Step-Down Converter Controller

  
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The TPS6420x controller is designed to operate from one to three series-connected cells or from a 3. 3 V or 5 V supply obtained from a USB port. At its output it can produce 3. 3 V at 2 A, suitable for powering a microcontroller-based system. With a suitable choice of external components (inductor, P-channel MOSFET and Schottky diode) the device can
Step-Down Converter Controller - schematic

be operated over a wide range of possible output voltages and currents. A further advantage is its extremely low quiescent current consumption in power-down mode (100 nA typical) and in no-load operation (20 mA). Also, if the input voltage is less than or equal to the desired output voltage, the device can connect the output directly to the input. Using just a few external components the TPS6420x can cover an output voltage range from 1. 2 V up to the input voltage at up to 3 A, as long as a suitable P-channel MOSFET and Schottky diode are used. The device is an asynchronous step-down converter which, unlike the more widely-used PFM (pulse-frequency modulation) and PWM (pulse width modulation) types, involves a constant on-time and/or constant off-time. Conventional controllers operate in PWM mode at medium to high loads, switching to PFM at lower loads in order to minimise switching losses. The controller described here also adjusts its switching frequency in accordance with the load to achieve a similar effect to the PFM/PWM controllers. The circuit diagram shows a classical step-down converter with an input voltage range from 3. 3 V to 6 V and an output voltage of 3. 3 V at a current of up to 2 A. The optional 33 m shunt resistor provides for current limiting. The TPS64202 offers a minimum on-time selectable between 1. 6 ms, 0. 8 ms, 0. 4 ms and 0. 2 ms and a fixed off-time of 300 ns. A MOSFET in the supply voltage path...



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