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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - DC DC Switching Regulators

STMicroelectronics L6985FTR

Name: L6985FTR
Brand: STMicroelectronics
SKU: L6985FTR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: L6985FTR

Manufacturer:: STMicroelectronics

Category:: Voltage Regulators - DC DC Switching Regulators

Package:: 16-PowerTSSOP (0.173", 4.40mm Width)

Datasheet:: L6985FTR.pdf

Description:: IC REG BUCK ADJ 500MA 16HTSSOP

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Product details

Overview

L6985FTR from STMicroelectronics is a 38 V, 500 mA synchronous step-down switching regulator with peak-current-mode control, 30 µA quiescent current in low-consumption mode (LCM), adjustable output voltage (0.85 V to VIN), and dual operating modes (LCM/LNM) for light-load efficiency or constant-frequency low-noise operation. It integrates high-side (360 mΩ) and low-side (150 mΩ) MOSFETs and supports output voltage sequencing via open-drain RST.

For engineers reviewing the L6985FTR datasheet, L6985FTR pinout, L6985FTR application, or L6985FTR equivalent, key selection criteria include input voltage range (4–38 V), quiescent current (30 µA LCM @ 3.3 V), adjustable fSW (250 kHz–2 MHz), embedded voltage supervisor with programmable delay, and HTSSOP16 thermal performance (R_thJA = 40 °C/W).

Technical Context

The L6985FTR employs peak-current-mode architecture with pulse-by-pulse overcurrent protection, switchover-capable internal regulator (VBIAS-supported), and ratiometric soft-start. Its error amplifier features 100 dB gain and ±25 µA output drive, while the integrated sawtooth oscillator enables precise frequency setting via FSW pinstrapping.

It implements dual-mode operation: Low Noise Mode (LNM) enforces fixed-frequency PWM across full load range for EMI-sensitive applications; Low Consumption Mode (LCM) enables burst-mode operation at light loads to achieve 30 µA I_Q, with programmable skip current threshold (0.15–0.5 A) and active RST threshold selection (80–96% of V_OUT) via MLF pinstrapping.

Key Specifications

Parameter	Value and Actual Design Meaning
Input Voltage Range	4 V to 38 V - supports 5 V, 12 V, and 24 V industrial bus systems without external pre-regulation.
Output Current	0.5 A DC - sufficient for powering microcontrollers, sensors, and FPGA I/O rails in compact designs.
Quiescent Current (LCM)	30 µA at light load (V_OUT = 3.3 V) - enables battery-backed or energy-harvesting systems with multi-year standby life.
Switching Frequency	Adjustable 250 kHz to 2 MHz via resistor strapping - allows optimization of size (high f_SW) vs. efficiency (low f_SW) and EMI compliance.
R_DS(on) HS / LS	360 mΩ / 150 mΩ - reduces conduction losses and thermal stress, enabling high efficiency (>90%) at medium-to-heavy loads.
Output Voltage Range	0.85 V to VIN - supports direct regulation from 3.3 V, 5 V, or 12 V rails down to core logic voltages (e.g., 1.2 V, 1.8 V).
Voltage Supervisor	Programmable RST threshold (80–96% V_OUT) with adjustable delay - provides reliable power-good signaling and controlled sequencing for µC/FPGA reset timing.
Shutdown Current	8 µA typical - ensures minimal system leakage during deep sleep or fault shutdown.

Pinout & Package

Package: HTSSOP16 (exposed pad), R_thJA = 40 °C/W, R_thJC = 5 °C/W. Exposed pad must be connected to SGND/PGND for thermal and electrical integrity.

