Nxp Semiconductors PCA8565 用户手册

 

 

UM10301_1 

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For some applications low power consumption is a key requirement. Power consumption 
can be minimized by applying several measures: 

•  Select PCF8563 (I

2

C) or PCF2123 (SPI-bus). The PCF2123 has the lowest power 

consumption which is further decreased when a crystal is selected that has a load 
capacitance of 7 pF instead of the more standard 12.5 pF (a lower load capacitance 
results in a lower power consumption, but not all RTCs allow to select a crystal that 
requires a C

L

 in that range); 

•  Select a crystal with a low motional resistance. The higher the resistance the higher 

the losses. For lowest power consumption, aim to find a crystal with R

1

 < 40 kΩ; 

•  The timer source clock frequency influences power consumption which is highest at 

4096 Hz. The difference in power consumption between the other three clock 
frequencies is negligible; 

•  Use lowest possible V

DD

. See the application examples given in Fig 18 and Fig 19. 

During normal operation a diode charges a super cap of for example 0.47 F or 1 F. 
During standby the RTC is supplied by this super cap. General purpose small signal 
diodes may have leakage currents in the order of magnitude of the current 
consumption of these low power RTCs. In order to maximize the RTC backup time it 
is advisable to select a low leakage current diode. See section 13.4;