Lpc2000

First of all a happy and successful New Year to everybody!

There have been some questions about 5V tolerance of analog pins.
All device on the market before the LPC2130 series can not tolerate 5V
on any pin that is configured or can be configured as analog input pin.
Starting with the LPC2130 series, pins that are not configured as
analog inputs (but could be) will no longer have a negative effect on
the ADC result. 
Please keep in mind that the pin 0.25 DAC output is not 5V tolerant
even  if used as digital I/O.  The effect will be that it starts
sinking current if not externally limited to the bitter end of thermal
destruction. So at the very least limit the current if you expect more
than Vdd on that pin.

Another question was there about 3.3V being up and running while 5V
are connected to some I/O pins. If you generate the 3.3V off the 5V
input using a voltage regulator, the delay will be short to have 3.3V
after 5V, in fact it might actually be at 3.3V before the voltage
reaches 5V externally. The important issue is that during a longer
period of time with a pin externally driven up to 5V and no Vdd for
the microcontroller, there will be stress to the gate oxide and sooner
or later the device will die. So, don't do that but do not worry about
a 3.3V voltage generated from a 5V during power up. 

Hope I did not add to the confusion but answered to some of your concerns.

Off to a good start, Robert

Hi,

a follow up to my own message. I got additional information on the
3.3V / 5V tolerance issue. 
The e-mail that I got lets me quantify the time with 5V being present
while Vdd3 not being present at all (0V). Assuming the difference of
the two voltages is actually 5V, the expected lifetime of that
particular pin is several days. Let's assume a very slow regulator
following the 5V with 10 ms delay, this would result in > 1Mio power
on cycles for just 1 day of that expected lifetime. 
In a nutshell, this is nothing to worry about. 

Robert

> Another question was there about 3.3V being up and running while 5V
> are connected to some I/O pins. If you generate the 3.3V off the 5V
> input using a voltage regulator, the delay will be short to have 3.3V
> after 5V, in fact it might actually be at 3.3V before the voltage
> reaches 5V externally. The important issue is that during a longer
> period of time with a pin externally driven up to 5V and no Vdd for
> the microcontroller, there will be stress to the gate oxide and sooner
> or later the device will die. So, don't do that but do not worry about
> a 3.3V voltage generated from a 5V during power up. 
>

The LPC213x User Manual contains the following Note in Table 143:

"Note: if the A/D converter is used, signal levels on analog input 
pins must not be above the level of V3A at any time. Otherwise, A/D 
converter readings will be invalid."

Are you saying that the User Manual is wrong?


--- In lpc2000@yahoogroups.com, "philips_apps" <philips_apps@y...> 
wrote:
> 
> First of all a happy and successful New Year to everybody!
> 
> There have been some questions about 5V tolerance of analog pins.
> All device on the market before the LPC2130 series can not tolerate 
5V
> on any pin that is configured or can be configured as analog input 
pin.
> Starting with the LPC2130 series, pins that are not configured as
> analog inputs (but could be) will no longer have a negative effect 
on
> the ADC result. 
> Please keep in mind that the pin 0.25 DAC output is not 5V tolerant
> even  if used as digital I/O.  The effect will be that it starts
> sinking current if not externally limited to the bitter end of 
thermal
> destruction. So at the very least limit the current if you expect 
more
> than Vdd on that pin.
> 
> Another question was there about 3.3V being up and running while 5V
> are connected to some I/O pins. If you generate the 3.3V off the 5V
> input using a voltage regulator, the delay will be short to have 
3.3V
> after 5V, in fact it might actually be at 3.3V before the voltage
> reaches 5V externally. The important issue is that during a longer
> period of time with a pin externally driven up to 5V and no Vdd for
> the microcontroller, there will be stress to the gate oxide and 
sooner
> or later the device will die. So, don't do that but do not worry 
about
> a 3.3V voltage generated from a 5V during power up. 
> 
> Hope I did not add to the confusion but answered to some of your 
concerns.
> 
> Off to a good start, Robert

