双电源给RTC供电方案

Dual Power supply application for RTC PT7C43390

Application circuit:

Use this application circuit, when first power on, there maybe cause two different status. One

F i r s t p o w e r o n b ) :

M a y b e c a u s e p o w e r r e s e t f a i l u r e

。。。

power line (was shown in wave1) and the undershot on RTC VDD pin (see wave2):

Improved initialization flow for dual power supply with PT7C43390:

1) If the POC =1 or BLD =1, the RTC need to initialize.

2) If the POC ≠1 and BLD≠1, Add judge the Free register.

If the Free register ≠“01010101” the RTC need to initialize.

3) Write “1” to reset flag, reset the RTC timer register.

4) Write “01010101” to free register.

Note:

1)Use free register as judgment register to avoid the power on

reset failure.

2)Power on reset failure only occurs the first time RTC power up.

Improved application circuits for dual power supply:

In some case when VDD power up, the dithering of building in battery will cause the pulse or undershot on power line.

C1 and C2 can make the wave of VDD_RTC smoothly. The test wave of VDD_RTC is as follow,

Using these circuits can eliminate the dithering with less than 5 seconds width. The probability of occurrence of Power on reset failure will be very small.