LPC MicrocontrollersのトピックRe: LPC1768 RTC issue

LPC1768 RTC issue

yogesh20 — Sat, 13 May 2023 11:39:16 GMT

We have use LPC1768 micro controller in our product,

issue observed as per below,

1) RTC increment issue (same board RTC not working),

(touch figure 32khz crystal or capacitor and RTC is working fine)

Same as touch any oscilloscope probe to capacitor RTC working fine.

but same board power on instrument RTC not working.

What is issue?

Kindly guide us to resolve this issue.

Re: LPC1768 RTC issue

xiangjun_rong — Mon, 15 May 2023 08:53:08 GMT

Hi,

As you said that the RTC works fine after you touch the crystal or capacitor, I suppose that the crystal or capacitor are not soldered reliably, or the capacitor value is not appropriate.

Pls consult the crystal manufacturer to get the capacitor value the crystal required, then use the formula to get the actual capacitor value.

For the following formula, Although it is based on LPC546xx, it adapts to the LPC17xx.

Hope it can help you

XiangJun Rong

Re: LPC1768 RTC issue

yogesh20 — Mon, 15 May 2023 09:10:25 GMT

Dear XiangJun Rong thanks for update,

this issue only some board,

We have use 32.768Khz and capacitor value us 12pf. we resolder LPC1769 and crystal, but issue still same.

Re: LPC1768 RTC issue

xiangjun_rong — Mon, 15 May 2023 09:17:41 GMT

Hi,

is it convenient to post the crystal part number data sheet so that we can compute the capacitor value?

XiangJun Rong

Re: LPC1768 RTC issue

yogesh20 — Mon, 15 May 2023 09:23:22 GMT

830002995B
use this part

Re: LPC1768 RTC issue

xiangjun_rong — Mon, 15 May 2023 09:31:43 GMT

Hi,

Okay, i have checked the required load capacitance is 12.5pF for the crystal, so the actual capacitor should be:

Cx1=Cx2=2*12.5-(3+1)=21pF.capacitor

Pls try to use two about 21pF capacitor for the crystal.

XiangJun Rong

Re: LPC1768 RTC issue

yogesh20 — Mon, 15 May 2023 11:15:24 GMT

Ok thanks for update ,

we will check and update you.

Re: LPC1768 RTC issue

yogesh20 — Mon, 22 May 2023 04:49:24 GMT

Under testing..