Hello all,
On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups
enabled on reset. I would therefore expect the voltage measured on any of those
pins to be my power supply voltage, 3.3V. However, on my device, I'm
measuring just over 2V on all of my unused input pins. The device is working
perfectly fine otherwise. When the pins are set to outputs, they do correctly
swing to 3.3V. Is this normal or do I have a dud chip?
Amr
LPC17xx: Voltage on input pin when pull-up is enabled
Started by ●April 12, 2011
Reply by ●April 12, 20112011-04-12
--- In l..., "amr_mt_bekhit" wrote:
>
> Hello all,
>
> On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
>
> Amr
>
I get 2.120V on the GPIO pins after reset and that is normal. When GPIO are set as outputs I get 3.093V, also normal. Your chip is fine.
>
> Hello all,
>
> On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
>
> Amr
>
I get 2.120V on the GPIO pins after reset and that is normal. When GPIO are set as outputs I get 3.093V, also normal. Your chip is fine.
Reply by ●April 12, 20112011-04-12
Hi,
It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
Regards,
Daniel
----- Reply message -----
From: "amr_mt_bekhit"
To:
Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
Date: Tue, Apr 12, 2011 23:19
Hello all,
On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
Amr
Yahoo! Groups Links
It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
Regards,
Daniel
----- Reply message -----
From: "amr_mt_bekhit"
To:
Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
Date: Tue, Apr 12, 2011 23:19
Hello all,
On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
Amr
Yahoo! Groups Links
Reply by ●April 12, 20112011-04-12
--- In l..., "d...@yahoo.com" wrote:
>
> Hi,
>
> It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
>
> If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
>
> Regards,
> Daniel
>
> ----- Reply message -----
> From: "amr_mt_bekhit"
> To:
> Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
> Date: Tue, Apr 12, 2011 23:19
> Hello all,
>
> On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
>
> Amr
>
>
>
> Hi,
>
> It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
>
> If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
>
> Regards,
> Daniel
>
> ----- Reply message -----
> From: "amr_mt_bekhit"
> To:
> Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
> Date: Tue, Apr 12, 2011 23:19
> Hello all,
>
> On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
>
> Amr
>
>
Reply by ●April 13, 20112011-04-13
The datasheet in Fig.12 indicates a 0.3V drop from the 3.3V supply for the
pullup. It still does not explain the extra 1V drop, unless you load the pin
"excessively" (read: 10s of uA , i.e. a load in the order of 100kOhm). Also,
according to the DC params table, there is a considerable tolerance in the
pullup's current.
JW
>
> --- In l..., "d...@yahoo.com" wrote:
> >
> > Hi,
> >
> > It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
> >
> > If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
> >
> > Regards,
> > Daniel
> >
> > ----- Reply message -----
> > From: "amr_mt_bekhit"
> > To:
> > Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
> > Date: Tue, Apr 12, 2011 23:19
> >
> >
> > Hello all,
> >
> > On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
JW
>
> --- In l..., "d...@yahoo.com" wrote:
> >
> > Hi,
> >
> > It's normal. The internal pull up in input mode is not good enough to pull the pin to VDD.
> >
> > If you put active low LED (1 pin to the VDD 1 pin to the input pin) on the pulled up input pins, you'll see that it's still glow although it's quite dim.
> >
> > Regards,
> > Daniel
> >
> > ----- Reply message -----
> > From: "amr_mt_bekhit"
> > To:
> > Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is enabled
> > Date: Tue, Apr 12, 2011 23:19
> >
> >
> > Hello all,
> >
> > On the LPC17xx family, the GPIO pins are configured as inputs with the pull-ups enabled on reset. I would therefore expect the voltage measured on any of those pins to be my power supply voltage, 3.3V. However, on my device, I'm measuring just over 2V on all of my unused input pins. The device is working perfectly fine otherwise. When the pins are set to outputs, they do correctly swing to 3.3V. Is this normal or do I have a dud chip?
Reply by ●April 13, 20112011-04-13
JW,
Daniel's post was orfaned from Amr's original thread and we should
probably all move back to that thread and let this one die.
