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AP2141 issue

  • Thread starter Marco Trapanese
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Marco Trapanese

Jan 1, 1970
0
I'm using a AP2141:

http://www.diodes.com/datasheets/AP2141_51.pdf

to disconnect a circuit from another.
It is connected as following:

IN 4V
EN 5V
OUT 10k pull-down (for test purpose)

On the OUT pin I read the same voltage applied to the IN pin, 4V.
I checked it really is an AP2141 (active low).

I can't understand why I read 4V instead of 0V.
There are several boards on my desk, all with the same behavior.

Perhaps I misunderstood something in the ds?

Thanks!
Marco
 
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Marco Trapanese

Jan 1, 1970
0
Il 06/04/2013 19:40, Jim Thompson ha scritto:
Unless your "load" draws some current greater than the switch leakage
it will show input voltage.


I connected a 180 ohm resistor across output terminals...

You DO have the 2141, Enable=LOW, not the 2151, Enable=HIGH ?


Unless the label on the package is wrong, I do have a 2141 ;)

Marco
 
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Marco Trapanese

Jan 1, 1970
0
Il 06/04/2013 21:59, Jim Thompson ha scritto:
Is it legal for EN > IN?


There is no mention of the contrary on the ds.

I also note "All IN pins must be tied together externally" and "All
OUT pins must be tied together externally"


I noticed that too ;) I tied them toghther.

Maybe you have the "frog" problem.... croak >:-}


Two "frog" problems on a single board! Double croak :(

Marco
 
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Marco Trapanese

Jan 1, 1970
0
Il 06/04/2013 21:01, Marco Trapanese ha scritto:
Unless the label on the package is wrong, I do have a 2141 ;)


Very strange.
Some other tests:

1) I disconnected the outputs and the enable pins from the circuit.
Loaded the output ones with a 1k resistor.

Powered the board and after that I forced the voltage on the enable pin
with a piece of wire. It works opposite: applying a high level leads to
conduct (output voltage = input voltage). Bring the enable down to zero
volt disconnect the load (output voltage = 0V).

With 4V at input I can rise the enable voltage up to 5V without any problem.


2) I changed my board adding an n-mos to invert the enable signal. But
again it doesn't switch off even with 0V on the enable pin. I removed
the mos and did again the test with the wire *after* power up and it
works (anyway like 2151).


Bottom line: I'm afraid the datasheet doesn't tell the truth also this
time. I can't understand at all the polarity of the enable signal. The
figure 1 at page 6 is very clear though.
Perhaps there are some timings to respect at power up. I suspect because
the enable voltage will rise before the input, it may likely latch in
some undesirable condition.

Marco
 
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Marco Trapanese

Jan 1, 1970
0
Il 07/04/2013 17:01, Jamie ha scritto:
Maybe you need a pull down R on the input pin?


Do you mean the enable pin? Or the voltage input pin?
If you're talking about the enable pin at first I had a pull-down
resistor, then I used a mos to tie to gnd the enable pin.

Marco
 
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Jamie

Jan 1, 1970
0
Marco said:
Il 06/04/2013 21:01, Marco Trapanese ha scritto:




Very strange.
Some other tests:

1) I disconnected the outputs and the enable pins from the circuit.
Loaded the output ones with a 1k resistor.

Powered the board and after that I forced the voltage on the enable pin
with a piece of wire. It works opposite: applying a high level leads to
conduct (output voltage = input voltage). Bring the enable down to zero
volt disconnect the load (output voltage = 0V).

With 4V at input I can rise the enable voltage up to 5V without any
problem.


2) I changed my board adding an n-mos to invert the enable signal. But
again it doesn't switch off even with 0V on the enable pin. I removed
the mos and did again the test with the wire *after* power up and it
works (anyway like 2151).


Bottom line: I'm afraid the datasheet doesn't tell the truth also this
time. I can't understand at all the polarity of the enable signal. The
figure 1 at page 6 is very clear though.
Perhaps there are some timings to respect at power up. I suspect because
the enable voltage will rise before the input, it may likely latch in
some undesirable condition.

Marco
Maybe you need a pull down R on the input pin?

Jamie
 
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Marco Trapanese

Jan 1, 1970
0
Il 07/04/2013 19:52, Joe Chisolm ha scritto:
Verify your parts. You said in another post that you had
tied the inputs together so you must be using a SOP or MSOP
package. The part number is on the top. In this case dont
trust the package label.


I'm talking about the marks on the case. Shall I trust them?

Measure your EN voltage, make sure it's below 0.8V or above 2V


I measured 4 mV and about 5V. But I tried also from 3V with an external
power supply.

Marco
 
J

Jamie

Jan 1, 1970
0
Marco said:
Il 07/04/2013 17:01, Jamie ha scritto:




Do you mean the enable pin? Or the voltage input pin?
If you're talking about the enable pin at first I had a pull-down
resistor, then I used a mos to tie to gnd the enable pin.

Marco
Looking at the data sheet, which I just did, your device P.N. is
designated to be active in the low state. This means you should
have a pull UP not DOWN, R on the EN input. And pulling the EN
pin low via the processor or a open collector/Drain device with
pull up R still attached should work.

Jamie
 
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Marco Trapanese

Jan 1, 1970
0
Il 07/04/2013 22:46, Jamie ha scritto:
Looking at the data sheet, which I just did, your device P.N. is
designated to be active in the low state. This means you should
have a pull UP not DOWN, R on the EN input. And pulling the EN
pin low via the processor or a open collector/Drain device with
pull up R still attached should work.


Perhaps I didn't explain well.
I have a pull-down because I want the device is ON by default.
When I plug an external power supply the enable pin will be forced to 5V.

I'd expect the device will disconnect its load.
But it doesn't happen, the load is still connected.

Inverting the logic, that is pull up the enable pin to turn on the
device and tie to 0V to disconnect the load will work only if I power
the board first and *after* I toggle the pin.

Marco
 
M

Marco Trapanese

Jan 1, 1970
0
Il 08/04/2013 16:49, Jim Thompson ha scritto:
Oooops! That can be tricky... did you make yourself a latch?


I've just ripped off those switches... and I make the boards work using
standard mosfet :)

Marco
 
J

Jamie

Jan 1, 1970
0
Marco said:
Il 07/04/2013 22:46, Jamie ha scritto:




Perhaps I didn't explain well.
I have a pull-down because I want the device is ON by default.
When I plug an external power supply the enable pin will be forced to 5V.

I'd expect the device will disconnect its load.
But it doesn't happen, the load is still connected.

Inverting the logic, that is pull up the enable pin to turn on the
device and tie to 0V to disconnect the load will work only if I power
the board first and *after* I toggle the pin.

Marco
I think you picked the wrong part to use, it looks like a one shot
switch. Which is common in power management start up systems because
you only need to do this once. In other words, it latched in. To turn
off such a device, you need to kill the front end, which is doable via
a pmos being reversed biased from the uC for example.

Jamie
 
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