0
\$\begingroup\$

I have an IC that is activated when pulsing a pin high, the pin should be keep floating after the pulse. The circuit is powered using a battery, and that IC then wake up everything else (Regulator, MCU, etc).

I'm looking for something like this:

Battery -> Pulse to the pin -> IC wakes up -> IC wakes up everything else

I'm trying to guess how to do that in simple terms, I mean without adding even more complexity to the circuit.

I have tried bridging the pin to the + of the battery manually for a moment (< 1 sec) and it works, but only after removing the + from the pin.

So the question is: How do I create a brief pulse using simple components? It is possible?

\$\endgroup\$
  • \$\begingroup\$ Can you give a link to the datasheet for this IC? \$\endgroup\$ – The Photon Jun 16 '13 at 0:46
2
\$\begingroup\$

The difficult bit is keeping the pin 'floating' afterwards. I offer this as a possible solution.

enter image description here When the circuit is switched on the voltage across C1 cannot change immediately so that the negative terminal is pulled up to the supply voltage (leading edge). R1 gives a path for the capacitor to charge and the voltage across R1 will fall with time. After 1 CR time constant this voltage will be approximately 1/3 of the supply.

Q1 will initially be turned ON but as the capacitor charges the voltage across R1 falls. Q1 will be turned OFF after a short period of time.

The diode is in there for when the power is switched off.

When Q1 is turned ON Q2 is also turned ON as the voltage at its gate will fall near to 0 across R2. This will pull up the RESET pin to the positive rail for the short time period set by C1 R1.

After Q1 (and Q2) are turned OFF there is no connection to the RESET and so the pin will be floating.

\$\endgroup\$

Not the answer you're looking for? Browse other questions tagged or ask your own question.