TCA9517A: Usage and electrical specifications

Hello Truenalia,

For some reason it doesn't seem like the image posted properly.  Can you please try to post it again?

Thanks,
Max

Hello,

user4522287 said:

Hello,

Thank you for your reply.

There was a mistake in the configuration I attached.
I will attach the modified circuit. (I modified the EN connection.)

I assume that EN connects to the output of REG710 just like VCCB.
Even before the Master wakes up, the Slave wakes up.
Is this a problem?

[Bobby] I do see a potential problem since VccA and VccB can both be powered up with EN pulled high but B side pull up resistors may not be present. You could have a situation where B side is floating since the pull up resistor looks like it is supplied by another PCB (pull up named 3.3V_system). You may want to have the EN pin be referenced to GND until it connects to the master PCB.

Please let me know the recommended constant of the pull-down resistor.

[Bobby] You mean pull up resistor correct? This depends on communication speed and expected bus capacitance. We have an app note to calculate this here: http://www.ti.com/lit/slva689

GND is common to the two PCBs.
(Connected to the GND of the Li-ion battery.)

Please answer the following questions as well.

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Also, In my circuit, is VOL less than 0.6V under any condition?

[Bobby] It looks like figure 2 in the datasheet shows VoLB is worse with higher IoL and higher temperature.

The electrical characteristics state if you keep IoL below 6mA, VccB between 2.7V to 5.5V, and temperature between -40C to 85C then the maximum VoLB would be 0.6V though a majority of cases the VoLB would be closer to 0.52V. I think this measurement is a DC measurement though.

(About variations such as differences between LOTs, individual differences, temperature..)

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Best Regards,

user4522287 said:

Hello,

Thank you for your reply.

①[Bobby] I do see a potential problem since VccA and VccB can both be powered up with EN pulled high but B side pull up resistors may not be present. You could have a situation where B side is floating since the pull up resistor looks like it is supplied by another PCB (pull up named 3.3V_system). You may want to have the EN pin be referenced to GND until it connects to the master PCB.

→As you say, the B side may float.
What are the risks if the B side is floating?
I think that there is no problem because I put the initialization process of I2C communication when the master starts up.

 [Bobby] Icc would likely increase due to the input stage of the device floating. This would affect applications which rely on a battery. The second problem is if the input floats low, it could pull SDA/SCL low on the slave side. This could generate a start condition and get the slave's state machine into a stage where it thinks there is an I2C transaction going on. Though the possibility is low, it could also see it's own address and a read/write bit. 

 

②[Bobby] You mean pull up resistor correct? This depends on communication speed and expected bus capacitance. We have an app note to calculate this here: http://www.ti.com/lit/slva689

→I want to know the recommended constant of the pull-down resistor for the EN pin.

 [Bobby] I think the internal pull up on En is in the order of 80k or so (highest being 100k and lowest probably around 60k). You would need the voltage to be less than 30% of VccB to register the enable pin as a low. In the case of 100k, R pull down would need to be 42k or less. In the case of 60k, R pull down needs to be 25k or less. The worst case would be 60k so i would suggest 20k for a pull down.

 

I understand about VOL.
Thank you very much.

 

Comments made below your pink ones in bold.

-Bobby