I am using I2C port of FX3 controller to talk to led driver chip. The LED driver chip has registers that can be accessed through I2C bus. FX3 chip is the master device. In the partial drawing below. SCL_M and SDA_M are I2C signal from FX3 controller and are pulled up to 3.3V through 1k resistors at the controller side. SCL and SDA are I2C from led driver chip. When I install R19 and R15 only, FX3 has no problem to access registers of LED driver chip. But when I removed R19 and R15, install U8(LTC4301), R22, R23 and C17 only, FX3 controller can't access registers of LED driver chip anymore. Please let me know what could it be the reason.
Thank you very much. I am in the middle of debugging the prototype board.
The SCLIN and SDAIN pins also need pull ups. They are not in the schematic.
Thank you for reply. SCLIN AND SDAIN are pulled up by 1k resistors.
With a 3.3V pull-up supply for SDAIN and SCLIN you should try the LTC4301 rather than the LTC4301L. The LTC4301L has levels for lower voltages.
Can you get a pull-up and probe on the READY pin to see what state its in? The READY pin should be high if the buffer is ready to start doing its thing.
The ready is low. The data sheet is not clear regarding the signal level. But, I will order LTC4301 and try. Thank you for the help.
If READY is low (and it has a pull-up in place), that saying a step in the start-up sequence is missing. Maybe try to work through the Start-Up section of the datasheet and see if one of those conditions is not being met.
READY pin needs to be pulled up since it is open drain and is pulled down internally. Thus, I pulled up the READY pin. Now the pin level is high which means it complete start-up. But it still does not work. When I2C command sent, signal shows on SCLIN but SCL out is still high. So are SDAIN and SCLOUT.