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MSP430F2012 - analog voltage at IO/ADC pin while device is unpowered

Started by Aaron Greer April 8, 2008
I've come across a strange behavior in my current design.
Under certain conditions the MSP430 is un-powered, but there is an analog signal on one or more IO/ADC pins. I can measure a current (5-10uA) entering the MSP430 pin and apparently leaving the VCC pin. One explanation I can think of is that the internal ESD protection devices are forward biased and conducting out the VCC pin. The other part of the story is that after the MSP experiences this condition, I begin to see unexpected behavior (with the device powered) on the IO/ADC pins which had the analog voltages present. For instance, the internal pull up or pull down resistors seem to be enabled (which one seems random), when I'm certain I've disabled them in my application code. Can you please provide some insight regarding any adverse affects of powering the IO/ADC pins with the MSP un-powered? Do you think there may be a problem with this that is causing the strange pull up/down behavior? Do you expect doing this would decrease the lifespan of the MSP devices?

thanks,
Aaron

Beginning Microcontrollers with the MSP430

Aaron Greer wrote:
> I've come across a strange behavior in my current design.
> Under certain conditions the MSP430 is un-powered, but there is an analog signal on one or more IO/ADC pins. I can measure a current (5-10uA) entering the MSP430 pin and apparently leaving the VCC pin. One explanation I can think of is that the internal ESD protection devices are forward biased and conducting out the VCC pin. The other part of the story is that after the MSP experiences this condition, I begin to see unexpected behavior (with the device powered) on the IO/ADC pins which had the analog voltages present. For instance, the internal pull up or pull down resistors seem to be enabled (which one seems random), when I'm certain I've disabled them in my application code. Can you please provide some insight regarding any adverse affects of powering the IO/ADC pins with the MSP
> un-powered? Do you think there may be a problem with this that is causing the strange pull up/down behavior? Do you expect doing this would decrease the lifespan of the MSP devices?
>
> thanks,
> Aaron
>
>
Is there a reason you cannot just place the MSP430 into LPM3 or LPM4 and
leave the power on / not in reset?

Thanks,

Jim

_____

From: m... [mailto:m...] On Behalf Of
Aaron Greer
Sent: Tuesday, April 08, 2008 1:21 PM
To: m...
Subject: Re: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin while
device is unpowered

Yes, I am realizing how much of a bad idea this was.
Right now, I have an externally generated signal which disables the 3.3V
supply going to the MSP. Perhaps I will take the signal and connect it to
the nRST pin of the MSP and leave the 3.3V supply on all the time. Do you
have any idea what to expect if I held the MSP in reset while the analog
signals are connected to the ADC pins?

thanks,
Aaron

----- Original Message -----
From: "old_cow_yellow"
yahoo.com>
To: msp430@yahoogroups. com
Sent: Tuesday, April 8, 2008 11:09:59 AM (GMT-0700) America/Denver
Subject: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin while
device is unpowered

I think you should have put F2012 in LPM4 instead of removing Vcc.
Without Vcc, it is not a good idea to have any signal on any pin.

--- In msp430@yahoogroups. com , Aaron
Greer wrote:
>
> I've come across a strange behavior in my current design.
> Under certain conditions the MSP430 is un-powered, but there is an
analog signal on one or more IO/ADC pins. I can measure a current
(5-10uA) entering the MSP430 pin and apparently leaving the VCC pin.
One explanation I can think of is that the internal ESD protection
devices are forward biased and conducting out the VCC pin. The other
part of the story is that after the MSP experiences this condition, I
begin to see unexpected behavior (with the device powered) on the
IO/ADC pins which had the analog voltages present. For instance, the
internal pull up or pull down resistors seem to be enabled (which one
seems random), when I'm certain I've disabled them in my application
code. Can you please provide some insight regarding any adverse
affects of powering the IO/ADC pins with the MSP un-powered? Do you
think there may be a problem with this that is causing the strange
pull up/down behavior? Do you expect doing this would decrease the
lifespan of the MSP devices?
>
> thanks,
> Aaron
>




I do not know the answer. But I think it is not desirable either.

(a) For some earlier MSP430, the current consumption is very high when
nRST is low. F2012 may or may not have this problem.

(b) nRST being low may change all port pins to digital input pins (POR
state). If they are connected to analog voltage, that may cause
oscillation or excessive current consumption too.

--- In m..., Aaron Greer wrote:
>
> Yes, I am realizing how much of a bad idea this was.
> Right now, I have an externally generated signal which disables the
3.3V supply going to the MSP. Perhaps I will take the signal and
connect it to the nRST pin of the MSP and leave the 3.3V supply on all
the time. Do you have any idea what to expect if I held the MSP in
reset while the analog signals are connected to the ADC pins?
>
> thanks,
> Aaron
>
> ----- Original Message -----
> From: "old_cow_yellow"
> To: m...
> Sent: Tuesday, April 8, 2008 11:09:59 AM (GMT-0700) America/Denver
> Subject: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin
while device is unpowered
>
> I think you should have put F2012 in LPM4 instead of removing Vcc.
> Without Vcc, it is not a good idea to have any signal on any pin.
>
> --- In m... , Aaron Greer wrote:
> >
> > I've come across a strange behavior in my current design.
> > Under certain conditions the MSP430 is un-powered, but there is an
> analog signal on one or more IO/ADC pins. I can measure a current
> (5-10uA) entering the MSP430 pin and apparently leaving the VCC pin.
> One explanation I can think of is that the internal ESD protection
> devices are forward biased and conducting out the VCC pin. The other
> part of the story is that after the MSP experiences this condition, I
> begin to see unexpected behavior (with the device powered) on the
> IO/ADC pins which had the analog voltages present. For instance, the
> internal pull up or pull down resistors seem to be enabled (which one
> seems random), when I'm certain I've disabled them in my application
> code. Can you please provide some insight regarding any adverse
> affects of powering the IO/ADC pins with the MSP un-powered? Do you
> think there may be a problem with this that is causing the strange
> pull up/down behavior? Do you expect doing this would decrease the
> lifespan of the MSP devices?
> >
> > thanks,
> > Aaron
> >
>

