STMicroelectronics VIPER122LSTR

Overview

VIPER122LSTR from STMicroelectronics is a 730 V high-voltage offline PWM converter IC integrating a rugged power MOSFET, current-mode controller, 3.3 V reference, frequency jittering, and burst-mode operation. It delivers up to 11 W in open-frame designs at 50 °C ambient, supports flyback/buck topologies, and achieves ≤40 mW no-load input power at 230 VAC for auxiliary SMPS in home appliances and lighting.

For engineers reviewing the VIPER122LSTR datasheet, VIPER122LSTR pinout, VIPER122LSTR application, or VIPER122LSTR equivalent, key selection criteria include its integrated 730 V MOSFET, 60 kHz switching frequency with ±4 kHz modulation depth, thermal shutdown at 150 °C, short-circuit protection with 50 ms trip delay, and SSOP10 package compatibility with PCB copper-area heat sinking.

Technical Context

The VIPER122LSTR implements a current-mode PWM control architecture with internal high-voltage startup (45 V drain start threshold), cycle-by-cycle primary current sensing, and dual-loop regulation via EA-IN/E-A-OUT pins. Its error amplifier features 2 mA/V transconductance and 15 kΩ dynamic input resistance, enabling stable compensation with external RC networks.

Burst mode activation occurs when EA-OUT falls below 1.1 V (typ.), clamping peak drain current to ~85 mA to suppress audible noise; thermal shutdown triggers at 150 °C with 30 °C hysteresis, and VCC clamp protection activates when both ILIM (0.45 A) and ICC_FAIL (4 mA) thresholds are exceeded simultaneously.

Key Specifications

Pinout & Package

The VIPER122LSTR is housed in a 10-pin SSOP (Shrink Small Outline Package) with exposed thermal pad, optimized for surface-mount assembly and PCB copper-area heat dissipation. Pin 6–10 share the DRAIN terminal, requiring direct connection to transformer primary and large copper pour for thermal management.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage offline converter applications.

Compared with ICE2QS03G and LNK306P, the VIPER122LSTR provides superior EMI performance via jittering, lower standby consumption, and tighter thermal protection-making it optimal for compact, low-noise auxiliary SMPS where board space and acoustic noise are critical.

Availability

VIPER122LSTR is available at Aetrix Electronics and suitable for smart home power supplies, LED driver auxiliary rails, industrial control panel PSUs, and appliance mainboard aux supplies requiring stable component supply across extended production lifecycles.

Supply support for VIPER122LSTR 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, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets since 1987.

The VIPER™ family targets cost-sensitive, high-reliability offline power conversion-specifically engineered to replace discrete HV FET + controller combinations in auxiliary SMPS for appliances, lighting, and industrial controls.

FAQ

What is the minimum recommended copper area for thermal management of VIPER122LSTR in SSOP10?

The datasheet specifies that mounting on a standard FR4 board with 100 mm² (0.155 in²) of 35 μm-thick copper reduces junction-to-ambient thermal resistance from 155 °C/W to 95 °C/W. For continuous 11 W operation at 50 °C ambient, ≥200 mm² copper pour connected to DRAIN pins is recommended to maintain TJ < 125 °C under worst-case convection conditions.

Can VIPER122LSTR operate in buck topology without an optocoupler?

Yes-VIPER122LSTR supports non-isolated buck operation using direct resistor-divider feedback to EA-IN. The device's internal current-mode control and 3.3 V reference enable stable regulation; typical designs use a 10 kΩ/2.2 kΩ divider for 12 V output, with compensation network on EA-OUT. No optocoupler or isolation is required in this configuration.

How does the burst mode threshold interact with the error amplifier output voltage?

Burst mode activates when EA-OUT falls below 1.1 V (typ.), with 40 mV hysteresis. Below this threshold, switching halts until EA-OUT rises above 1.14 V. During burst, peak drain current is clamped to ~85 mA to prevent transformer audible noise-this is independent of the main ILIM setting (0.45 A) and applies only during low-duty-cycle operation.

What happens during VCC clamp protection activation, and how is it cleared?

VCC clamp protection triggers when both ILIM (0.45 A) and ICC_FAIL (4 mA) conditions occur simultaneously-indicating feedback failure or overcurrent. The device stops switching for exactly 1 second, then automatically restarts. If the fault persists, the cycle repeats. No external reset or power cycle is needed, ensuring robust recovery in field-deployed systems.