DC MOTOR LOW BATTERY LED PROBLEM

[amintegia]

Hello everyone,

I have designed a circuit which is powered by a 3.7V LIPO battery. This supply voltage passes through a LDO (IC1 in the schematic) which regulates the voltage to 3V to feed a small DC motor (+3V_MOTOR).

In addition, it integrates a low battery detection circuit based on the TL431 (IC2), which activates a low battery LED (D1-LOW_BATT signal) when the battery voltage reaches 3V.

For activation of the DC motor, a button has to be pressed which causes the battery voltage to reach the LDO (BAT+_PULS signal) and then the motor. Therefore, only when this button is pressed, the battery voltage is measured and the LED is activated if necessary.

The general operation of the motor activation is correct. However, in the voltage range where the low battery LED should not activate I see a small flashing of the LED mainly when pressing and releasing.

I have thought that this effect could be due to the flyback effect during the shutdown of our dc motor. But as I mentioned before, this effect also occurs on activation.

Another idea that has occurred to me is that the battery has peak drops when this current is required to power the motor and that is when the low battery circuit detects these drops and activates the red LED for a few ms.

I'm attaching the schematic of the PCB.

[amintegia]

Could anyone give any clue about the issue?

I will really appreciate it.

[Kean]

The low battery voltage detection seems to be connected to the battery only when the button is pressed.
So I guess it will flash the LED every time it is connected and disconnected from the battery.