STMicroelectronics VIPER22AS

Overview

VIPER22AS from STMicroelectronics is a monolithic high-voltage off-line SMPS primary switcher integrating a current-mode PWM controller and 730 V avalanche-rated Power MOSFET in SO-8 package. It delivers up to 12 W (European mains) or 7 W (universal input), operates at fixed 60 kHz, supports 9–38 V VDD range, and features automatic burst mode, overvoltage hiccup protection, and thermal shutdown - used in battery charger adapters and TV standby supplies.

For engineers reviewing the VIPER22AS datasheet, VIPER22AS pinout, VIPER22AS application, or VIPER22AS equivalent, key selection criteria include its integrated HV start-up current source, FB pin current-sensing architecture, VDD hysteresis (6.5 V typ), and SO-8 thermal resistance (25 °C/W junction-to-pins).

Technical Context

The VIPER22AS implements current-mode control via an internal transconductance amplifier comparing FB pin current against a 0.23 V reference across R2. Its oscillator is temperature-compensated (±6% over 0–100 °C), and blanking time (500 ns) prevents false triggering during switching transitions.

Start-up relies on a high-voltage current source connected to DRAIN, charging the external VDD capacitor until VDD reaches 14.5 V (VDDon); shutdown occurs at 8 V (VDDoff). Overvoltage protection triggers at 42 V (VDDovp) and resets automatically after VDD falls below VDDoff.

Key Specifications

Pinout & Package

SO-8 surface-mount package with exposed DRAIN pins for enhanced thermal dissipation (R_thj-case = 25 °C/W). All DRAIN pins internally connected; SOURCE serves as power ground reference.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar primary-side SMPS controller applications.

Compared with ICE2A265 and LNK304P, the VIPER22AS uniquely combines 730 V rating, integrated HV start-up, and 9–38 V VDD hysteresis - making it optimal for cost-sensitive, universal-input battery chargers where auxiliary winding stability varies widely.

Availability

VIPER22AS is available at Aetrix Electronics and suitable for battery charger adapters, TV standby supplies, and auxiliary motor control supplies requiring stable component supply and long-term industrial availability.

Supply support for VIPER22AS 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, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

The VIPER™ family targets highly integrated, low-cost off-line SMPS controllers - optimized for universal-input, low-to-medium power applications where integration, reliability, and thermal robustness are critical.

FAQ

What is the minimum recommended VDD capacitor value for reliable start-up?

A 100 nF ceramic capacitor is sufficient when using forward-converter auxiliary winding supply, as specified in Figure 8. Lower values risk premature start-up termination before auxiliary energy transfer begins. For designs with slow-rising auxiliary voltage, 470 nF is recommended to ensure t_ss exceeds worst-case energy transfer delay.

How does the FB pin current-sensing mechanism affect secondary-side regulation accuracy?

The FB pin draws current proportional to secondary-side error signal via optocoupler CTR. Regulation accuracy depends on CTR tolerance, LED forward voltage drift, and FB pin input impedance (1.2 kΩ). With TSM101-based dual-loop feedback, typical output voltage regulation is ±3% and current regulation ±5% over line/load/temperature.

Can VIPER22AS operate without an auxiliary winding?

No - the internal VDD supply relies on energy transferred from an auxiliary winding. The HV start-up current source only charges the VDD capacitor initially; sustained operation requires continuous auxiliary winding power. Designs omitting auxiliary windings must use external bias supplies tied to VDD.

What is the impact of R_DS(on) increase at elevated temperature on thermal design?

R_DS(on) rises to 31 Ω at 100 °C (max), increasing conduction loss by ~80% versus room-temperature value. This demands careful PCB copper area allocation (200 mm² minimum) and derating of peak power capability above 85 °C ambient to avoid thermal runaway.