally, the device synchronizes with zero phase shift and adjusts its internal sawtooth amplitude, which affects PWM gain. For stable loop performance, pre-adjust the free-running frequency using the FSW resistor to be slightly lower than the external clock frequency.

How does the soft-start time vary with switching frequency?

Soft-start time is inversely proportional to switching frequency: T_SS = 2048 / F_SW. At 250 kHz, it is 8.2 ms; at 1 MHz, it reduces to 2.05 ms. This occurs because the internal 64-step staircase ramp advances one step every 32 clock cycles - so higher F_SW shortens total ramp duration.

What thermal considerations differentiate the VFDFPN and HSOP packages?

The HSOP8 package achieves θ_JA = 40 °C/W due to its larger exposed pad and leadframe geometry, enabling ~50% higher power dissipation than VFDFPN (60 °C/W) at the same ambient temperature. Layout must maximize copper area under the exposed pad and use ≥6 thermal vias for both packages to realize rated thermal performance.