Here is a circuit to evaluate the MCP1640 chip. This boost regulator has an amazing low voltage operation of 0.65 Volts and can provide from 2 up to 5.5 volts supply and 350mA of current! In other words, you can use two new or used AA batteries and drain their power down to almost zero! Think about this: If you connect the 2xAA in series, then the chip will still operate until they fall bellow 0.33V each one! And if you consider this wild, Microchip states that after start-up, the chip can operate at a minimum 0.35V, so our batteries will operate until they fall bellow 0.18V! Amazing, right?
Like all good things, this chip comes in a very small and in an ultra very small package, namely a 6-leaded SOT23 and a 2x3mm DFN package with the solder leads underneath (soldering iron cannot solder this part). It is perfect to be used in portable products such as LED flash lights due to its minimal size and minimum external parts. Typically, two capacitors, two resistors and a small inductor are needed. Nevertheless, it can be a nightmare for those who do not have experience with SMD packages due to the truly small size.
The circuit is extremely simple - You only need to follow the guidelines from the datasheed:
(Click to enlarge)
First, let's see the terminals that I've used. A 3-way terminal is used for the input (left side). This terminal has the Vin, the GND and the Enable signal. The batteries are connected at the Vin (+) and the GND (-) terminal. The Enable signal is used to enable the chip or not. Leaving the enable unconnected will shut down the chip. The chip that I've used (MCP1640 and MCP1640B) has a true-disconnect function when shut-off, during which the output is isolated by the input with a P-channel mosfet and draws as little as 1uA quiescence current. So you can safely use this as an on-off switch.
In case that you don't want to use the Enable input, I've added an extra jumper (like the ones used on the old HDDs to select master-slave). This jumper is the EN_BYPASS on the top left side. If this jumper is bridged, then the chip will be always operating. You can safely remove this jumper at will.
On the right side there is only one terminal. This is the output voltage, the positive (Vout) and the negative (GND)
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