BQ28550 No smbus communication

Make sure jumpers J3 and J4 are shunted.

Thanks for your response. I connected EV2300 smbus port to SDA and SCL of my board (I don't have EVM board), and found out 3V at SCL and 1.9V at SDA. Do I need to add extra pull up 3.3K resistors for them, together with EV2300? For smbus communication, do I need to pull up the pin12 with a 3.3K resistor, like datasheet suggested?

The user's guide has a typo. J3 and J4 should be shunted. J2 should not be shunted.

Thanks a lot.

I was told that the bq28550 smbus communicate normally after pull up the pin12, by my colleague who is at UK. It looks like the information I got is incorrect.

Pin 12 is the HDQ line. It doesn't have any function in this particular device, however.

That's also my understanding (pin12 is for HDQ). But I colleague told me, without pull up pin12, the smbus won't build up the communication with EV2300. It looks like to pull up pin12 matches the diagram in datasheet page 3 (Figure2. Block Diagram). My colleague said that he found out the pin12 is a selection pin for smbus or HOQ from a TI doc, but he can't remember which one it is.

Your colleague may be thinking of a different device. There are some other handheld gauges that do communicate HDQ and they may have some sort of selection pin. The bq28550 does not utilize pin 12 at all, though. So leaving it floating or pulling it up will have no effect on the operation of the gauge.

Should J6 still be shunted? Are the transistors Q3-A/B needed for SMBus communication? Or can they be left out of this application as well? Can pin 12 really be left open?

Brenton,

Kindly indicate what schematic you are refering to.

thanks

Onyx

Thank you for the reply Onyx. We tried the 6 bit addressing in the format you recommended, but are still not seeing the slave pull the data line low in Acknowledgement of the address. The schematic I was referring to is the REFERENCE SCHEMATIC on page 33 of the bq28550-R1 datasheet. This schematic shows pin 12 (HDQ) connected through J6 to Q3 and R15, R16 and R17. Because we were not using HDQ in our application, we have left all of these components out of our circuit and left pin 12 open. Could this be causing the I2C problems?