VOH/VOL worst case

[Jeff]

A couple questions about the nRF52840 GPIO Electrical Specification:

1. In the nRF52840 GPIO Electrical specification, VOH at 0.5mA is spec'd to go as low as VDD - 0.4V, and up to VSS + 0.4V.

If the device is connected to another digital input, the current will be much less than this, such as <10uA.  Is it possible to specity the VOH(min) and VOL(max) at a low current with tighter specifications, ideally VOH(min) = 0.95*VDD, VOL(max) = 0.05*VDD, etc?

2. VIH(max) is specified as VDD.  In other parts this typically has a margin, such as VDD+0.3, to allow for supply variation.  Are you able to provide some margin to VIH(max)?

For example if the nRF52840 has its own VDD set to 1.8V, but is actually 1.7V due to the internal DCDC regulator inaccuracy, and is communicating with something that has a different 1.8V supply that is actually 1.85V due to regulator accuracy, an IO driven by the other device might get to 1.85V (0.15V above the nRF52840's VDD).

Thanks,

Jeff

[haakonsh]

1. The VDD - 0.4V and VSS + 0.4V specs are extremely conservative.
   The 52840 is similar to the 52832's gpio spec:  GPIO Electrical Specification:
   
   From Figure 3, you'll see that a source current of 0.5mA will yield a voltage drop of ~0.1V, which is far less than the spec's 0.4V.
   A source current of <10µA will yield a much lower voltage drop than that again, you can also reduce the voltage drop further by using high drive strength instead of normal. See Figure 4.
   
   Figure 3 and 4 are simulated worst-case scenarios btw, the reality will be somewhat different. 
   
   
2. From Absolute maximum ratings: VDD + 0.3 V or 3.9V if VDD > 3.6V. 

 

[Jeff]

Thanks!