Hi everybody:
I am building some kind of datalogger and, to save power, I try to cut the Vcc of the others IC using a MOSFET topology as a switch for the V regulator of the ICs (7805 Vin pin) and putting the micro in Idle mode. I think the FET part is OK because I copy it from a book ("The art of electronics").
The problem is that the ICs are still consuming current after the open of the transistor switch.
I am not sure if I connected something wrong or, as said in the ADC datasheet, I need a buffer for each IC bus port to not overload the bus when they are shutted down, or something else.
With the power connected everything seems to work fine.
The 8052 micro receive the data sharing the port 0 as a bus with a 32 kB parallel memory, a 573 buffer for latching the address and a ADC0804 A/D converter. First, I didn´t use a pull up resistor, then I put 10k ohm, but the problem persist.
Checking the voltages, it seems that the power came from the port0(e.g., at the 7805, Vout is larger than Vin).
My questions are:
It is port0 in high impedance with the sentence mov p0,#0ffh? So why the current can escape?
Are the pull up resistors neccesary? How can I calculate them?
Anybody knows another way to cut the power for the ICs?