Ed see below

if you still have open questions I will do my best to answer them 

Robert


--- In lpc2000@yahoogroups.com, "edmiller613" <edmiller613@y...> wrote:
> 
> The LPC213x User Manual contains the following Note in Table 143:
> 
> "Note: if the A/D converter is used, signal levels on analog input 
> pins must not be above the level of V3A at any time. Otherwise, A/D 
> converter readings will be invalid."
> 
> Are you saying that the User Manual is wrong?
> 

In all devices with ADCs before the LPC2130 series, a signal >Vdd on
any pin "that could be used as analog input" screws up the ADC even if
it is defined as digital input. On the LPC2130 series the digital
input can now exceed Vdd. If the input is configured as analog input
you violate the spec (results in ADC wrong results) if exceeding Vdd.
Summary: if 5V on an analog input pin -> results corrupted, if 5V on a
pin that could be analog in but is configured as digital in -> no
corruption 

Confused?  Everything clear?

> 
> --- In lpc2000@yahoogroups.com, "philips_apps" <philips_apps@y...> 
> wrote:
> > 
> > First of all a happy and successful New Year to everybody!
> > 
> > There have been some questions about 5V tolerance of analog pins.
> > All device on the market before the LPC2130 series can not tolerate 
> 5V
> > on any pin that is configured or can be configured as analog input 
> pin.
> > Starting with the LPC2130 series, pins that are not configured as
> > analog inputs (but could be) will no longer have a negative effect 
> on
> > the ADC result. 
> > Please keep in mind that the pin 0.25 DAC output is not 5V tolerant
> > even  if used as digital I/O.  The effect will be that it starts
> > sinking current if not externally limited to the bitter end of 
> thermal
> > destruction. So at the very least limit the current if you expect 
> more
> > than Vdd on that pin.
> > 
> > Another question was there about 3.3V being up and running while 5V
> > are connected to some I/O pins. If you generate the 3.3V off the 5V
> > input using a voltage regulator, the delay will be short to have 
> 3.3V
> > after 5V, in fact it might actually be at 3.3V before the voltage
> > reaches 5V externally. The important issue is that during a longer
> > period of time with a pin externally driven up to 5V and no Vdd for
> > the microcontroller, there will be stress to the gate oxide and 
> sooner
> > or later the device will die. So, don't do that but do not worry 
> about
> > a 3.3V voltage generated from a 5V during power up. 
> > 
> > Hope I did not add to the confusion but answered to some of your 
> concerns.
> > 
> > Off to a good start, Robert

Your explanation is clear as glass.

Thanks,
Ed

P.S.: The User Manual is wrong, or confusing at best.  It says:

"Note that these analog inputs are always connected to their pins, 
even if the Pin Multiplexing Register assigns them to port pins."

That seems to imply that the affect that applying 5V to these pins 
will have on the A/D converter is not be dependent on the setting of 
the Pin Multiplexing Register.

Also:

"If the A/D converter is not used in an application then the pins 
associated with A/D inputs can be used as 5V tolerant digital IO pins"

This says to me that you can only use them for 5V if the A/D 
converter "is not used."  However, if the converter is used, but some 
pins (with 5V) are mapped as i/o, there will still be a problem.


--- In lpc2000@yahoogroups.com, "philips_apps" <philips_apps@y...> 
wrote:
> 
> Ed see below
> 
> if you still have open questions I will do my best to answer them 
> 
> Robert
> 
> 
> --- In lpc2000@yahoogroups.com, "edmiller613" <edmiller613@y...> 
wrote:
> > 
> > The LPC213x User Manual contains the following Note in Table 143:
> > 
> > "Note: if the A/D converter is used, signal levels on analog 
input 
> > pins must not be above the level of V3A at any time. Otherwise, 
A/D 
> > converter readings will be invalid."
> > 
> > Are you saying that the User Manual is wrong?
> > 
> 
> In all devices with ADCs before the LPC2130 series, a signal >Vdd on
> any pin "that could be used as analog input" screws up the ADC even 
if
> it is defined as digital input. On the LPC2130 series the digital
> input can now exceed Vdd. If the input is configured as analog input
> you violate the spec (results in ADC wrong results) if exceeding 
Vdd.
> Summary: if 5V on an analog input pin -> results corrupted, if 5V 
on a

> pin that could be analog in but is configured as digital in -> no
> corruption 
> 
> Confused?  Everything clear?
>