nRF51 -- max. I/O pad diode current to avoid latchup?

[ScottBBBB]

We have identified a possible transient fault condition in which a voltage in excess of VDD can be applied to an I/O of the nRF51. VDD is 3 V and the excess voltage would be nominally 5 V. We will include a series resistor to limit current, but we're limited in how large this can be. Some ICs provide a spec for the max. current which can flow through the pad diode from I/O line to VDD before latchup could occur, but I don't see such a spec published for the nRF51. Is this value known?

Thanks, Scott

[bjorn-spockeli]

Hi Scott,

the nRF51822 can source/sink GPIO pins with maximum 15mA totally. This means that you should not let combined sink and source current of all GPIOs exceed 15mA at any time. Its not stated specifically, but its stated that the maximum current the nRF51x22 can source is 15mA ( 3 pins configured as high drive) in the nRF51822 Product Specification under Section 8.23(Footnote under table 62).

Best regards

Bjørn

[ScottBBBB]

Hi Bjorn, I don't think we're talking about the same thing. I'm not talking about current flowing through the drive FETs of the GPIO. I'm talking about current which flows when the IO signal is pulled to a level well above VDD. In other words, an abnormal condition, and current won't flow through the FETs but instead through the normally reversed-biased protection diodes in the IO pad. Regards, Scott

[bjorn-spockeli]

Hi Scott, I apologize for the misunderstanding. I am afraid that this value has not been specified and the HW designer I talked to could not provide any maximum value.

[ScottBBBB]

Okay, thank you for confirming. Scott