Hello All,

We are working with an MSP430F2234 device and we are using P1.2 as an input to detect a switch closure. The external circuitry has a
5 Meg resistor to Vcc being used as a pull up. The switch is normally open and pulls the input node to ground when closed.

We are calculating a current of 300 micro amps through the resistor when the switch is OPEN. We feel that this is a bit high for a
micro that is being touted as very low power. We were expecting the input to be just about near Vcc with therefore practically no current
draw through the 5 Meg resistor. In fact at 300 microamp quiescent current, our batteries will drain in short order.

Is this to be expected or are we perhaps doing something wrong?

Thanks ahead of time to all readers and helpers.

Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529

[Non-text portions of this message have been removed]
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.

> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>
> [Non-text portions of this message have been removed]
> ------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

My appologies to everyone. Really meant to write 0.3 microamps. Is this still in the right ball park? We didn't measure it directly, we just calculated it
by measuring the drop across the resistor.

Thanks.
Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529
----- Original Message -----
From: Redd, Emmett R
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 5:05 PM
Subject: RE: [msp430] MSP430F2234 input current problem
Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.
> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>
> [Non-text portions of this message have been removed]
>
>
> ------------------------------------
>
>
>
>



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

You do not need the MSP430F2234, use a low-power calculator!

--- In m...@yahoogroups.com, "oliver at mettrix" wrote:
>
> My appologies to everyone. Really meant to write 0.3 microamps. Is
this still in the right ball park? We didn't measure it directly, we
just calculated it
> by measuring the drop across the resistor.
>
> Thanks.
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
> ----- Original Message -----
> From: Redd, Emmett R
> To: m...@yahoogroups.com
> Sent: Tuesday, August 19, 2008 5:05 PM
> Subject: RE: [msp430] MSP430F2234 input current problem
> Oliver,
>
> You mention that you are calculating it. How about measuring it?
>
> (BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(
>
> Emmett Redd Ph.D. mailto:EmmettRedd@...
> Professor (417)836-5221
> Department of Physics, Astronomy, and Materials Science
> Missouri State University Fax (417)836-6226
> 901 SOUTH NATIONAL Dept (417)836-5131
> SPRINGFIELD, MO 65897 USA
>
> Physicists always practice energy conservation.
> > -----Original Message-----
> > From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> > On Behalf Of oliver at mettrix
> > Sent: Tuesday, August 19, 2008 4:02 PM
> > To: m...@yahoogroups.com
> > Subject: [msp430] MSP430F2234 input current problem
> >
> > Hello All,
> >
> > We are working with an MSP430F2234 device and we are using
> > P1.2 as an input to detect a switch closure. The external
> > circuitry has a
> > 5 Meg resistor to Vcc being used as a pull up. The switch is
> > normally open and pulls the input node to ground when closed.
> >
> > We are calculating a current of 300 micro amps through the
> > resistor when the switch is OPEN. We feel that this is a bit
> > high for a
> > micro that is being touted as very low power. We were
> > expecting the input to be just about near Vcc with therefore
> > practically no current
> > draw through the 5 Meg resistor. In fact at 300 microamp
> > quiescent current, our batteries will drain in short order.
> >
> > Is this to be expected or are we perhaps doing something wrong?
> >
> > Thanks ahead of time to all readers and helpers.
> >
> > Oliver P. Engel
> > Mettrix Technology Corp
> > 1906 Rt 52 Suite D
> > Hopewell Junction, NY 12533
> >
> > PH: 845 897 4960
> > FX: 845 897 5529
> >
> > [Non-text portions of this message have been removed]
> >
> >
> > ------------------------------------
> >
> >
> >
> >



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

The question is what did you use to measure it? 0.3uA through 5MOhm
is a voltage drop of 1.5V. If you measured from ground to the port
input then the impedance of the meter will pull down the input
depending on the ratio of meter impedance to the pull-up resistor. If
Vcc happens to be 3.0V, then a meter impedance of 5MOhm will cause
such a 1.5V voltage drop (0.3uA is suspiciously close to the current
drawn by the old-style AvoMeters and some low-cost digital meters).
If the meter probes are connected directly across the pull-up
resistor, then it should not be reading 1.5V unless something is
pulsing the port pin into output low.

