Good morning,
I have a problem with power consumption of LPC54618 RTC. As illustrated in attached PDF I have a board with the configuration visible on the schematic. Battery is a rechargeable Panasonic VL-1220 with 7mA/h current capacitance. LPC54618 datasheet reports that, in power off conditions (board off, with only VBAT present), consumption is 340nA. I can't measure precisely the consumption, but after several tests, I see that the current absorbed from RTC is more than that indicated. I tried to left reset pin floating ad suggested in the datasheet, but without significative differences (and how can I left floating a reset pin?!?!). I have 2 different boards with same LPC54618 RTC circuit and same problem.
Is there anyone that can help me to understand how solve this problem?
For information I used same battery on LPC1768 controller (that has similar consumption characteristics) without problems and duration about 6 months.
Many thanks in advance for any information.
Best regards,
Marco Di Biaggio
Hi, Marco,
I suggest you use a precise Multi Meter Instrument to test the RTC pin current with VDD=VDDA=VREFP=GND, you can not figure out the RTC current by battery energy consumption for a fixed time, because the battery has large leakage current, in other words, battery consumes power itself.
Hope it can help you
BR
XiangJun Rong
Hi XiangJun Rong,
thanks for your reply.
I measured the current that flows on JP13 (with board not powered) and it is 34.6uA (microampere).
If I disconnect R33 current absorbtion is about 0.3uA. But, how can i leave floating a RESET pin?? Datasheet says that there is an internal pull-up, but I would feel more comfortable with an external reset supervisor.
So, how could I connect the MCP809 to avoid current consumption?
Thanks in advance for any response.
Best regards,
Marco
Hi, Marco,
The Resetn pin floating means that there is not any connection on the pin Resetn or any driven signal.
I have checked your prb_Battery_r0.pdf file, if you connect the MCP809, when the MCP809 is power off, you can not guarantee that the /RST pin of MCP809 is float in the case.
As an alternative, if you replace the R33 with a diode, what is the result? I am not sure if it can solve your issue with a diode, pls have a try.
BR
XiangJun Rong