Hello everyone,
I've been reading the TXS0108E datasheets and I've come across a confusing bit of information. Apparently (in Section 6.5 of the datasheet), the typical output voltage is 0.67*Vcci (where Vcci is the supply for the relevant section). This would mean that if you were using the TXS0108E in a 3.3V to 5V level conversion application, it would actually be converting 3.3V to 3.35V (5V * 0.67 = 3.35V). This doesn't seem like a very useful thing to do.
It would also mean that you couldn't use a TXS0108E to convert 5V or 1.8V to 3.3V for use by an MSP430C1101 (that was the first MSP430 I looked at) because the Vih threshold on the MSP430 is 0.8*Vcc (2.64V) and the TXS0108E would only output 0.67*Vcc (2.21V).
Is this a mistake in the datasheet?
A bit about my application: I need to have a bunch of bidirectional pins that can accept signals that could be "high" anywhere between 3V and 5V, and also output signals at 5V. I need to be able to achieve 10Mbps or so, but there can only be very weak pull-up resistors (over 10K) on the outputs. The other side of the level conversion will be 3.3V, with a microcontroller attached.
The open-drain translators (eg. LSF0108) won't work because for high speed they need strong pull-ups. The TXS and TXB series thresholds are unfortunately too high to accept a 3V input when operating from 5V, and (as above) the TXS won't provide a 5V output when operating from 5V.
Currently the plan is to use one SN74LV1T126 chip per pin, powered from 5V. When in output mode it'll just act as a normal 3.3V to 5V level translator. When in input mode it'll be disabled, and the signal will be routed to a 5V-tolerant pin on a 3.3V microcontroller (which has a threshold low enough to handle a 3V signal). This is a mess (lots of chips, extra resistors, two pins on the microcontroller per chip in order to provide both data and enable) but I can't see any better option. A bidirectional level converter or a 5V MCU would work nicely, but only if it would accept 3V signals - and so far I can't find any.
Any help - either with the TXS0108E datasheet or the more general level conversion problem - would be much appreciated.