As a general rule, using a simple pull-up to sense a contact closure
makes no sense, since to get a low current drain when the contact is
closed you have to use a high-impedance pull-up which then exposes
the circuit to pick-up and other noise problems. Far better to use a
much lower pull-up, perhaps 47k instead of 5MOhm, and just drive it
high by another port pin momentarily when you wish to sample the
contact input. Just allow sufficient time for any stray contact
capacitance to charge when the contact is open. Instead of carelessly
throwing away 0.3uA when the contact stays closed the consumption
drops by a few orders of magnitude as well as providing a
noise-resistance low impedance.

Hugh

At 02:38 PM 8/19/2008, you wrote:
My appologies to everyone. Really meant to write 0.3 microamps. Is
this still in the right ball park? We didn't measure it directly, we
just calculated it by measuring the drop across the resistor.

Thanks.
Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529
----- Original Message -----
From: Redd, Emmett R
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 5:05 PM
Subject: RE: [msp430] MSP430F2234 input current problem
Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.
> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>

------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

Thanks for the reply. Actually yes the meter used does affect the reading and taking this into consideration, the result is much better.

With respect to the suggestion that we use an I/O pin to drive the pull up resistor, I would agree that this is a good solution and one that we have used where possible. The problem with this design is that the MSP430 is put into sleep mode and the only signal that is allowed to wake it up is the switch closure, hence detecting the switch closure cannot be done by driving the pull up resistor with an I/O pin. Any suggestions on minimizing the current used under these conditions is of course appreciated.

Oliver
----- Original Message -----
From: Hugh Molesworth
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 6:54 PM
Subject: Re: [msp430] MSP430F2234 input current problem
The question is what did you use to measure it? 0.3uA through 5MOhm
is a voltage drop of 1.5V. If you measured from ground to the port
input then the impedance of the meter will pull down the input
depending on the ratio of meter impedance to the pull-up resistor. If
Vcc happens to be 3.0V, then a meter impedance of 5MOhm will cause
such a 1.5V voltage drop (0.3uA is suspiciously close to the current
drawn by the old-style AvoMeters and some low-cost digital meters).
If the meter probes are connected directly across the pull-up
resistor, then it should not be reading 1.5V unless something is
pulsing the port pin into output low.

As a general rule, using a simple pull-up to sense a contact closure
makes no sense, since to get a low current drain when the contact is
closed you have to use a high-impedance pull-up which then exposes
the circuit to pick-up and other noise problems. Far better to use a
much lower pull-up, perhaps 47k instead of 5MOhm, and just drive it
high by another port pin momentarily when you wish to sample the
contact input. Just allow sufficient time for any stray contact
capacitance to charge when the contact is open. Instead of carelessly
throwing away 0.3uA when the contact stays closed the consumption
drops by a few orders of magnitude as well as providing a
noise-resistance low impedance.

Hugh

At 02:38 PM 8/19/2008, you wrote:
My appologies to everyone. Really meant to write 0.3 microamps. Is
this still in the right ball park? We didn't measure it directly, we
just calculated it by measuring the drop across the resistor.

Thanks.

Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529

----- Original Message -----
From: Redd, Emmett R
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 5:05 PM
Subject: RE: [msp430] MSP430F2234 input current problem

Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.

> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>

[Non-text portions of this message have been removed]
------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

If you can afford LPM3 on a 32kHz crystal then you can use a timer
OUTx signal to do the pull-up work for you with no need to wake up
the cpu and consume power unless the contact happens to be closed.
That should put you down around 1uA or less power consumption for the
MSP430. If you have to use LPM4 (which of course turns off the
crystal) then there are only a few options I can think of.
1) Use a c/o contact with common to the port i/o pin so the pull-up
resistor is never connected to ground
2) Use a slow external oscillator (eg 555 or Nand gate) to drive the pull-up.
3) Do what you do now but add a small low-leakage ceramic capacitor
across the port pin to ground to improve noise rejection.
4) Bootstrap the Vcc to the MSP430 so that it runs at (say) 1.8V in
sleep but switches itself up to 3V or something higher when awake.
Lowering Vcc of course proportionately lowers the current drain (to a
first approximation).

