Floating analog inputs

[web55604]

Posted on July 06, 2005 at 17:16

Floating analog inputs

[web55604]

Posted on July 05, 2005 at 12:13

Hi

I am using an ST72F324 with analog inputs on port D

When in power down mode, the input to these ports can be an arbritary value.

This causes the digital input buffer to consume power - up to 200 microamps.

Is there any way to switch this off ?

Are the input buffers isolated only when ADC conversion takes place ?

[alok2]

Posted on July 06, 2005 at 02:22

As recommended in the datasheet, there shall not be any floating inputs. It is adviced to put a pull-up or pull-dn on these pins.

What do you mean by power-dn mode ? BTW, PortD pins do not have external interrupt capability. Yu can try reducing power consumption by enabling the internal pull-up.

[web55604]

Posted on July 06, 2005 at 17:16

Port D is multiplexed with the ADC analog inputs.

They may be driven by an arbritary analog value.

If this is done, the P and N transistors of the inputs buffer may both saturate leading to a higher power consumption.

The device is powered down in full HALT mode.

I am also using an external low voltage detact device (device LVT disabled) and real time clock/alarm, so the total system drain is around 6 uA. The target is