Introduction
ASK831BSA is a non-isolated, highly integrated, low-cost PWM power switch designed for buck and buck-boost circuits. The device is fabricated using a high-voltage single-chip process, integrating a 500V high-voltage MOSFET and a controller employing peak current mode control on the same die. High-accuracy 5V default output is guaranteed across the full input voltage range. The minimum off-time is internally fixed at 32μs with frequency dithering, optimizing EMI performance while ensuring output power. The device incorporates light/heavy load modes, enabling standby power consumption below 50mW with ease. Comprehensive protection features are integrated, including VDD undervoltage lockout, cycle-by-cycle current limiting, abnormal overcurrent protection, overtemperature protection, overload protection, and short-circuit protection. Fabricated with high-voltage integrated process technology, it is suitable for offline buck and buck-boost circuits used in small home appliances and auxiliary power supply applications, and can also replace linear power supplies. The device is internally optimized for compatibility with ultra-low voltage input applications. The typical quiescent operating current is 150μA, reducing the required VDD capacitance. The system switching frequency depends on the load condition and the relationship between VDD voltage and the output voltage reference, resulting in frequency modulation (FM) operation. The internal differential sampling circuit senses the voltage drop across the high-voltage MOSFET current as the input to the internal overcurrent comparator. A leading-edge blanking circuit with a typical value of 400ns is implemented to prevent noise interference during turn-on transients. Under light load conditions, the system operates in discontinuous conduction mode and automatically reduces the peak current reference to meet ultra-low standby requirements. A soft-start function with a typical period of 4ms is integrated on-chip. When an overcurrent or short-circuit condition occurs, if the high-voltage MOSFET is triggered every oscillation cycle within a typical duration of 128ms, the device identifies this as a fault, halts switching, and then enters auto-restart mode. To prevent excessive inductor peak current, an internal abnormal overcurrent detection module is implemented with a typical threshold of 250mA. When the CS voltage exceeds this threshold, the internal power MOSFET turns off immediately and remains off for 2 cycles. The integrated overtemperature protection circuit monitors the die junction temperature; when it exceeds the typical value of 155°C, the system enters auto-restart mode. During auto-restart and VDD oscillation modes, the high-voltage MOSFET is not allowed to conduct, and the VDD capacitor voltage continuously oscillates between 4.87V and 4.38V. When the oscillation cycle count exceeds 511, the device exits protection mode and resumes normal operation. The soft-drive function is designed to optimize system EMI performance. To ensure stable system operation, it is recommended that the system operate in a shallow continuous conduction mode, where the inductor current ripple ΔI approaches the overcurrent protection peak current. The inductance calculation formula is as follows: L = (Vo + Vf) × Toff_min / ΔI, where Vo is the output voltage, Vf is the freewheeling diode forward voltage drop, and Toff_min is the internally set minimum off-time of the device, approximately 32μs.
