L4985A [STMicroelectronics]

The L4985 is a peak current-mode PFC controller for boost converter with a proprietary multiplier “emulator” which in addition to the innovative THD optimizers guarantee very low Total Harmonic Distortion (THD) performance in all operating conditions. The device comes in a pin SO package and offers a high performance/low-component count solution for CCM-operated boost PFC pre-regulators in EN61000-3-2 and JEIDA-MITI compliant applications, in a power range that spans from few hundred W to some kW.

The device, thanks to a proprietary off-time modulator, operates in quasi-fixed frequency in all operating conditions. Two options are available, 65 kHz for A and 130 kHz for B.

The 800V high voltage start-up block includes also the circuitry to discharge the X-capacitors of the EMI filter to a safe level. This allows the unit to meet safety regulation (such as IEC 61010-1 or IEC 62368-1) without using the traditional discharge resistor in parallel to the X-capacitors.

The device features low consumption and disable functions allowing usage in applications supposed to comply even with the latest energy saving requirements issued by Energy Star, the Department of Energy (DoE) in the United States, the European Code of Conduct, the European Union’s Ecodesign Directive, and other guidelines.

In addition to an overvoltage protection able to keep the output voltage under control during transient conditions, the IC is provided also with a protection against feedback loop failures or erroneous settings and boost inductor saturation. The brownout protection function allows to design medical equipment according to the latest regulations driven by IEC 60601-1-2 which requires the output regulation in case of mains dips lasting up to 500 msec. Soft-start limits the peak current.

The totem-pole output stage, capable of 0.7 A source and 1.5 A sink current, is suitable for big MOSFET or IGBT drives.

• Peak current mode CCM-operated
• 800 V high voltage startup with integrated input voltage sensing
• Active input filter capacitor discharge
• Proprietary multiplier “emulator” with minimum THD of line current in all operating conditions (CCM and DCM)
• Extremely few external components
• Protections: feedback loop failure, OVP, OCP, inductor saturation, brown-in, brownout (compliant to medical SMPS standards)
• Inductor current sense
• Disable and low consumption function
• In-rush current monitoring
• Soft-start for smooth startup
• 1.2% (@ Tj = 25 °C) internal reference voltage
• 65 kHz (A version) and 130 kHz (B version) switching frequency
• SO8 package