POWER INTEGRATIONS LNK6425D

The LinkSwitch-3 family of ICs dramatically simplifies low power CV/ CC charger designs by eliminating an optocoupler and secondary control circuitry. The device introduces a revolutionary control technique to provide very accurate output voltage and current regulation, compensating for transformer and internal parameter tolerances along with input voltage variations. The device incorporates a 725 V power MOSFET, a novel ON/OFF control state machine, a high-voltage switched current source for self biasing, frequency jittering, cycle-by-cycle current limit and hysteretic thermal shutdown circuitry onto a monolithic IC. The LinkSwitch-3 combines a high-voltage power MOSFET switch with a power supply controller in one device. It uses an ON/OFF control to regulate the output voltage. In addition, the switching frequency is modulated to regulate the output current to provide a constant current characteristic. The LinkSwitch-3 controller consists of an oscillator, feedback (sense and logic) circuit, 6 V regulator, over-temperature protection, frequency jittering, current limit circuit, leading-edge blanking, inductance correction circuitry, frequency control for constant current regulation and ON/OFF state machine for CV control. If the primary magnetizing inductance is either too high or low the converter will automatically compensate for this by adjusting the oscillator frequency. Since this controller is designed to operate in discontinuous-conduction mode the output power is directly proportional to the set primary inductance and its tolerance can be completely compensated with adjustments to the switching frequency. As the output voltage and therefore the flyback voltage across the bias winding ramps up, the FEEDBACK pin voltage increases. The switching frequency is adjusted as the FEEDBACK pin voltage increases to provide a constant output current regulation. The constant current circuit and the inductance correction circuit are designed to operate concurrently in the CC region. As the FEEDBACK pin approaches 2 V from the constant current regulation mode, the power supply transitions into CV operation. The switching frequency at this point is at its maximum value, corresponding to the peak power point of the CV/CC characteristic. The controller regulates the FEEDBACK pin voltage to remain at FEEDBACK pin threshold (VFBTH) using an ON/OFF state-machine.

• Eliminates optocoupler and all secondary CV/CC control circuitry
• Eliminates all control loop compensation circuitry
• Compensates for transformer inductance tolerances
• Compensates for input line voltage variations
• Compensates for cable voltage drop
• Compensates for external component temperature variations
• Very accurate IC parameter tolerances using test trimming technology
• Frequency jittering greatly reduces EMI filter cost
• Programmable switching frequency up to 85 kHz to reduce transformer size
• Minimum operation frequency fixed to improve transient load response
• Auto-restart protection reduces power delivered by >90% for output short-circuit and control loop faults (open and shorted components)
• Hysteretic thermal shutdown – automatic recovery reduces power supply returns from the field
• Meets high-voltage creepage requirements between DRAIN and all other pins both on the PCB and at the package
• Easily meets all global energy efficiency regulations with no added components
• No-load consumption at 230 VAC input with bias winding <10 mW for LNK64x4-LNK64x6 and <30 mW for LNK64x7-LNK64x8
• ON/OFF control provides constant efficiency down to very light loads – ideal for CEC regulations
• No current sense resistors – maximizes efficiency
• Halogen free and RoHS compliant package

• Chargers for cell/cordless phones, PDAs, MP3/portable audio devices, adapters, etc.