LPC55S69 GPIO drive strength

[scottm]

In the LPC55S69 manual and data sheet, there are a few references to 'normal drive strength' for GPIO pins. I can't see anything that suggests they have a high drive strength option, and I'm having a hard time finding where it specifies what the actual drive strength is.

Table 24 gives static pin characteristics. It shows +/- 4 mA as the conditions for the Voh and Vol parameters but they're not given as limits. Is there a limit or output impedance given that I'm not seeing? Or do the pins just source and sink 4 mA? And there's no high drive strength option, right? That language is just a holdover from other devices?

Thanks,

Scott

[ZhangJennie]

HI scottm 

Ioh =  + 4 mA is the condition of minimal value of Voh (Vdd-0.5), which can meet most of users high-leval output voltage requirement.

You can set Ioh >4mA, but with this condition, normally the minimal value of Voh could be lower than (Vdd-0.5) due to internal impedance, we don't have other test data for that. you can test the Voh, if the output voltage meets your requirement.

This is the same for Iol. 

Have a nice day,

Jun Zhang

[scottm]

In this case, the pin is an SCT output directly driving an IR LED with a Vf of 1.2 - 1.6 V. At this point I'm just trying to determine if I'm likely to get the brightness out of it that I need or if it's going to need an external transistor. It works adequately on the Coldfire and Kinetis predecessors but those both have high drive strength options for their GPIOs and I'm trying to compare their specs to those of the LPC part.

Scott

[ZhangJennie]

Which Kinetis part do you work with?

Do you use open drain GPIO?

Is there any drive strengh statistic in datasheet?

[scottm]

The previous version used the MK22FN1M0AVLH12, and before that the MCF51JM128. It's been a while since I looked at the datasheets but I'd swear they gave values for pin source/sink currents for both standard and high drive, or at least a graph.

The reference manual for the LPC55SS69 has a couple of references to standard drive strength. There's not a high drive mode for the device though, is there?

At this point I mostly want to make sure I'm not causing damage to the IO pin driver. If it's not prone to damage even in a short circuit then I'll just do some real world testing and see if I get the brightness I need out of the IR LED or if I need to add an external driver.

Scott

[ZhangJennie]

Hi scottm 

NO, LPC55S69 IO pad is not high drive.

Thanks,

Jun Zhang