STMicroelectronics VIPER25LDTR

Overview

VIPER25LDTR from STMicroelectronics is an off-line quasi-resonant (QR) flyback controller IC with integrated 800 V avalanche-rugged N-channel power MOSFET, 7 Ω R_DS(on) at 25 °C, adjustable current limiting via ZCD pin, and <50 mW standby power at 265 V_AC. It targets compact AC/DC adapters for portable electronics and auxiliary supplies in TVs, LED drivers, and set-top boxes.

For engineers reviewing the VIPER25LDTR datasheet, VIPER25LDTR pinout, VIPER25LDTR application, or VIPER25LDTR equivalent, key selection criteria include its QR valley-switching control, dual overcurrent protection (0.7 A primary limit + 1.2 A second threshold), brown-in/brown-out hysteresis (50 mV), thermal shutdown at 155 °C, and SO-16N package with drain-connected heat-dissipating pins.

Technical Context

The VIPER25LDTR implements a current-mode PWM controller with zero-current detection (ZCD) for transformer demagnetization sensing, enabling valley-switching operation across line/load variations. Its internal oscillator supports frequency foldback and valley-skipping modes, with F_OSClim fixed at 136 kHz (L-type) to minimize EMI filter cost.

It integrates high-voltage startup (60–100 V DRAIN start threshold), on-board soft-start (3.5 ms), burst-mode operation below 0.6 V FB, and four-level protection: cycle-by-cycle OCP, second OCP, overvoltage (4.2 V threshold), and hysteretic thermal shutdown (155 °C / 30 °C hysteresis).

Key Specifications

Pinout & Package

Package: SO-16N (16-pin small outline, exposed drain pad for thermal dissipation). Pins 13–16 are internally connected to the metal frame and serve as high-current drain terminals with enhanced thermal conduction.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quasi-resonant flyback controller applications.

Compared with ICE2QS03G and VIPER06XS, VIPER25LDTR uniquely combines 800 V integration, ZCD-based QR control, and adjustable current limiting in one SO-16N package-making it optimal for space-constrained 10–20 W adapters requiring minimal external components and ultra-low standby power.

Availability

VIPER25LDTR is available at Aetrix Electronics and suitable for USB-C adapters, LED driver auxiliary supplies, LCD TV standby rails, and set-top box SMPS requiring stable component supply and long-term industrial availability.

Supply support for VIPER25LDTR 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, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

VIPER25LDTR belongs to ST's VIPer™ high-voltage AC-DC converter family, engineered specifically for compact, low-component-count offline SMPS in cost-sensitive and space-constrained applications.

FAQ

What is the purpose of the ZCD pin in VIPER25LDTR?

The ZCD pin serves three critical functions: (1) zero-current detection for quasi-resonant valley switching, (2) adjustable primary current limit set point via external resistor RLIM, and (3) overvoltage protection input with digital strobing and noise immunity. It directly interfaces with the auxiliary winding to sense transformer demagnetization timing and enables feed-forward compensation for line-voltage variation.

How does VIPER25LDTR achieve <50 mW standby power?

VIPER25LDTR achieves sub-50 mW standby power through burst-mode operation (activated when FB voltage falls below 0.6 V), ultra-low quiescent current in shutdown (<400 µA), and automatic disabling of the high-voltage startup circuit once VDD reaches operating voltage. The internal oscillator halts during burst intervals, and the power MOSFET remains off for extended periods-minimizing all switching and conduction losses.

Can VIPER25LDTR operate without an auxiliary winding?

No-VIPER25LDTR requires an auxiliary winding to sustain VDD after startup. The internal HV startup circuit only charges the VDD capacitor initially; once VDD exceeds 14 V, the HV generator disables and the IC relies entirely on energy from the auxiliary winding via a steering diode. Without this winding, VDD collapses below 8.5 V, triggering UVLO and halting operation.

What thermal design considerations apply to the SO-16N package?

The SO-16N package uses pins 13–16 as thermal pads connected to the MOSFET drain. To meet the 1.5 W power dissipation limit at T_A < 60 °C, ≥100 mm² of 35 µm copper must be placed beneath these pins on the PCB. With this layout, junction-to-ambient thermal resistance drops to 85 °C/W-enabling reliable 12 W continuous operation in open-frame designs without forced air.