I've been working on a project for a while now that requires it to be powered from a pack of 4 AAA batteries in series. The output from those batteries is connected to a TPS709 3.3V regulator. Per its datasheet recommendation, I installed a 2.2 µF tantalum bypass capacitor at its output. I didn't bother placing a cap at its input other than a standard 0.1 µF because the batteries powering it are at close proximity and are not subject to sudden demand surges.
Anyway, the circuit being powered by said batteries draws very little current (just as I want it to), with my instruments showing a 14.7 µA draw from the battery pack. But sometimes I have to connect what I call a "comm card" to said circuit, which consists of a MCP2221A USB to UART converter and a couple of LEDs. When said card is connected to the circuit, it draws its power from the TPS709 regulator. Well, I discovered that connecting the card caused the MCU installed in it to sometimes reset itself. And I attributed said phenomena to the sudden current demand from the TPS709 when it tried to start up the MCP2221A chip.
My solution was to change the 2.2 µF cap at the regulator's output and replace it with a 10 µF cap, also tantalum. Lo and behold! the spurious MCU resets that sometimes manifested themselves whenever I plugged the "comm card" to my circuit were no more!
Problem solved, or so I thought. After changing the tantalum cap, I re-checked how much current my circuit was drawing, and I now had a reading of 15.1 µA instead of 14.7 µA. I am blaming the 0.4µA difference in the new cap's intrinsic leakage current.
Question, am I using the best capacitor for this application? Is there a better type of cap other than tantalum out there with an even lower leakage current value?
Anyway, the circuit being powered by said batteries draws very little current (just as I want it to), with my instruments showing a 14.7 µA draw from the battery pack. But sometimes I have to connect what I call a "comm card" to said circuit, which consists of a MCP2221A USB to UART converter and a couple of LEDs. When said card is connected to the circuit, it draws its power from the TPS709 regulator. Well, I discovered that connecting the card caused the MCU installed in it to sometimes reset itself. And I attributed said phenomena to the sudden current demand from the TPS709 when it tried to start up the MCP2221A chip.
My solution was to change the 2.2 µF cap at the regulator's output and replace it with a 10 µF cap, also tantalum. Lo and behold! the spurious MCU resets that sometimes manifested themselves whenever I plugged the "comm card" to my circuit were no more!
Problem solved, or so I thought. After changing the tantalum cap, I re-checked how much current my circuit was drawing, and I now had a reading of 15.1 µA instead of 14.7 µA. I am blaming the 0.4µA difference in the new cap's intrinsic leakage current.
Question, am I using the best capacitor for this application? Is there a better type of cap other than tantalum out there with an even lower leakage current value?