See my post in Amr's original thread:
http://tech.groups.yahoo.com/group/lpc2000/message/53693
I measured the input pins with a multimeter and no loads on the pins. I
agree that it doesn't explain the extra 1V drop, but that is what the
inputs are after a reset. The output pin I measured was also driving an
led so was a little lower in voltage than an unloaded output.
Larry
--- In l..., Jan Waclawek wrote:
>
> The datasheet in Fig.12 indicates a 0.3V drop from the 3.3V supply for
the pullup. It still does not explain the extra 1V drop, unless you load
the pin "excessively" (read: 10s of uA , i.e. a load in the order of
100kOhm). Also, according to the DC params table, there is a
considerable tolerance in the pullup's current.
>
> JW
> >
> > --- In l..., "daniel.widyanto@..."
daniel.widyanto@ wrote:
> > >
> > > Hi,
> > >
> > > It's normal. The internal pull up in input mode is not good enough
to pull the pin to VDD.
> > >
> > > If you put active low LED (1 pin to the VDD 1 pin to the input
pin) on the pulled up input pins, you'll see that it's still glow
although it's quite dim.
> > >
> > > Regards,
> > > Daniel
> > >
> > > ----- Reply message -----
> > > From: "amr_mt_bekhit" amrbekhit@
> > > To: l...
> > > Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is
enabled
> > > Date: Tue, Apr 12, 2011 23:19
> > >
> > >
> > > Hello all,
> > >
> > > On the LPC17xx family, the GPIO pins are configured as inputs with
the pull-ups enabled on reset. I would therefore expect the voltage
measured on any of those pins to be my power supply voltage, 3.3V.
However, on my device, I'm measuring just over 2V on all of my unused
input pins. The device is working perfectly fine otherwise. When the
pins are set to outputs, they do correctly swing to 3.3V. Is this normal
or do I have a dud chip?
>
Daniel's post was orfaned from Amr's original thread and we should
probably all move back to that thread and let this one die.
See my post in Amr's original thread:
http://tech.groups.yahoo.com/group/lpc2000/message/53693
I measured the input pins with a multimeter and no loads on the pins. I
agree that it doesn't explain the extra 1V drop, but that is what the
inputs are after a reset. The output pin I measured was also driving an
led so was a little lower in voltage than an unloaded output.
Larry
--- In l..., Jan Waclawek wrote:
>
> The datasheet in Fig.12 indicates a 0.3V drop from the 3.3V supply for
the pullup. It still does not explain the extra 1V drop, unless you load
the pin "excessively" (read: 10s of uA , i.e. a load in the order of
100kOhm). Also, according to the DC params table, there is a
considerable tolerance in the pullup's current.
>
> JW
> >
> > --- In l..., "daniel.widyanto@..."
daniel.widyanto@ wrote:
> > >
> > > Hi,
> > >
> > > It's normal. The internal pull up in input mode is not good enough
to pull the pin to VDD.
> > >
> > > If you put active low LED (1 pin to the VDD 1 pin to the input
pin) on the pulled up input pins, you'll see that it's still glow
although it's quite dim.
> > >
> > > Regards,
> > > Daniel
> > >
> > > ----- Reply message -----
> > > From: "amr_mt_bekhit" amrbekhit@
> > > To: l...
> > > Subject: [lpc2000] LPC17xx: Voltage on input pin when pull-up is
enabled
> > > Date: Tue, Apr 12, 2011 23:19
> > >
> > >
> > > Hello all,
> > >
> > > On the LPC17xx family, the GPIO pins are configured as inputs with
the pull-ups enabled on reset. I would therefore expect the voltage
measured on any of those pins to be my power supply voltage, 3.3V.
However, on my device, I'm measuring just over 2V on all of my unused
input pins. The device is working perfectly fine otherwise. When the
pins are set to outputs, they do correctly swing to 3.3V. Is this normal
or do I have a dud chip?
>
Reply by ●April 13, 20112011-04-13
Reply by ●April 13, 20112011-04-13
Thank you for the link;)
Zero, hi, is that you?
