Well I don't know what all the fuss is about. I never had a problem with one of these.or theseThey both work the same way. The output voltage is determined by the Vcc. (3.3V or 5V). The device is 5V tolerant when running on 3.3V. Therefore, if you THINK about it, you CANNOT use the SAME chip to go BOTH ways.If you have some signals that need to go from 3.3V to 5V, you need one chip dedicated to that purpose. If you have OTHER signals that need to go from 5v to 3.3V you need ANOTHER chip didicated to that purpose. In the case of the OP's application, IF he had purchased the XTB instead of the XTS, he could use the SAME chip because it is BIDIRECTIONAL. I stated that he does NOT have a BIDIRECTIONAL application because he does NOT in point of fact, have a single signal that must go BOTH directions. All of the signals in his circuit are either 3.3V to 5V OR 5V to 3.3V. That makes it a MONODIRECTIONAL application. That being said, there is ,in fact some convenience in being able to accomplish both directions with ONE chip, even if NONE of the signals are going BOTH ways. The XTB should be capable of doing this because it has TWO supply voltage inputs and it is bidirectional so signals can go either way. It is , however NOT necessary , for the reasons given, and offers only the convenience I described in the case of the OP's application. I happen to have the XTB and NOT the XTS but have had issues with insufficient bias current to change the direction of the signal so I rely on something foolproof like the two chips linked above . These have never failed to perform the required function.
Umm, no? If the clamp diode is missing in the simple resistor-diode circuit, then the protection diode performs the same function. The resistor is still there so the full 5V is never presented to the protection diode. Unless the resistor is some stupidly low value then this would never endanger the protection diode. If it is stupid, then I maintain that it would not have worked in the first place.
but the internal diode has no actual spec.
I can't speak for the internal diode in a logic level converter but Atmel recommends not exceeding 1 mA through the ATmega328 internal diodes. I understand that removing power to the chip with voltage on an input pin is the same as doing that with an UNO which causes BACKFEEDING through the internal diodes.
Atmel AVR182, very top of page 4.
The series input resistor is a 1 MΩ resistor. It is not recommended that the clampingdiodes are conducting more than maximum 1 mA and 1 MΩ will then allow a maximumvoltage of approximately 1,000V.
reread the Atmel AVR182/page-4 comment. It mentions a 1 Mohm resistor.