Hi, I think this is a question for Paul. I have a Teensy 3.0 and I want to protect the RTC from power loss by connecting our LiON battery to the Vbat pin. And that is what I have done on my first prototype. But before I build up more boards I'm wondering if what I did is "safe" and couldn't harm the Teensy processor.
My thinking is that section 4.4 of the Freescale MCU data sheet says that the max operating value allowed for Vbat is 3.8V. Based on how they define limits in the data sheet it implies that if you go over 3.8V you could break the chip. And my (fairly standard) LiON battery can put of 4.2V max or so. I see that there is a dual diode between the Vbat external pin and the MCU Vbat pin. But I saw a post where Paul said that diode was a PMEG4010CPA Schottky diode. And checking the data sheet for it, the forward voltage drop across it is below .4V and, for low current, much below .4V. So I would think I could be driving the MCU Vbat pin with too high a voltage. But my board isn't dead yet and I've been doing this for months.
I'm wondering if anyone has any thoughts on whether this is safe or if I should add some external part between the battery and the Teensy VBat pin?
My thinking is that section 4.4 of the Freescale MCU data sheet says that the max operating value allowed for Vbat is 3.8V. Based on how they define limits in the data sheet it implies that if you go over 3.8V you could break the chip. And my (fairly standard) LiON battery can put of 4.2V max or so. I see that there is a dual diode between the Vbat external pin and the MCU Vbat pin. But I saw a post where Paul said that diode was a PMEG4010CPA Schottky diode. And checking the data sheet for it, the forward voltage drop across it is below .4V and, for low current, much below .4V. So I would think I could be driving the MCU Vbat pin with too high a voltage. But my board isn't dead yet and I've been doing this for months.
I'm wondering if anyone has any thoughts on whether this is safe or if I should add some external part between the battery and the Teensy VBat pin?