Pin/Terminal	Circuit Role	Design Meaning
1 RST	Open-collector reset output	Asserts low when V_FB falls below programmed threshold; delay set by external capacitor on DELAY pin for sequencing.
2 VCC	Internal analog supply rail	Requires ≥470 nF ceramic decoupling; powers bandgap reference and error amplifier.
3 SS/INH	Soft-start ramp / inhibit input	Charged by internal 4 µA current source; clamp to GND disables regulator; controls startup inrush.
4 SYNCH/ISKP	Sync input / skip current select	In LNM: accepts external clock; in LCM: selects skip threshold via pull-up/down resistor.
5 FSW	Frequency selection strap	Resistor divider to VCC/GND sets f_SW (250 kHz–2 MHz); configuration locked before soft-start completion.
6 MLF	Mode and RST threshold select	Straps LNM/LCM mode and RST activation point (80–96% V_OUT) via resistor network.
7 COMP	Error amplifier output	Connects to compensation network (RC + C); drives internal PWM comparator with 100 dB gain and ±25 µA drive.
8 DELAY	RST assertion delay timing	External capacitor sets delay time after V_OUT exceeds threshold; floating = immediate RST release (Power Good).
9 FB	Feedback input	Inverting input of transconductance error amplifier; senses V_OUT via resistive divider (V_REF = 0.85 V).
10 SGND	Signal ground reference	Reference for analog blocks (error amp, reference, comparators); separate from PGND to reduce noise coupling.
11,12 PGND	Power ground return	High-current return path for LX switches; must be low-inductance connection to minimize switching noise.
13,14 LX	Switch node	Connects to external inductor; carries high di/dt; requires tight layout and Kelvin connection to PGND.
15 VIN	Main input supply	Accepts 4–38 V; requires bulk and high-frequency input capacitors near PGND/VIN pins.
16 VBIAS	Switchover auxiliary supply	Connect to regulated output (3–5.5 V) to reduce I_Q at VIN; internal switchover threshold ~3.0 V.

Key Features

Feature	Design Value
Peak-current-mode control	Enables fast transient response and inherent cycle-by-cycle overcurrent protection without external sense resistor.
Dual operating modes (LCM/LNM)	LCM maximizes light-load efficiency (30 µA I_Q); LNM guarantees fixed-frequency operation for predictable EMI filtering.
Embedded voltage supervisor with RST	Provides programmable reset assertion and sequencing delay-eliminates need for external supervisor IC in µC/FPGA systems.
Synchronization capability	Supports master/slave configuration in LNM and external clock sync up to 2 MHz-enables multi-rail coherent switching.
Switchover internal regulator	Draws bias current from VBIAS (e.g., 3.3 V output) instead of VIN, reducing effective I_Q and improving system-level efficiency.
Thermal shutdown with hysteresis	Triggers at 165 °C with 30 °C hysteresis-prevents thermal runaway while allowing safe recovery without cycling.

Applications

Industrial PLC Power Rails

Low-Noise Sensor Signal Conditioning

Use Scenario: Powering 3.3 V I/O and communication interfaces in DIN-rail mounted programmable logic controllers operating from 24 V DC bus.

IC Role / Device Role / Timing Role: Primary buck converter delivering regulated 3.3 V with sequencing-controlled reset to ensure deterministic µC boot after brownout recovery.

Use Value: 4–38 V input range eliminates need for upstream pre-regulator; 30 µA LCM I_Q extends backup battery life during maintenance mode.

Use Scenario: Supplying ultra-low-noise analog front-end (AFE) circuits for precision temperature/pressure sensors in factory automation.

IC Role / Device Role / Timing Role: Fixed-frequency LNM operation minimizes switching ripple injection into sensitive analog signal paths.

Use Value: Constant 2 MHz f_SW enables use of small ceramic capacitors and simple LC filters; R_DS(on) values limit thermal drift in sealed enclosures.

Decentralized Intelligent Node (DIN)

FPGA Core & I/O Rail Sequencing

Use Scenario: Compact remote I/O modules requiring multiple regulated rails (e.g., 1.2 V core, 3.3 V I/O) powered from 12 V field bus.

IC Role / Device Role / Timing Role: Single-rail buck supplying 3.3 V with RST-driven sequencing to coordinate startup of auxiliary LDOs or secondary converters.

Use Value: Programmable RST delay (via DELAY capacitor) ensures proper power-up order without external timers or CPLDs.

Use Scenario: Powering Xilinx Artix-7 FPGA banks requiring strict voltage ramp timing and reset assertion relative to V_CCINT/V_CCO.

IC Role / Device Role / Timing Role: Generates precise 3.3 V I/O rail with RST output synchronized to V_OUT stabilization for FPGA PROG_B coordination.

