This part is a kind of semiconductor called BL8521.

Function of this product has 3A Synchronous Buck Converter.

Manufacturers : SHANGHAI BELLING

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BL8521 5.5V, 1.4MHz, 3A Synchronous Buck Converter DESCRIPTION The BL8521 is a synchronous, 1.4MHz, fix frequency PWM Buck converter. It is ideal for powering portable equipment that powered by a single cell Lithium-ion batter, or USB port. The BL8521 can provide up to 3A of load current with output voltage as low as 0.8V. It can operate at 100% duty cycle for low dropout application. With its peak current mode control and outside compensation, the BL8521 is stable with ceramic capacitors and small inductors. BL8521 comprises a cycle-by-cycle current limit and thermal shutdown to protect itself from fault application. BL8521 is available in DFN 3x3 -10 package. FEATURES  Adjustable Output Voltage, 0.8 - Vin  High efficiency, up to 96%  Output voltage accuracy 2%  0.1ohm Rdso [ ... ]

BL8521 PDF Datasheet Download