--- In l..., "zero_atwork" wrote:
>
> This is a known hardware effect, descibed in #10 of
>
> http://knowledgebase.nxp.com/showthread.php?t81
>
Zero, hi, is that you?
--- In l..., "zero_atwork" wrote:
>
> This is a known hardware effect, descibed in #10 of
>
> http://knowledgebase.nxp.com/showthread.php?t81
>
Reply by ●April 13, 20112011-04-13
"zero_atwork" wrote:
>
> This is a known hardware effect, descibed in #10 of
>
> http://knowledgebase.nxp.com/showthread.php?t81
> I just heard back from NXP directly on this issue.
> According to NXP, the internal pull-up is provided by a FET configured as a current source.
> As a result, the maximum pull-up voltage will be around 0.7V less than Vdd_IO.
> The GPIO are designed this way to provide 5V tolerance.
Ah, and is this a different NXP than the one I have the datasheet from? Surely they know the difference between 0.7V and 0.3V, however "typical" the figure in question is.
Morever, I tried to subtract 0.7V from 3.3V and I somehow can't get 2.3V (from the post the link leads to) nor 2.1V measured by Larry (who's right in that even a crappy DMM wouldn't sink currents in the order of 10uA).
I don't think this issue can be simply passed on with a couple of handwaves.
Could somebody from NXP listening here please explain these discrepancies in a binding way?
Thanks,
Jan Waclawek
>
> This is a known hardware effect, descibed in #10 of
>
> http://knowledgebase.nxp.com/showthread.php?t81
> I just heard back from NXP directly on this issue.
> According to NXP, the internal pull-up is provided by a FET configured as a current source.
> As a result, the maximum pull-up voltage will be around 0.7V less than Vdd_IO.
> The GPIO are designed this way to provide 5V tolerance.
Ah, and is this a different NXP than the one I have the datasheet from? Surely they know the difference between 0.7V and 0.3V, however "typical" the figure in question is.
Morever, I tried to subtract 0.7V from 3.3V and I somehow can't get 2.3V (from the post the link leads to) nor 2.1V measured by Larry (who's right in that even a crappy DMM wouldn't sink currents in the order of 10uA).
I don't think this issue can be simply passed on with a couple of handwaves.
Could somebody from NXP listening here please explain these discrepancies in a binding way?
Thanks,
Jan Waclawek
Reply by ●April 14, 20112011-04-14
I have made a measurement on a completely unloaded pin of the LPC1768 specimen I
have here and posted the results in
http://f1.grp.yahoofs.com/v1/gKmmTdhR5uPJKTGBBFAFdX2qlt1UlTPCZttVLzwvgvaBJ01NrhafHXKDbzyY0RnCvvJOIopkyud4zKogs5-4CAuCxG_83g/LPC17XX/LPC%20pullup%20measurement.pdf
. The load was a 200kOhm potentiometer in series with a fixed 10kOhm resistor
used as current sense. I see little reason not to extrapolate the graph at the
low current portion, which would give me around 2.2V at 0uA (I actually measured
2.283V on an otherwise unloaded pin). I used a commonplace DMM, so there may be
a couple of mV of absolute error and the input impedance might have been a
couple of MOhms (adding a fraction of uA current).
The most disturbing fact is, that the pullup does not seem to have any overhead in ensuring a valid log 1 input, as it barely reaches the specified VINH(min) = 0.7*VDD.
Jan Waclawek
PS. Sorry for breaking the thread, due to thread-agnostic e-mail clients I am using
Original thread: http://tech.groups.yahoo.com/group/lpc2000/message/53693
The first spin-off thread: http://tech.groups.yahoo.com/group/lpc2000/message/53696
The most disturbing fact is, that the pullup does not seem to have any overhead in ensuring a valid log 1 input, as it barely reaches the specified VINH(min) = 0.7*VDD.
Jan Waclawek
PS. Sorry for breaking the thread, due to thread-agnostic e-mail clients I am using
Original thread: http://tech.groups.yahoo.com/group/lpc2000/message/53693
The first spin-off thread: http://tech.groups.yahoo.com/group/lpc2000/message/53696
