MSP430F6435: Large RTCB error issue

Cherry Zhou

Part Number: MSP430F6435

NOTE: 5ppm 32.768K crystal for XT1, the VBAT pin is connected to a 3-V rechargeable coin cell battery.

Issue：

The interference and wiring issues are eliminated, various matching capacitors are tried, and the error is still large. Some are 1-hour errors of about 1 second, and some are 2-hour errors of 1 second.

And the customer has tried the following methods:

1.The accuracy is better if the MCU does not go into the sleep LPM3 state and remains active.

2.Set BAKDIS in BAKCTL to 1 for better accuracy. However, the backup battery cannot be used after the power down.

The customer would like to know if there are better ways to achieve it.

Thanks!

Best Regards,

Cherry Zhou

over 4 years ago

0 Urica Wang over 4 years ago

TI__Intellectual 2650 points

Hi Cherry,

I found this app report on using the MSP430 RTC_B module with battery backup [link]. Section 2.2 "RTC_B Oscillator Fault" mentions that if there's a fault on the XT1 supplying the RTC (where a fault could mean that the crystal stops or oscillates at the wrong frequency), the RTC calendar time may not be correct. Section 3.5 "Oscillator Fault Handling" goes into more details on how to catch and deal with these RTC oscillator faults. Could the customer try implementing the described solution to see if the error decreases?

Thanks,

Urica Wang

0 Cherry Zhou over 4 years ago in reply to Urica Wang

TI__Mastermind 22235 points

Hi Urica,

Thanks for your reply!

And the customer also would like to know if LPM3 mode will cause a fault.

Thanks again!

Best Regards,

Cherry

0 Urica Wang over 4 years ago in reply to Cherry Zhou

TI__Intellectual 2650 points

Hi Cherry,

Looking at the Real-Time Clock B module in the User Guide https://www.ti.com/lit/slau208, it doesn't look like LPM3 will cause a fault in the RTC_B module.

Thanks,

Urica Wang

**Attention** This is a public forum

MSP low-power microcontrollers

MSP low-power microcontroller forum

MSP430F6435: Large RTCB error issue