Did you consider using a fet switch going into the A/D input in series
instead of a resistor? Look at Fairchild FSA4159P6X

Thanks,

Jim

_____

From: m... [mailto:m...] On Behalf Of
Aaron Greer
Sent: Tuesday, April 08, 2008 2:18 PM
To: m...
Subject: Re: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin while
device is unpowered

Hmmm... that does not sound pleasant. I am planning to place a 200K series
resistor going into the ADC pin, maybe that will cut down on some of this
behavior.

Does anyone know about the 2012 current consumption with nRST low?

thanks!
Aaron

----- Original Message -----
From: "old_cow_yellow"
yahoo.com>
To: msp430@yahoogroups. com
Sent: Tuesday, April 8, 2008 11:55:56 AM (GMT-0700) America/Denver
Subject: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin while
device is unpowered

I do not know the answer. But I think it is not desirable either.

(a) For some earlier MSP430, the current consumption is very high when
nRST is low. F2012 may or may not have this problem.

(b) nRST being low may change all port pins to digital input pins (POR
state). If they are connected to analog voltage, that may cause
oscillation or excessive current consumption too.

--- In msp430@yahoogroups. com , Aaron
Greer wrote:
>
> Yes, I am realizing how much of a bad idea this was.
> Right now, I have an externally generated signal which disables the
3.3V supply going to the MSP. Perhaps I will take the signal and
connect it to the nRST pin of the MSP and leave the 3.3V supply on all
the time. Do you have any idea what to expect if I held the MSP in
reset while the analog signals are connected to the ADC pins?
>
> thanks,
> Aaron
>
> ----- Original Message -----
> From: "old_cow_yellow"
> To: msp430@yahoogroups. com
> Sent: Tuesday, April 8, 2008 11:09:59 AM (GMT-0700) America/Denver
> Subject: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin
while device is unpowered
>
> I think you should have put F2012 in LPM4 instead of removing Vcc.
> Without Vcc, it is not a good idea to have any signal on any pin.
>
> --- In msp430@yahoogroups. com , Aaron
Greer wrote:
> >
> > I've come across a strange behavior in my current design.
> > Under certain conditions the MSP430 is un-powered, but there is an
> analog signal on one or more IO/ADC pins. I can measure a current
> (5-10uA) entering the MSP430 pin and apparently leaving the VCC pin.
> One explanation I can think of is that the internal ESD protection
> devices are forward biased and conducting out the VCC pin. The other
> part of the story is that after the MSP experiences this condition, I
> begin to see unexpected behavior (with the device powered) on the
> IO/ADC pins which had the analog voltages present. For instance, the
> internal pull up or pull down resistors seem to be enabled (which one
> seems random), when I'm certain I've disabled them in my application
> code. Can you please provide some insight regarding any adverse
> affects of powering the IO/ADC pins with the MSP un-powered? Do you
> think there may be a problem with this that is causing the strange
> pull up/down behavior? Do you expect doing this would decrease the
> lifespan of the MSP devices?
> >
> > thanks,
> > Aaron
> >
>




Yes, I am realizing how much of a bad idea this was.
Right now, I have an externally generated signal which disables the 3.3V supply going to the MSP. Perhaps I will take the signal and connect it to the nRST pin of the MSP and leave the 3.3V supply on all the time. Do you have any idea what to expect if I held the MSP in reset while the analog signals are connected to the ADC pins?

thanks,
Aaron

----- Original Message -----
From: "old_cow_yellow"
To: m...
Sent: Tuesday, April 8, 2008 11:09:59 AM (GMT-0700) America/Denver
Subject: [msp430] Re: MSP430F2012 - analog voltage at IO/ADC pin while device is unpowered

I think you should have put F2012 in LPM4 instead of removing Vcc.
Without Vcc, it is not a good idea to have any signal on any pin.

--- In m... , Aaron Greer wrote:
>
> I've come across a strange behavior in my current design.
> Under certain conditions the MSP430 is un-powered, but there is an
analog signal on one or more IO/ADC pins. I can measure a current
(5-10uA) entering the MSP430 pin and apparently leaving the VCC pin.
One explanation I can think of is that the internal ESD protection
devices are forward biased and conducting out the VCC pin. The other
part of the story is that after the MSP experiences this condition, I
begin to see unexpected behavior (with the device powered) on the
IO/ADC pins which had the analog voltages present. For instance, the
internal pull up or pull down resistors seem to be enabled (which one
seems random), when I'm certain I've disabled them in my application
code. Can you please provide some insight regarding any adverse
affects of powering the IO/ADC pins with the MSP un-powered? Do you
think there may be a problem with this that is causing the strange
pull up/down behavior? Do you expect doing this would decrease the
lifespan of the MSP devices?
>
> thanks,
> Aaron
>