Buck Boost Voltage Converter

Posted on Feb 4, 2014

Sometimes it is desired to power a circuit from a battery where the required supply voltage lies within the discharge curve of the battery. If the battery is new, the circuit receives a higher voltage than required, whereas if the battery is towards the end of its life, the voltage will not be high enough. This is where the new LTC 3440 buck/boost

 Buck Boost Voltage Converter
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voltage converter from Linear Technology ( can help. The switching regulator in Figure 1 converts an input voltage in the range +2. 7 V to +4. 5 V into an output voltage in the range +2. 5 V to +5. 5 V using one tiny coil. The level of the output voltage is set by the voltage divider formed by R2 and R3. The device switches as necessary between step-up (or boost`) operation when Vin is less than Vout, and step-down (or buck`) operation when Vin is greater than Vout. The maximum available output current is 600mA. The IC contains four MOSFET switches (Figure 2) which can connect the input side of coil L1 either to Vin or to ground, and the output side of L1 either to the output voltage or to ground. In step-up operation switch A is permanently on and switch B permanently off. Switches C and D close alternately, storing energy from the input in the inductor and then releasing it into the output to create an output voltage higher than the input voltage. In step-down operation switch D is permanently closed and switch C permanently open. Switches A and B close alternately and so create a lower voltage at Vout in proportion to the mark-space ratio of the switch ing signal. L1, together with the output capacitor, form a low-pass filter. If the input and output voltages are approximately the same, the IC switches into a pulse-width modulation mode using all four switches. Resistor R1 sets the switching frequency of the IC, which...

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