Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the
circuitry inside the pin. I have a feeling I have seen it in the datasheet/user
manual but now cannot find it. Or I might be thinking of Atmel AVR.
I really just want to know what protection diodes are on the pins and how they
are connected - I am curious about what happens when you put 5V on the 5V
tolerant pins and if there is any current drain down to 3v3.
--
Tim Mitchell
pin schematic for lpc17xx
Started by ●July 18, 2012
Reply by ●July 18, 20122012-07-18
Not exactly a schematics, but Ili (input leakage current) in Table 7 of the
LPC17xx datasheet is specified at Vi=5V to be typ 10uA max 22uA; whereas at
Vi=3.3V it is typ 2uA max 4uA.
JW
----- Original Message ---------------
>Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
>
>I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
>
>--
>Tim Mitchell
>
JW
----- Original Message ---------------
>Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
>
>I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
>
>--
>Tim Mitchell
>
Reply by ●July 30, 20122012-07-30
I've just been skimming for the same thing. There's not much to look
at, on page 105 of the LPC178X_7X.pdf datasheet under Application information.
It lists ESD protection in the diagram, but gives no real data to what voltage
they clamp to.
I was wondering if the inputs were at all protected in case of signal overshoots or undershoots. Still haven't found any decent information.
Regards,
Matt
--- In l..., "Tim Mitchell" wrote:
>
> Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
>
> I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
>
> --
> Tim Mitchell
>
I was wondering if the inputs were at all protected in case of signal overshoots or undershoots. Still haven't found any decent information.
Regards,
Matt
--- In l..., "Tim Mitchell" wrote:
>
> Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
>
> I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
>
> --
> Tim Mitchell
>
Reply by ●July 30, 20122012-07-30
Why not just measure it?
Put some kind of current limiting resistor in series with the pin and drive the voltage high enough to get 5V at the pin. You can measure the voltage drop across the resistor and determine the input current.
Do the same thing for 0V but stay within the spec at the pin. Again, you can easily measure the current.
Be aware that 5V tolerance only applies to pins operating in GPIO mode (or, more probably, not A/D mode).
Personally, I take a page from FPGA interfacing and put a 330 ohm resistor in series with IO pins if they aren't dedicated to a 3.3V gadget. This limits the current (somewhat) for 5V inputs, doesn't interfere with outputs (generally) and protects against user error.
Richard
--- In l..., "teeysensei" wrote:
>
> I've just been skimming for the same thing. There's not much to look at, on page 105 of the LPC178X_7X.pdf datasheet under Application information. It lists ESD protection in the diagram, but gives no real data to what voltage they clamp to.
>
> I was wondering if the inputs were at all protected in case of signal overshoots or undershoots. Still haven't found any decent information.
>
> Regards,
> Matt
>
> --- In l..., "Tim Mitchell" wrote:
> >
> > Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
> >
> > I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
> >
> > --
> > Tim Mitchell
>
Put some kind of current limiting resistor in series with the pin and drive the voltage high enough to get 5V at the pin. You can measure the voltage drop across the resistor and determine the input current.
Do the same thing for 0V but stay within the spec at the pin. Again, you can easily measure the current.
Be aware that 5V tolerance only applies to pins operating in GPIO mode (or, more probably, not A/D mode).
Personally, I take a page from FPGA interfacing and put a 330 ohm resistor in series with IO pins if they aren't dedicated to a 3.3V gadget. This limits the current (somewhat) for 5V inputs, doesn't interfere with outputs (generally) and protects against user error.
Richard
--- In l..., "teeysensei" wrote:
>
> I've just been skimming for the same thing. There's not much to look at, on page 105 of the LPC178X_7X.pdf datasheet under Application information. It lists ESD protection in the diagram, but gives no real data to what voltage they clamp to.
>
> I was wondering if the inputs were at all protected in case of signal overshoots or undershoots. Still haven't found any decent information.
>
> Regards,
> Matt
>
> --- In l..., "Tim Mitchell" wrote:
> >
> > Has anyone seen anywhere a GPIO pin schematic for the LPC17xx devices, i.e. the circuitry inside the pin. I have a feeling I have seen it in the datasheet/user manual but now cannot find it. Or I might be thinking of Atmel AVR.
> >
> > I really just want to know what protection diodes are on the pins and how they are connected - I am curious about what happens when you put 5V on the 5V tolerant pins and if there is any current drain down to 3v3.
> >
> > --
> > Tim Mitchell
>
