Not only pull-up, also RTC is powered by 5V. Correct logic levels aren't guaranteed with mixed voltage design. I also notice that MCU supply can be switched off while 5V is maintained. Bad idea, asking for trouble.1. the I2C pull-up resistors connect to 5V but the MCU is powered from 3.3V so logic high may be excessive for the MCU, better to tie them to a 3.3V supply.
I applied these changes including changing pullup resistors to 3v3 and putting diodes for regulators. but nothing has changed and the problem is not solved. I guess there is a filter problem in MCU and RTC. However, you can see I have used filter capacitors for both MCU and RTC.Two points to check:
1. the I2C pull-up resistors connect to 5V but the MCU is powered from 3.3V so logic high may be excessive for the MCU, better to tie them to a 3.3V supply.
2. The recommended output load resistor (R3) on the LM317 is 240 Ohms, with a higher value you might get some voltage overshoot as it powers up or the load significantly changes.
I would also suggest adding a diode between the input and output pins of both regulators, cathode end to the input, especially on U2 to prevent charge on C2 causing reverse voltage as the input is switched off.
Brian.
Changing diodes and pull-up resistors did not solve the problem.Hi,
read this: https://www.edaboard.com/threads/questions-and-problems-by-ds1307-rtc.409617/post-1766763
Same situation with the ESD diodes, but now it´s the diode(s) inside the microcontroller.
Klaus
DS1307 RTC needs 5v and when it drops Vbat x 1.25 it switches automatically to Vbat(3v). accordingly 5v is necessary. here is the explanation of datasheet in this case:Not only pull-up, also RTC is powered by 5V. Correct logic levels aren't guaranteed with mixed voltage design. I also notice that MCU supply can be switched off while 5V is maintained. Bad idea, asking for trouble.
To understand what's happening in your special test, you can monitor 3.3V and 5V rail. Common 3.3V supply is required anyway.
You did change the ESD diodes? How? Removed the IC plastics, got access to the silicon die and rmeoved the diodes?Changing diodes and pull-up resistors did not solve the problem.
Do you understand that it´s a problem with the signal lines SDA and SCL?DS1307 RTC needs 5v and when it drops Vbat x 1.25 it switches automatically to Vbat(3v).
I have used bypass capacitors for MCU and RTC. Which types of filters can I use?I had heard of this problem from a sub-contractor long ago. I forget the solution.
I sense it is a difference in the -dV/dt with a dry contact removal of DC vs AC slower rate of change with possible bounce. Thus parasitic C and ESR will affect the Vcc vs Vbat ref detection of state change. This suggests filtering should improve the result.
As I mentioned I have already changed them to 3.3 but the problem still remained. If you had any other Idea I would be happy to hear.Do you understand that it´s a problem with the signal lines SDA and SCL?
You may power your DS1303 with 5V - no problem.
But pulling the SDA and SCL to 5V is the problem .. because is clearly violates microcontroller signal input levels.
If you look into the DS1307 datasheet: it says the DS1307 is happy with signal levels of 3.3V. Indeed it says VIH > 2.2V.
--> pull the SDA and SCL up to 3.3V (not 5V)
This solves at least one problem... not necessarily all problems.
Klaus
OMG!!!! I connected the both VDD and VDDA to the same 3.3v, but I provided VDD first then a track from VDD to VDDA. By this explanation after reconnecting 12v power supply MCU gets reset because VDD is provided first then VDDA. Am I right????!!!!Hi,
did you read the microcontroller datasheet:
" VDDA = from V DD to 3.6 V: external analog power supply for ADC, Reset blocks, RCs
and PLL. The VDDA voltage level must be always greater or equal to the V DD voltage
level and must be provided first."
It seems you did not care about this.
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