5/7

s

The charging time is mainly controlled through the capacitor value. But if the capacitor value

is increased beyond 1uF, although the interval between external interrupts (in ms) is

increased, the capacitor itself consumes more current while charging. Hence, the average

consumption is high in this case. A summary of the consumption and the external interrupt

even though the external interrupt interval is longer than in Tables 2 & 3, the consumption is

higher.

If a different hardware setup is used, where an external series R (to generate the external in-

terrupt through an external RC combination) is connected, the capacitor charging time de-

creases drastically. For example, when a series R of 490K is added, the charging time de-

creases to 6.7µs. Hence, the period the MCU stays in Halt mode is very small, causing more

consumption.

As a conclusion, the best result (minimum consumption) is achieved with a 1µF capacitor

value and using an internal pullup. This is illustrated in Figure 3.

the two different capacitor values (Cext = 1.0 uF and 0.47uF) used for the active RC.

Setup

No.

C= 2.2µF

C= 4.7µF

Consumption in

power saving

mode

Ext Interrupt

Interval (ms)

Consumption in

Power saving

mode

Ext Interrupt

Interval. (ms)

1

3.0

35.6

171.6

48.9

200.0

2

4.0

86.4

107.6

114.5

124.2

3

5.0

146.6

83.6

189.6

97.2