LPC1788: High current consumption at VBAT pin.

[robertmolnar]

I use LPC1788FBD208 chip, firmware use RTC with backup battery (3 V lithium), MCI (SD card), SPI, 2 UART modules. Sometime I find that the I(VBAT) goes to 55 mA and stay constant even power off state and deep power-down state too. At first time I think it is a chip hard fault (ESD), I replace them. But tomorrow I found a chip, which first time worked I(VBAT) = 1uA, then fault I(VBAT) = 55 mA, then again worked I(VBAT) = 1 uA.

Someone had seen this phenomenon? This may be a firmware problem?

[Carlos_Mendoza]

Hi Robert,

There is an IBAT errata for these devices that mentions that IBAT current could go as high as about 10 uA when only VBAT is applied, but it is not near the 55mA you mention:

http://www.nxp.com/documents/errata_sheet/ES_LPC177X_8X.pdf 

So I believe there is a hardware problem, make sure there are no damaged diodes or a short circuit somewhere in your design.

Hope it helps!

Best Regards,
Carlos Mendoza
Technical Support Engineer

[ZhangTao1212]

Or it can be said that when the LPC1788 enters the deep power - down mode before shutting down, and then the instrument is powered on again, it cannot be awakened from the deep power - down mode. According to the LPC1788 specification, the deep power - down mode can only be awakened by an external RESET or an RTC interrupt. However, the normal power - on of the instrument does not fall into the above two cases.

[ZhangTao1212]

Hi Carlos

We have used LPC1788 in our product. During the production process, there is a certain proportion of cases where Ibat is too high (using an external CR2032 battery), and it is about 10uA when there is an abnormality. According to your suggestion, I used BOD and entered the deep power-down mode before the instrument was turned off. However, in this case, when there is an external CR2032 battery, the instrument cannot work properly when I turn it on again. It seems that it has not completely exited the deep power-down mode. When I unplug the external battery, the instrument can be powered on and work normally. May I ask what causes this situation and how should I deal with it?

thank you for your help.

[ZhangTao1212]

Hi Carlos

We have used LPC1788 in our product. During the production process, there is a certain proportion of cases where Ibat is too high (using an external CR2032 battery), and it is about 10uA when there is an abnormality. According to your suggestion, I used BOD and entered the deep power-down mode before the instrument was turned off. However, in this case, when there is an external CR2032 battery, the instrument cannot work properly when I turn it on again. It seems that it has not completely exited the deep power-down mode. When I unplug the external battery, the instrument can be powered on and work normally. May I ask what causes this situation and how should I deal with it?

thank you for your help.

[robertmolnar]

Hi Carlos,

Thank you for your suggestion!

Yes I read this errata, and try it. It doesn't resolve the problem.

Now it seems to hardware problem, but I don't know what can cause it.

Best regards,

Robert Molnar