STMicroelectronics VIPER35LDTR

Overview

VIPER35LDTR from STMicroelectronics is a quasi-resonant high-voltage offline converter IC integrating an 800 V avalanche-rugged power MOSFET, built-in HV start-up, soft-start, and multifunction ZCD pin for zero-current detection, OCP threshold setup, output OVP, and feed-forward compensation. It supports isolated flyback topology with optocoupler feedback and delivers up to 22 W in open-frame designs at 50 °C ambient.

For engineers reviewing the VIPER35LDTR datasheet, VIPER35LDTR pinout, VIPER35LDTR application, or VIPER35LDTR equivalent, key selection criteria include its 136 kHz frequency limit (L-type), <30 mW no-load consumption at 230 VAC, brown-out hysteresis control, thermal shutdown with 30 °C hysteresis, and integrated senseFET current sensing for lossless protection.

Technical Context

The VIPER35LDTR implements a current-mode PWM controller with valley-synchronized quasi-resonant (QR) operation, using ZCD pin detection to trigger MOSFET turn-on at transformer demagnetization zero-crossing. Its internal oscillator enforces a hard 136 kHz frequency clamp to minimize EMI and enable compact filter design.

Brown-out protection uses a resistor-divider input (BR pin) with 0.45 V threshold and 50 mV hysteresis, enabling independent switch-on/switch-off thresholds. Protection logic includes auto-restart short-circuit response, output overvoltage detection via ZCD-based resistor divider, and hysteretic thermal shutdown at 155 °C nominal.

Key Specifications

Pinout & Package

Package: SO-16 narrow (SO 16 N), surface-mount, with pins 13–16 internally connected to the metal drain frame for enhanced thermal dissipation and high-voltage isolation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quasi-resonant offline converter applications.

Compared with ICE3B0565J and LNK3206D, VIPER35LDTR provides higher voltage ruggedness (800 V), superior light-load efficiency via burst mode, and unified ZCD functionality-making it optimal for 15–22 W adapters requiring regulatory compliance and robust protection.

Availability

VIPER35LDTR is available at Aetrix Electronics and suitable for USB-C adapters, smart home power supplies, industrial sensor transmitters, and white goods auxiliary rails requiring stable component supply and long-term lifecycle support.

Supply support for VIPER35LDTR 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 analog ICs for industrial, automotive, and consumer markets.

VIPER35LDTR belongs to ST's VIPer™ family of high-voltage offline converters-designed specifically for cost-sensitive, high-efficiency AC-DC power supplies up to 25 W with minimal external components and full protection integration.

FAQ

What is the difference between VIPER35LDTR and VIPER35HDTR?

The 'L' and 'H' suffixes denote different quasi-resonant frequency limits: VIPER35LDTR is rated for 136 kHz max, optimized for EMI filter minimization and lower transformer core losses; VIPER35HDTR supports up to 225 kHz, enabling smaller magnetics and extended QR range at medium loads. Both share identical pinout, protection features, and SO-16 packaging.

Can VIPER35LDTR operate without an auxiliary winding?

Yes-its embedded HV start-up circuit draws charging current directly from the DRAIN pin during power-up, eliminating the need for an auxiliary winding to charge VDD. However, an auxiliary winding is still required for sustained operation once VDD drops below the UVLO threshold, unless an external bias supply is used.

How is output overvoltage protection implemented?

OVP is implemented via the ZCD pin using an external resistor divider (ROVP/RLIM) that scales the auxiliary winding voltage. When the scaled voltage exceeds 4.2 V (typ.), the IC triggers auto-restart protection. This method avoids secondary-side optocoupler dependency for OVP, improving reliability and reducing component count.

What thermal derating applies to VIPER35LDTR in SO-16 package?

With standard FR4 PCB (100 mm² copper pour), RthJA is 80 °C/W. At 230 VAC and 22 W output, junction temperature rise is ~1.5 W × 80 °C/W = 120 °C above ambient. For continuous 50 °C ambient, TJ ≈ 170 °C-exceeding the 150 °C max. Derating to 16 W or adding thermal vias/heatsink is required to maintain safe operation.