Recommended values are:

R = 330K

C1 = 33 pF

C2 = 33 pF

Q = 32.8kHz crystal

2 RESULTS

The current consumption in WAIT mode measures the oscillator consumption as long as there

is no additional consumption in the I/O pins with their associated external circuits.

The following table indicates the typical potential current saving in the WAIT mode of the

ST62E2x microcontroller at a temperature of 25 C.

Typical current saving (32kHz crystal)

Standard oscillator

Modified oscillator

5V

A

µ

0

5

4

A

µ

0

0

9

3V

A

µ

5

3

A

µ

0

5

The oscillator start-up time is also increased and ranges from 300 to 500 ms. This is due to the

R, C1 time constant and the normal start-up time of the 32kHz crystal (typically around 250ms).

The use of this additional resistor is made possible by the high gain of the inverter in the ST62

oscillator circuit when working at 32kHz and the characteristics of a standard 32kHz crystal.

Reducing current consumption at 32 kHz with ST62

2/3