I am using a boost converter (MCP1640) to convert a regulated 3.3V up to a higher voltage (5V in my current testing, but 4V ultimately). I am seeing a current draw of 150mA-350mA (depending on conditions) *before* adding any load. Going from the datasheet, unless I am mistaken, this should be under 1mA.
Link for the MCP1640:
http://www.microchip.com/wwwproducts/en/en547080I am wondering why the current draw is so high. I am not particularly familiar with boost converters and inductors, so I don't have a lot of experience to draw on here.
If I add a small load (eg. a single LED), the current increases roughly as expected. The amount is generally a sensible ratio of the current you'd expect to flow through a LED given the voltage difference, eg. maybe 10mA or so depending on specifics.
This is a MCP1640B (note: "B"), which has an enable pin that when driven low should pass the input straight to the output. Even when I do this, the current remains around 150mA.
I don't have the recommended capacitors from the datasheet. I realise that this may be the cause of the problem. The datasheet recommends a 4.7uF ceramic for the input and 10uF ceramic cap for the output. Unfortunately I don't have any ceramic caps above 1uF on hand (plenty of electrolytics though). I've experimented with combinations of the ceramics and electrolytics that I have instead. The results are fairly consistent.
I have swapped the chip out with another (same batch), and it appears to behave the same way.
I've dropped the part of the circuit that fed into the converter and used an AA battery as input. I see similar results.
I've heard of problems with the MCP1640 before when connected with long wires. Whilst a breadboard-based design, I've still managed to pack all of the components into a 20mmx15mm area. The chip itself is on a small breakout board.
I have experimented with different inductors. When using a 4.7uH Murata 1100R, I generally saw around 300mA current draw. A 4.7uH Wurth WE-ZB caused about 180mA. A 10uH "ebay special" (bought cheap off of ebay, I don't know exactly what it is) used anywhere from 100mA-300mA. I lit a single LED with each, and the first two inductors did so reliably. Note that these inductors are *not* in the recommended list in the datasheet, they're just what I had available.
The generated voltage was close with each inductor. I used resistors that should generate 4.8V (330k bottom, 1M top), and saw voltages of 4.95V-4.99V being produced. So the voltage is roughly right.
I've checked the wiring repeatedly and cannot find a fault. The setup fairly closely follows the example given on page two of the datasheet, but uses 330k and 1M resistors instead on the feedback pin.
I'll probably be able to determine more once I have the recommended parts, but that may be some time away.
I am wondering if anyone familiar with boost converters and inductors is able to offer insight into what may be happening? Is this sort of current draw normal? Are there any critical elements to working with boost converters that I am not aware of? How suitable are the inductors I ended up trying? And so forth.