L4985B

Overview

The STMicroelectronics L4985B is a continuous conduction mode (CCM) power factor correction controller designed for boost converters. It features an 800V high-voltage startup block and active X-capacitor discharge circuitry, enabling compliance with IEC 61010-1 and IEC 62368-1 safety standards without external resistors. The device utilizes a proprietary multiplier simulator and THD optimizer to ensure minimal total harmonic distortion across all operating conditions. It operates at a quasi-fixed frequency of 130 kHz, providing a low-component-count solution for AC/DC pre-regulators ranging from hundreds of watts to several kilowatts.

Feature Summary

• Proprietary multiplier simulator and THD optimizer for minimal line current distortion
• Integrated 800V high-voltage startup with active EMI filter capacitor discharge
• Quasi-fixed frequency operation via dedicated off-time modulator
• Comprehensive protection including OVP, OCP, inductor saturation, and feedback loop fault

Applications

• AC/DC adapters compliant with EN61000-3-2 Class-D and JEITA-MITI standards
• SMPS designs requiring medical safety compliance (IEC 60601-1-1)
• High-efficiency power supplies meeting Energy Star and EuP Lot 6 Tier 2 requirements
• Pre-regulators for industrial and telecom equipment

Procurement Notes

Verify the specific suffix 'B' corresponds to the 130 kHz switching frequency variant when sourcing. Confirm package integrity for SO-8 components. Ensure documentation matches the active status and revision history provided by STMicroelectronics. Cross-reference safety certifications required for your target market against the integrated discharge capabilities.

Selection Notes

Select the L4985B over the A version when higher switching frequencies are required to reduce passive component size. The integrated 800V startup simplifies design by eliminating traditional discharge resistors. Consider the peak current mode control for robust performance in CCM applications. Evaluate thermal management needs based on the 130 kHz operation and expected load ranges.

Part Context

The L4985 series represents STMicroelectronics' advanced CCM PFC controllers, succeeding earlier models like the L4981. It addresses modern efficiency mandates and safety regulations through integrated high-voltage features. The B variant specifically targets applications benefiting from reduced magnetic component sizes due to its 130 kHz operating frequency, offering a balance between performance and complexity.

Replacement Considerations

The L4985A serves as a direct functional substitute if a 65 kHz switching frequency is acceptable. Both variants share identical pinouts and core control logic, differing primarily in internal oscillator settings. Verify that the application's EMI filter design accommodates the frequency change when swapping between A and B versions.