Use Value: Embedded supervisor eliminates discrete reset IC; 0.85 V feedback reference enables accurate scaling for diverse FPGA voltage requirements.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
LM61480RGER	Higher 8 A rating, 2.7–18 V input, 15 µA I_Q, no RST output or VBIAS switchover	Better suited for high-current, wide-temp automotive applications; lacks sequencing and low-noise mode	Select when >0.5 A output or AEC-Q100 qualification is required; not drop-in for L6985FTR's industrial sequencing use cases
TPS62865ARGRR	6 A, 2.7–6 V input, 2.5 µA I_Q, integrated PMBus, no HTSSOP package or 38 V rating	Targets low-voltage compute rails; lacks high-voltage tolerance and industrial-grade thermal specs	Prefer for battery-powered sub-6 V systems needing digital control; incompatible with 12/24 V bus inputs

Compared with LM61480RGER and TPS62865ARGRR, the L6985FTR uniquely balances 38 V input tolerance, 30 µA LCM quiescent current, programmable RST sequencing, and HTSSOP16 thermal performance-making it optimal for space-constrained, multi-rail industrial nodes where voltage supervision and bus compatibility are critical.

Availability

L6985FTR is available at Aetrix Electronics and suitable for industrial PLCs, decentralized intelligent nodes, sensor signal conditioning circuits, and FPGA I/O rail sequencing requiring stable component supply across extended temperature and long product lifecycles.

Supply support for L6985FTR 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 specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer applications.

The L6985FTR belongs to ST's high-voltage synchronous buck regulator product line, designed specifically for robust, low-quiescent-current DC-DC conversion in 12 V and 24 V industrial bus environments with built-in supervision and sequencing.

FAQ

What is the maximum allowable input voltage for L6985FTR, and what protection prevents damage above this limit?

The absolute maximum input voltage is 40 V, with recommended continuous operation up to 38 V. Internal overvoltage protection (OVP) triggers at 1.15×V_REF (≈0.97 V) on the FB pin, causing the controller to discharge the output capacitor through the low-side MOSFET. This protects downstream loads during input transients or feedback loop failure, independent of UVLO thresholds on VCC or VIN.

How does the VBIAS switchover feature reduce total system quiescent current?

VBIAS connects to the regulated output (e.g., 3.3 V). When VBIAS is between 3 V and 5.5 V, the internal regulator switches its bias current source from VIN to VBIAS, reducing the effective I_Q drawn from the main input. At V_OUT = 3.3 V, this cuts VIN-referred I_Q from ~70 µA (no switchover) to ~30 µA (with switchover), directly extending battery runtime in always-on systems.

Can L6985FTR synchronize to an external clock in Low Consumption Mode (LCM)?

No-synchronization is only supported in Low Noise Mode (LNM). In LCM, the SYNCH/ISKP pin functions as ISKP (skip current level select), configured via resistor strapping. Attempting external clock injection in LCM will not lock the switching frequency and may cause erratic operation due to burst-mode timing conflicts.

What is the minimum recommended soft-start capacitor value, and how does it affect startup behavior?

The minimum CSS is determined by Equation 1: CSS = (T_SS × 4 µA × 3) / 0.85 V. For a 10 ms soft-start, CSS ≈ 141 nF. Using too small a capacitor risks insufficient ramp time, causing excessive inrush current and potential thermal stress on external components. The device discharges CSS at 0.6 mA for ≤1 ms after fault events, so CSS > 67 nF is recommended to ensure full discharge and reliable restart.

L6985FTR Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: 16-PowerTSSOP (0.173", 4.40mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Active

Function:: Step-Down

Output Configuration:: Positive

Topology:: Buck

Output Type:: Adjustable

Number of Outputs:: 1

Voltage - Input (Min):: 4V

Voltage - Input (Max):: 38V

Voltage - Output (Min/Fixed):: 0.85V

Voltage - Output (Max):: 38V

Current - Output:: 500mA

Frequency - Switching:: 250kHz ~ 2MHz

Synchronous Rectifier:: Yes

Operating Temperature:: -40°C ~ 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-HTSSOP

L6985FTR FAQ

1.How can I place an order for L6985FTR through Aetrix?

Please submit a Request for Quotation (RFQ) for L6985FTR on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for L6985FTR reliable?

The price and inventory of L6985FTR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for L6985FTR is usually 5 days.

3.What payment methods are accepted for L6985FTR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for L6985FTR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for L6985FTR?

L6985FTR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your L6985FTR order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for L6985FTR?

For technical support, including L6985FTR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your L6985FTR requirements.

6.How does Aetrix verify that L6985FTR is sourced from the original manufacturer or authorized distributors?

All L6985FTR products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that L6985FTR meets industry standards.

7.What is the process for return or replacement of L6985FTR?

All L6985FTR units undergo pre-shipment inspection (PSI). If there is an issue with L6985FTR, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The L6985FTR part is unused and in its original packaging.

Return procedure for L6985FTR:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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