STMicroelectronics L9857-TR-LF

Overview

L9857-TR-LF from STMicroelectronics is a high-voltage, non-inverting high-side gate driver IC designed to control N-channel PowerMOS transistors in off-line applications. It supports up to 450 V rail voltage, delivers ±500 mA peak source/sink current, achieves 100 ns rise/fall times with 2.5 nF load, and features CMOS/TTL Schmitt-trigger inputs with hysteresis. It is used in industrial AC motor drives and solid-state relay modules where robust dV/dt immunity and floating high-side operation are required.

For engineers reviewing the L9857-TR-LF datasheet, L9857-TR-LF pinout, L9857-TR-LF application, or L9857-TR-LF equivalent, key selection criteria include its 450 V high-side capability, ±50 V/ns dV/dt immunity across –40 °C to +125 °C, under-voltage lockout thresholds (7.2–9.6 V for VCC/VBS), SO-8 package thermal resistance (150 °C/W), and active-low RESET- input with 3.8 kΩ pull-up compatibility.

Technical Context

The L9857 integrates dual level shifters ("ON" and "OFF"), break-before-make logic, and pulse filters to ensure safe high-side switching. Its floating high-side section operates with VB referenced to VS, enabling direct drive of N-MOSFETs in half-bridge topologies without bootstrap capacitors.

It implements independent undervoltage lockout on both VCC and VBS rails with 0.02–0.4 V hysteresis and sub-20 ps response time. The RESET- input is actively pulled down internally and requires external 3.8 kΩ pull-up to 5 V for reliable disable functionality during power sequencing or fault conditions.

Key Specifications

Pinout & Package

Supplied in an industry-standard SO-8 package (ECOPACK® compliant, RoHS-compliant lead-free finish), the L9857-TR-LF uses a surface-mount 8-pin layout with exposed pad not present. Pin 5 is NC (no bondwire); all other pins serve defined circuit functions.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-side gate driver applications.

Compared with IR2110PbF and UCC27531DR, the L9857-TR-LF uniquely combines 450 V high-side capability, integrated dual UVLO, active-low RESET- with internal pull-down, and SO-8 simplicity-making it optimal for cost-sensitive, space-constrained industrial off-line systems requiring robustness without external support components.

Availability

L9857-TR-LF is available at Aetrix Electronics and suitable for industrial AC motor drives, solid-state relay modules, induction heating inverters, and UPS half-bridge stages requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for L9857-TR-LF 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 automotive, industrial, and power discrete solutions with strong analog/mixed-signal IP.

The L9857 belongs to ST's high-voltage gate driver product line, engineered specifically for robust, self-contained high-side switching in off-line industrial power conversion-emphasizing dV/dt immunity, integrated protection, and ease of integration in space-constrained designs.

FAQ

What is the function of the NC pin (Pin 5) on the L9857-TR-LF?

Pin 5 is a no-connect terminal with no internal bondwire or silicon connection. It must remain unconnected in PCB layout to prevent unintended coupling or leakage paths. ST specifies this pin as NC in the mechanical drawing and pin function table; routing traces or placing vias to this pad violates the device's validated design and may compromise dV/dt immunity or thermal performance.

Can the L9857-TR-LF drive a P-channel MOSFET in high-side configuration?

No-the L9857-TR-LF is explicitly designed for N-channel MOSFETs only. Its output stage architecture, level-shifting topology, and non-inverting logic assume the load is connected between VB and the MOSFET drain, with source tied to VS. Driving a P-channel device would require inverted logic polarity, different voltage referencing, and incompatible gate drive voltage swing relative to source-none of which are supported by the internal circuitry.

How does the RESET- pin behave during power-up sequencing?

The RESET- pin is internally pulled down, ensuring HO remains low until a valid logic-high signal (≥3.5 V) is applied. During VCC ramp-up, the internal UVLO holds the output disabled until VCC exceeds 7.2 V; similarly, VBS must exceed 7.2 V before the high-side stage activates. This dual-rail dependency guarantees fail-safe behavior even if RESET- floats or rises before VBS stabilizes.

Is the L9857-TR-LF qualified for automotive applications?

No-ST explicitly states in the datasheet disclaimer that the L9857 is not designed or authorized for automotive, safety-critical, or aerospace applications. It lacks AEC-Q100 qualification, automotive-grade temperature screening, and functional safety documentation. For automotive use, ST recommends alternatives like the L9301 or ISO-certified gate drivers with ASIL compliance and extended qualification testing.