A couple of quick questions about disabling the SparkFun Buck-Boost Converter.
First, the Buck-Boost draws about 60 uA when enabled (EN = HIGH). However, when disabled (EN = LOW), the current jumps to 0.5 mA. The TPS63070 has a very low shutdown current (~2 uA), so I’m wondering how/why the current draw is increasing when disabled.
Second, I’ve noticed that it takes a long time (>60 s) to actually shut down the regulator using the EN pin driven by an Arduino GPIO pin. Is this just typical behaviour of the Buck-Boost Converter?
Buck-Boost draws about 60 uA when enabled (EN = HIGH). However, when disabled (EN = LOW), the current jumps to 0.5 mA. The TPS63070 has a very low shutdown current (~2 uA), so I’m wondering how/why the current draw is increasing when disabled.
I think what you're seeing is current through the pullup resistor that holds EN high. When you pull it low, you connect VIN to ground through a 10K resistor. With a 5 volt input that should give you about a half a mA drain on the input. A 100K or 1M resistor would probably also work and would reduce the off state current by a factor of 10 or 100.
Second, I’ve noticed that it takes a long time (>60 s) to actually shut down the regulator using the EN pin driven by an Arduino GPIO pin. Is this just typical behaviour of the Buck-Boost Converter?
There's quite a bit of capacitance on the output that acts as a filter. I think what you're seeing is those capacitors bleeding off charge. If you put a load resistor (say 1-5K) on the output, those should bleed off quicker and the voltage should fall to zero faster.
TS-Chris:
I think what you’re seeing is current through the pullup resistor that holds EN high. When you pull it low, you connect VIN to ground through a 10K resistor. With a 5 volt input that should give you about a half a mA drain on the input. A 100K or 1M resistor would probably also work and would reduce the off state current by a factor of 10 or 100.
This makes sense! It also sounds like you’re right about the 1 MΩ resistor being better suited for the design. This would have effectively reduced the disabled current draw from 0.5 mA to 5 uA.
It looks like this is also suggested in the TPS63070 datasheet:
It is recommended to not connect EN directly to VIN but use a resistor in series in the range of 1kΩ to 1MΩ. If several inputs like EN and PS/SYNC are connected to VIN, the resistor can be shared.
