STM6905 RST output

[aleblancnuv]

The STM6905 datasheet says in Table 2 that there is an internal 10k pull-up on RST#, which seems wrong since that's an open-drain output. Then in Section 2.6 and in Section 3 it says that an external pull-up to VCC should be used.

[Peter BENSCH · Accepted solution]

Welcome @aleblancnuv, to the community!

The STM6905 was launched in 2007. The data sheet was last updated in 2014 – but nobody had actually spotted the typo until now! Thank you for your keen observation and for bringing this to our attention!

But to summarise once again: there is a pull-up resistor only on the /MR input, but not on the /RST open-drain output.

Regards
/Peter

[aleblancnuv]

@Peter BENSCH, can the /RST pin have a pull-up to supply that's present while the VCC the device is unpowered? Typically that's OK for open-drain outputs, but the datasheet shows a max input/output voltage of -0.3 to VCC+0.3, which is odd. 

[Peter BENSCH]

No, with a few exceptions, that is entirely typical for integrated devices. In the implementation of the internal function using semiconductors, parasitic pn junctions also arise. Under normal operating conditions, these are reverse-biased; however, if the operating voltage is exceeded or falls below the required level, they act like ordinary diodes. For this reason, going above or below this level must be limited (here 300mV) in order to remain below the forward voltage.

Regards
/Peter