DS90UB949-Q1: I2C address settings of FPD-Link III serializer-deserializers DS90UB925Q/DS90UB926Q, DS90UB948-Q1

Hello,

Please help me to double-check the resistor values related to the I2C settings of number of TI serializer-deserializers.

In our company we are using extensively FPD-Link III serializer-deserializer pairs such as DS90UB948-Q1 - DS90UB949-Q1 and DS90UB925Q - DS90UB926Q. Respectively we have number of carry-over blocks shared between projects. Related, one of the issues we face are the required diverse resistors for setting the I2C addresses. Those diverse values pose challenge to our production of course. For example, a schematic update from the deserializer DS90UB926Q to the deserializer DS90UB926Q-Q1 requires different I2C setting resistors. Surprisingly those two devices have entirely different tables for setting the I2C addresses. For setting an I2C address 0x2D, for the first device the required divider R1/R2 is 292k/40.2k, while the second one required divider is 124k/17.4k. Respectively, if the pairing serializer is DS90UB926Q-Q1, its required resistors match the resistor settings for DS90UB926Q. Further, regarding the Bridge Deserializer DS90UB949-Q1, for using the second I2C address in its table the required R1/R2 divider is 118k/30.9k.

To get around the precise diverse values we try to stick to single pull-up or pull-down resistors whenever possible. Thus, we stick to the First and Last values in the I2C address tables whenever this is beneficial. Even taking such approach, the current situation is shown below:

Table of First, Second and Last I2C addresses,
Required Pul-Up/Pull-Down resistors in kOhms:

Device,                       First I2C addr,            Second I2C addr,        Last I2C addr

DS90UB925Q,         40.2 PD or any,        294/40.2,                    90.9/243
DS90UH925Q,         40.2 PD or any,        294/40.2,                    90.9/243
DS90UH925Q-Q1,   40.2 PD or any,        294/40.2,                    90.9/243
DS90UB926Q,         40.2 PD or any,        294/40.2,                    90.9/243
DS90UB926Q-Q1,   40.2 PD,                    124/17.4,                    57.6/121
DS90UB948-Q1,      40.2 PD or >10,        232/47.5,                    45.3/182
DS90UB949-Q1,      40.2 PD,                    118/30.9,                    13.3 pull-up

Now the question:

In our projects, for setting the FPD-Link Id, whenever a single PU or a single PD is required we use the value of 10k.
Do you think such choice leads to any possible violation or design risk?
In the case of DS90UB949-Q1 the required Pull-Up resistor is very particular: 13.3k. Is that particular value important or we can use any resistor? In the case of DS90UB948-Q1 the requirement for the pull-down resistor is ‘’> 10”. Is that mean that 10k is not recommended for any particular reason?

Thank you,

~~~~~~~~~~~~~~~~~ 
Zavarin Gagov
Hardware Engineer
~~~~~~~~~~~~~~~~~ 
Skyships Automotive Limited
Leighs Lodge, Willows Green, Chelmsford, Essex, CM3 1QJ, UK
office:   +44 (0)1245 362980,  mobile: +44 (0)7549 992515