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Transition from battery to 5V on i.mx28

Question asked by Asmus Hansen on Feb 10, 2016
Latest reply on Feb 11, 2016 by Yuri Muhin



I'm making a kernel module for my i.mx28 application which is responsible for detecting 5V insertion and then make the system use the 5V supply instead of the battery as the power source for my embedded system.


In the application note An4199 rev. 0, it says that i'm supposed to enable the 4P2 LinReg and switch the DCDC converter to use the 4P2 Linreg(section 4.2.1).


I follow the steps for enabling the 4P2 LinReg as stated in section, then i charge the capacitor as stated in section and finally i enable the 4P2 input for DC-DC by following the steps in section where i also adjust the LinReg offset's to avoid contention, as mentioned in section


When i insert the 5V supply after removal, my ISR starts executing the above steps. Meanwhile i have an oscciloscope to measure the output of the 4P2 regulator from a testpin. I notice that when i start the embedded system with 5V as the power source and battery as backup, the voltage of the 4P2 pin is 4.2V. When i remove the 5V source, the 4P2 pin drops to 3.8V(Battery voltage) and finally when i insert the 5V supply again, the voltage on the 4P2 pin drops to 3.14V.


As a result of this, i suspect that the internal DC-DC converter continues to use the battery as a power source, since the power draw from the battery is approx 300mA. I think my problem is that the 4P2 regulator never starts to function properly, but i cannot figure out why.

As mentioned above, i have followed the steps for enabling the regulator and double checked the register values.


I hope some of you may be able to help.