As an aside, most designs I review lose far more leakage current
through Vcc capacitance to ground and Iq from other devices than they
do through correctly running an MSP430 in LPM3. That 10uF Tant you
hang on the analogue 3V rail leaks about 3uA just by itself (though
of course most sensible people use ceramic nowadays).

Hugh

At 07:54 AM 8/20/2008, you wrote:
Thanks for the reply. Actually yes the meter used does affect the
reading and taking this into consideration, the result is much better.

With respect to the suggestion that we use an I/O pin to drive the
pull up resistor, I would agree that this is a good solution and one
that we have used where possible. The problem with this design is
that the MSP430 is put into sleep mode and the only signal that is
allowed to wake it up is the switch closure, hence detecting the
switch closure cannot be done by driving the pull up resistor with an
I/O pin. Any suggestions on minimizing the current used under these
conditions is of course appreciated.

Oliver
----- Original Message -----
From: Hugh Molesworth
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 6:54 PM
Subject: Re: [msp430] MSP430F2234 input current problem
The question is what did you use to measure it? 0.3uA through 5MOhm
is a voltage drop of 1.5V. If you measured from ground to the port
input then the impedance of the meter will pull down the input
depending on the ratio of meter impedance to the pull-up resistor. If
Vcc happens to be 3.0V, then a meter impedance of 5MOhm will cause
such a 1.5V voltage drop (0.3uA is suspiciously close to the current
drawn by the old-style AvoMeters and some low-cost digital meters).
If the meter probes are connected directly across the pull-up
resistor, then it should not be reading 1.5V unless something is
pulsing the port pin into output low.

As a general rule, using a simple pull-up to sense a contact closure
makes no sense, since to get a low current drain when the contact is
closed you have to use a high-impedance pull-up which then exposes
the circuit to pick-up and other noise problems. Far better to use a
much lower pull-up, perhaps 47k instead of 5MOhm, and just drive it
high by another port pin momentarily when you wish to sample the
contact input. Just allow sufficient time for any stray contact
capacitance to charge when the contact is open. Instead of carelessly
throwing away 0.3uA when the contact stays closed the consumption
drops by a few orders of magnitude as well as providing a
noise-resistance low impedance.

Hugh

At 02:38 PM 8/19/2008, you wrote:
My appologies to everyone. Really meant to write 0.3 microamps. Is
this still in the right ball park? We didn't measure it directly, we
just calculated it by measuring the drop across the resistor.

Thanks.

Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529

----- Original Message -----
From: Redd, Emmett R
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 5:05 PM
Subject: RE: [msp430] MSP430F2234 input current problem

Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.

> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>

------------------------------------



(You need to be a member of msp430 -- send a blank email to msp430-subscribe@yahoogroups.com )

I forgot to add that on the 2xxx in sleep mode you can always switch
to the VLO instead of the external crystal, saving a little more
power. I think that only applies to LPM3 and not LPM4, though. It
would be nice to be able to (say) run just the watchdog off the VLO
in LPM4, but I don't think that is an option. Might be worth checking.

Hugh

At 09:31 AM 8/20/2008, you wrote:
If you can afford LPM3 on a 32kHz crystal then you can use a timer
OUTx signal to do the pull-up work for you with no need to wake up
the cpu and consume power unless the contact happens to be closed.
That should put you down around 1uA or less power consumption for the
MSP430. If you have to use LPM4 (which of course turns off the
crystal) then there are only a few options I can think of.
1) Use a c/o contact with common to the port i/o pin so the pull-up
resistor is never connected to ground
2) Use a slow external oscillator (eg 555 or Nand gate) to drive the pull-up.
3) Do what you do now but add a small low-leakage ceramic capacitor
across the port pin to ground to improve noise rejection.
4) Bootstrap the Vcc to the MSP430 so that it runs at (say) 1.8V in
sleep but switches itself up to 3V or something higher when awake.
Lowering Vcc of course proportionately lowers the current drain (to a
first approximation).

As an aside, most designs I review lose far more leakage current
through Vcc capacitance to ground and Iq from other devices than they
do through correctly running an MSP430 in LPM3. That 10uF Tant you
hang on the analogue 3V rail leaks about 3uA just by itself (though
of course most sensible people use ceramic nowadays).

