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I've bought new S7v8A step-up/step-down voltage regulator which should give me on output 2.7-8V. However, when using multimeter I am adjusting correct value let say to around 5V (it really doesn't matter it happens all the time) and then connect it to my board (Teensy 3.1) it immediately drops the voltage to 0.84V.

What can cause this error and is there a way to fix it?

EDIT1: According to documentation the microcontroller max current value is 185 mA. I didn't find any information about minimum load. The regulator has 4 pins connected as shown below:

schematic

simulate this circuit – Schematic created using CircuitLab

According to the info from the website:

The SHDN pin can be driven low (under 0.4 V) to power down the regulator and put it in a low-power state. The quiescent current in this sleep mode is dominated by the current in the 100k pull-up resistor from SHDN to VIN. With SHDN held low, this resistor will draw 10 µA per volt on VIN (for example, the sleep current with a 5 V input will be 50 µA). The SHDN pin can be driven high (above 1.2 V) to enable the board, or it can be connected to VIN or left disconnected if you want to leave the board permanently enabled.

The SHDN pin can be left not connected and it should still work correctly.

So as you can see it is quite strange behavior (at least I guess so).

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  • \$\begingroup\$ What current does your board consume? Is it within the spec of the regulator? \$\endgroup\$ – anrieff Nov 21 '14 at 15:54
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    \$\begingroup\$ I assume you mean S7V8A. Spelling matters. Does the regulator have a minimum load requirement, and are you using it when you're adjusting the voltage? \$\endgroup\$ – Dave Tweed Nov 21 '14 at 16:02
  • \$\begingroup\$ @DaveTweed Yes, you are right, my mistake. I've corrected it and add edit to my question. \$\endgroup\$ – sebap123 Nov 21 '14 at 16:32
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I found what was wrong with my circuit. It was low battery current, because it was around 2mA and it was way to little to power anything. Now when I switched to newer battery everything works great.

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