Power Consumption with Input NOT at Rail

[paulrbryson]

Posted on February 02, 2016 at 23:22

I am using the STM8S103K3.  The data specifies power consumption only with all inputs at the rail voltage.  Also the data sheet says to ''turn off schmitt input'' on adc input to save power.  These things imply that excess power is consumed by digital inputs when not at the supply rails. 

My PWM outputs are tied to Vcc/2. When I turn them off how much power will be consumed by the input being at Vcc/2.  If I drive the output to one of the rails this will also consume power.  So I have to choose one or the other ... or add circuitry.

[paulrbryson]

Posted on August 13, 2016 at 23:13

I think that I found a solution:

a. set the pin as output (this turns off the schmitt input circuitry)

b. set the output to pseudo open drain

c. set the output state to ''high''

In theory this should allow the pin to float to intermediate voltages without consuming

excess supply current (delta Icc) - BUT I have not tested it.

[paulrbryson]

Posted on August 14, 2016 at 02:29

This is embarrassing. I misinterpreted the diagram.

Setting the pin to output mode does NOT disable the input circuits.

So I guess there is no way to avoid the ΔIcc current - the magnitude of which

is not specified in the datasheet.