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Discussion - MCU / Re: RTC on FT90x revision C
« on: April 18, 2020, 12:12:50 PM »
Hello
thanks for the replies.
My goal is to keep RTC alive for at least 20 days without power.
The capacitor has some advantages over the battery. Simple and fast charging circuit and above all, it has no discharge problems during storage after the board has been assembled inside the product container. For this I would like more information on the mysterious PIN VBAT for CPU FT90x C. From BRT's answer I understand that the VBAT of the FT90x works in the same way as FT93x. Is this so? In this case, is VBAT pin the only RTC power source? In the AN_004 solution is declared the current when power on is under 1 uA and backup current 9 uA. This seems unlikely because in the TI datasheet (http://www.ti.com/lit/ds/symlink/sn74auc2g53.pdf) because the VCC consumption of the chip alone is 10uA at 2.7V
In your previous version B chip and MM900EV1A (see attachment) you put MCP7940N. You can see the backup current in the figure in attachment. Don't you have a similar test for VBAT pin of FT90x?
I found a good comparison between different backup power source in this related AN:
http://ww1.microchip.com/downloads/en/Appnotes/00002027A.pdf
If we want to seriously use the FT90x also as RTC can you offer the details to design the VBAT circuit? or do you advise me to continue using an external RTC?
thanks for the replies.
My goal is to keep RTC alive for at least 20 days without power.
The capacitor has some advantages over the battery. Simple and fast charging circuit and above all, it has no discharge problems during storage after the board has been assembled inside the product container. For this I would like more information on the mysterious PIN VBAT for CPU FT90x C. From BRT's answer I understand that the VBAT of the FT90x works in the same way as FT93x. Is this so? In this case, is VBAT pin the only RTC power source? In the AN_004 solution is declared the current when power on is under 1 uA and backup current 9 uA. This seems unlikely because in the TI datasheet (http://www.ti.com/lit/ds/symlink/sn74auc2g53.pdf) because the VCC consumption of the chip alone is 10uA at 2.7V
In your previous version B chip and MM900EV1A (see attachment) you put MCP7940N. You can see the backup current in the figure in attachment. Don't you have a similar test for VBAT pin of FT90x?
I found a good comparison between different backup power source in this related AN:
http://ww1.microchip.com/downloads/en/Appnotes/00002027A.pdf
If we want to seriously use the FT90x also as RTC can you offer the details to design the VBAT circuit? or do you advise me to continue using an external RTC?