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I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to 5V with say 10K, to satisfy the input reqmts of the driver? And secondly, I cant find a list anywhere in the datasheets of the LPC pins which are 5V tolerant, I notice some are specified as 3.3V + 0.6V but I cant figure out which ones, can anyone help please. Michael. |
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5V tolerant i/o pins
Started by ●March 4, 2004
Reply by ●March 5, 20042004-03-05
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onceinfour wrote: > I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid > drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to 5V > with say 10K, to satisfy the input reqmts of the driver? Hmmm. You might be able to do that with a diode, to prevent it from back-feeding current into the internal 3.3v line from the 5v line when it's trying to pull the line high. On the other hand, there is a neat circuit to bidirectionally convert between logic levels, I seem to recall... put a MOSFET between the 3.3v part and the 5v line (as in, drain to source) and connect the gate of the FET to 3.3v, or somesuch. I found the circuit while googling for ways of communicating between 3.3v and 5v I2C. I'm planning on putting 5v pullups on the I2C lines from the LPC - but they're pull-down-only, so that's meant to be OK. > Michael. ABS |
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Reply by ●March 5, 20042004-03-05
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Michael, All the IO pins on that device are 5V tolerant EXCEPT any that can be configured as an ADC input. This is lacking in the documentation and will be remedied. In future devices the analog pins will also be 5V tolerant. Philips Apps. --- In , "onceinfour" <mmack287@h...> wrote: > I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid > drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to 5V > with say 10K, to satisfy the input reqmts of the driver? > And secondly, I cant find a list anywhere in the datasheets of the > LPC pins which are 5V tolerant, I notice some are specified as 3.3V + > 0.6V but I cant figure out which ones, can anyone help please. > Michael. |
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Reply by ●March 5, 20042004-03-05
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Please, need an element of practicality here. We are talking about a lot of i/o lines, in our design we are looking at 3 x 8 way solenoid drivers, that's 24 signals. Would make more sense to use a 3.3V to 5V logic translator(s), but I am trying to save the board space and cost. Michael. --- In , Alaric B Snell <alaric@a...> wrote: > onceinfour wrote: > > I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid > > drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to 5V > > with say 10K, to satisfy the input reqmts of the driver? > > Hmmm. You might be able to do that with a diode, to prevent it from > back-feeding current into the internal 3.3v line from the 5v line when > it's trying to pull the line high. > > On the other hand, there is a neat circuit to bidirectionally convert > between logic levels, I seem to recall... put a MOSFET between the 3.3v > part and the 5v line (as in, drain to source) and connect the gate of > the FET to 3.3v, or somesuch. I found the circuit while googling for > ways of communicating between 3.3v and 5v I2C. > > I'm planning on putting 5v pullups on the I2C lines from the LPC - but > they're pull-down-only, so that's meant to be OK. > > > Michael. > > ABS |
Reply by ●March 5, 20042004-03-05
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On Fri, 05 Mar 2004 13:22:37 +0000, Alaric B Snell wrote: onceinfour wrote: > I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid > drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to 5V > with say 10K, to satisfy the input reqmts of the driver? Hmmm. You might be able to do that with a diode, to prevent it from back-feeding current into the internal 3.3v line from the 5v line when it's trying to pull the line high. On the other hand, there is a neat circuit to bidirectionally convert between logic levels, I seem to recall... put a MOSFET between the 3.3v part and the 5v line (as in, drain to source) and connect the gate of the FET to 3.3v, or somesuch. I found the circuit while googling for ways of communicating between 3.3v and 5v I2C. I'm planning on putting 5v pullups on the I2C lines from the LPC - but they're pull-down-only, so that's meant to be OK. > Michael. ABS ===================================================================== IDT <www.idt.com> make a product line called QuickSwitch which uses this technique. They are bi-directional and fast. Regards -Bill Knight R O SoftWare |
Reply by ●March 5, 20042004-03-05
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I suppose this is for the Philips Apps. OK all pins except a/d are 5V tolerant. What level (in the high state) will I get on a pin configured as an output if I have a pullup to 5V, and what current will it draw. Sorry to harp on, but I need to know what voltage level I can generate for my peripheral device, and what size of pull-up I can use. Michael. --- In , "philips_apps" <philips_apps@y...> wrote: > Michael, > All the IO pins on that device are 5V tolerant EXCEPT any that can > be configured as an ADC input. This is lacking in the documentation > and will be remedied. In future devices the analog pins will also be > 5V tolerant. > > Philips Apps. > --- In , "onceinfour" <mmack287@h...> wrote: > > I want to connect the LPC2114 (or other LPC2xxx) to 5V solenoid > > drivers (eg. UDN2981's). Can I pull up the outputs of the LPC to > 5V > > with say 10K, to satisfy the input reqmts of the driver? > > And secondly, I cant find a list anywhere in the datasheets of the > > LPC pins which are 5V tolerant, I notice some are specified as 3.3V > + > > 0.6V but I cant figure out which ones, can anyone help please. > > Michael. |
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Reply by ●March 5, 20042004-03-05
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--- In , "onceinfour" <mmack287@h...> wrote: > I suppose this is for the Philips Apps. > OK all pins except a/d are 5V tolerant. What level (in the high > state) will I get on a pin configured as an output if I have a pullup > to 5V, and what current will it draw. Sorry to harp on, but I need > to know what voltage level I can generate for my peripheral device, > and what size of pull-up I can use. I have two observations for you. 1) If you use a pullup, your output should be configured as open collector or open drain (depending on your nomenclature preference). This is done by writing a '0' to the output data and controlling the output drive (on/off or input/output). 2) The data sheet for the UDN2981 says it is TTL compatible. That means the input switching level is between 0.8 and 2.0 volts, so you don't need a pullup to 5 volts. Does that help? |
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Reply by ●March 6, 20042004-03-06
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wrote: >I have two observations for you. > >1) If you use a pullup, your output should be configured as open >collector or open drain (depending on your nomenclature preference). >This is done by writing a '0' to the output data and controlling the >output drive (on/off or input/output). > >2) The data sheet for the UDN2981 says it is TTL compatible. That >means the input switching level is between 0.8 and 2.0 volts, so you >don't need a pullup to 5 volts. Correct answer redsp .... Hmmm, funny that onceinfour didn't work out that a low-impedance cmos output wouldn't pull-up to +5V with a resistor, unless of course the resistor was ridiculously low :) some further thoughts for onceinfour; Of course when the pin is not outputing a low it becomes an input which are designed to be +5V tolerant. The normal method of making an output appear to be open collector is to set the output port low initially and then simply set/reset the direction register (as redsp pointed out) to make the pin flip from low to high-impedance, thus mimicking an open-collector output. Unlike a true open-collector output, the pin cannot handle breakdown voltages greater than the chip is designed for though. But why use pull-ups and open-collector drives for this application when they are redundant anyway? Peter Jakacki |
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