Hugh

At 07:54 AM 8/20/2008, you wrote:
Thanks for the reply. Actually yes the meter used does affect the
reading and taking this into consideration, the result is much better.

With respect to the suggestion that we use an I/O pin to drive the
pull up resistor, I would agree that this is a good solution and one
that we have used where possible. The problem with this design is
that the MSP430 is put into sleep mode and the only signal that is
allowed to wake it up is the switch closure, hence detecting the
switch closure cannot be done by driving the pull up resistor with an
I/O pin. Any suggestions on minimizing the current used under these
conditions is of course appreciated.

Oliver
----- Original Message -----
From: Hugh Molesworth
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 6:54 PM
Subject: Re: [msp430] MSP430F2234 input current problem
The question is what did you use to measure it? 0.3uA through 5MOhm
is a voltage drop of 1.5V. If you measured from ground to the port
input then the impedance of the meter will pull down the input
depending on the ratio of meter impedance to the pull-up resistor. If
Vcc happens to be 3.0V, then a meter impedance of 5MOhm will cause
such a 1.5V voltage drop (0.3uA is suspiciously close to the current
drawn by the old-style AvoMeters and some low-cost digital meters).
If the meter probes are connected directly across the pull-up
resistor, then it should not be reading 1.5V unless something is
pulsing the port pin into output low.

As a general rule, using a simple pull-up to sense a contact closure
makes no sense, since to get a low current drain when the contact is
closed you have to use a high-impedance pull-up which then exposes
the circuit to pick-up and other noise problems. Far better to use a
much lower pull-up, perhaps 47k instead of 5MOhm, and just drive it
high by another port pin momentarily when you wish to sample the
contact input. Just allow sufficient time for any stray contact
capacitance to charge when the contact is open. Instead of carelessly
throwing away 0.3uA when the contact stays closed the consumption
drops by a few orders of magnitude as well as providing a
noise-resistance low impedance.

Hugh

At 02:38 PM 8/19/2008, you wrote:
My appologies to everyone. Really meant to write 0.3 microamps. Is
this still in the right ball park? We didn't measure it directly, we
just calculated it by measuring the drop across the resistor.

Thanks.

Oliver P. Engel
Mettrix Technology Corp
1906 Rt 52 Suite D
Hopewell Junction, NY 12533

PH: 845 897 4960
FX: 845 897 5529

----- Original Message -----
From: Redd, Emmett R
To: m...@yahoogroups.com
Sent: Tuesday, August 19, 2008 5:05 PM
Subject: RE: [msp430] MSP430F2234 input current problem

Oliver,

You mention that you are calculating it. How about measuring it?

(BTW, 300 micro amps through a 5 Mohm resistor is 1500 V. :-(

Emmett Redd Ph.D. mailto:E...@missouristate.edu
Professor (417)836-5221
Department of Physics, Astronomy, and Materials Science
Missouri State University Fax (417)836-6226
901 SOUTH NATIONAL Dept (417)836-5131
SPRINGFIELD, MO 65897 USA

Physicists always practice energy conservation.

> -----Original Message-----
> From: m...@yahoogroups.com [mailto:m...@yahoogroups.com]
> On Behalf Of oliver at mettrix
> Sent: Tuesday, August 19, 2008 4:02 PM
> To: m...@yahoogroups.com
> Subject: [msp430] MSP430F2234 input current problem
>
> Hello All,
>
> We are working with an MSP430F2234 device and we are using
> P1.2 as an input to detect a switch closure. The external
> circuitry has a
> 5 Meg resistor to Vcc being used as a pull up. The switch is
> normally open and pulls the input node to ground when closed.
>
> We are calculating a current of 300 micro amps through the
> resistor when the switch is OPEN. We feel that this is a bit
> high for a
> micro that is being touted as very low power. We were
> expecting the input to be just about near Vcc with therefore
> practically no current
> draw through the 5 Meg resistor. In fact at 300 microamp
> quiescent current, our batteries will drain in short order.
>
> Is this to be expected or are we perhaps doing something wrong?
>
> Thanks ahead of time to all readers and helpers.
>
> Oliver P. Engel
> Mettrix Technology Corp
> 1906 Rt 52 Suite D
> Hopewell Junction, NY 12533
>
> PH: 845 897 4960
> FX: 845 897 5529
>

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