Hello,
reading the ds I'm not sure if this two ICs:
when turned of using the enable pin can withstand a voltage (3.3V) on their output. The input voltage may change from 0V to 4.7V.
Thanks Marco
The way I read the data, VSHDN > 45% of VIN to activate the circuit.
As for "withstanding", I'd hazard a guess that the input has a series resistor built-in, poly on oxide, so no junction forwards to fret over. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Il 17/03/2013 19:51, Jim Thompson ha scritto:
Hi Jim! Let's suppose the VSHDN is pulled down to 0V. The circuit is off.
Well, I was afraid about the mosfet body diode: if I have a voltage at output and 0V on the input will it turn on? Even the IC is in off condition.
Marco
Aha! You're asking a different question than I assumed. You wonder about the case where you have commanded shutdown (\SHDN\=0), and VIN=0, but there's a voltage _forced_ at the output?
The block diagram of your first device implies a body-diode problem... though that doesn't necessarily have to be the case... I've designed "body drivers" to cope with such events (sort of like bus drivers when powered down.
The second chip, a switch, implies an N-channel switch.
Who knows? Test yourself for current flow and the magic smoke ;-) ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Il 17/03/2013 20:15, Jim Thompson ha scritto:
Exactly! I'm sorry again for my poor English!
LOL :)
In the first case I solved placing another diode at the input so there is no return path.
For the second chip.... I found another one:
which is designed to avoid the problem.
Marco
Much better than my Italian ;-) Though I can "speak" a little Latin
On most processes, use of a P-channel pass device makes it easy... since it has its own tub, you drive the tub with the higher of VIN or VOUT.... so you can survive an output voltage even when the chip is unpowered. ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et |
Il 17/03/2013 20:34, Jim Thompson ha scritto:
Good point. Anyway I changed a bit the connections and I avoided the problem at all.
Thank you again, Jim.
Marco
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