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  • MCP16251 One-Cell Boost Converter

  • Created: Mar 20, 2017

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Oftentimes, batteries are convenient choice to be used in some designs that require DC supply. The only problem is that there are certain applications wherein battery’s available voltage is not suitable for the system being supplied. Another problem with batteries is that their output voltage varies as the available charge is used up, and at some point the battery voltage becomes too low to power the circuit. The solution to this problem is to use fewer batteries and to boost the available DC voltage to the required level by using a boost converter. Also, by using a boost converter, low output level can be boosted back to extend battery life.

This reference design is a MCP16251 one-cell boost converter with external undervoltage lockout circuit. The MCP16251 is a high-efficiency, fixed-frequency, synchronous step-up DC-DC converter. The device provides a true output disconnect feature while in shutdown (EN=GND). The board can be powered from an AA alkaline battery, which typically has 2500mAh capacity at low currents. If jumper J1is connected and switch SW1 is turned off, the application will start in Sleep mode. While in this state, the EN voltage is 0V (because it is being pulled down by resistor R4) and the boost converter is disabled. Turning SW1 ON, the UVLO circuit is active and starts monitoring the VIN voltage. If the battery voltage is higher than 1.1V, transistor Q1 turns on, injecting current in the base of transistor Q2, which also turns on and biases resistor R3. This causes the voltage at the EN pin to go high. Because resistor R4 acts as a load for transistor Q1, the collector current of Q1 is small, meaning its collector-emitter saturation voltage (VCE) can be neglected; thus, VEN is equal to VIN and the MCP16251 turns ON. As transistor Q2 bypasses resistor R3, its base-emitter voltage (VBE) begins to increase, keeping transistor Q1 ON as long as VIN > 0.8V. Transistor Q2 and resistor R3 form the hysteresis block.

The design is developed to provide a solution for applications that require fixed start-up/shutdown thresholds. The board features a discrete UVLO circuit implemented with bipolar junction transistors. The very low quiescent current makes it ideal for battery-powered applications. The MCP16251 device is developed to optimize battery life by having a very low quiescent current, typically 4uA, and a small, no load input current, typically 14uA. The MCP16251 is capable of regulating the output voltage over a wide range (1.8V to 5.5V) and typically delivers over a 100mA load current at a 3.3V output when supplied from a single 1.5V cell.



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