TCA9617B: Design question

Hi Anne,

We will get back to you tomorrow on this.

Max

Hi Anne,

1. Is there any concern for Enable pin design in the period when VCCA is on but VCCB is not on? 
During power-up the device drivers will remain in an off state until both VccA and VccB have come up above a defined threshold. Once these supply levels are met, the device will become active depending on the state of the enable pin. This is outlined in Section 8.1 paragraph 5. 

2. If we change the VCCA= P3V3_AUX and VCCB=P3V3_Edge, then the channel will be on in the beginning before VCCA= P3V3_AUX on, is there any concern for this design?
See above, the device will only become active once both supplies are above the defined thresholds. 

3. Do we have any suggestion or limitation about the VCCA & VCCB power on sequence?
Be sure that once the threshold for each supply is reached, the supply does not drop below the threshold during the power-up sequence. This could cause the device to become active before the supply is stable. I constant ramp up should avoid this situation. 

4. If we design two TCA9617B B side connect to each other, is it acceptable? 
A configuration where two B-sides are connected together is NOT supported by this device. Because of the static-voltage-offset used on this side of the device, it cannot be connected to any port that uses a similar offset. Please refer to Section 9 on Application and Implementation for more information and examples of acceptable layouts.

Regards,
Eric 

Hi Eric,

Thanks for your feedback,

If we keep the original design as below, and VccA power up earlier than VccB and EN has internal pull up to VccB, is there any current leakage to SCL/SDA to make them be pulled down or any other concern?

Please help to advice.

Thank you 

Hi Anne, 

The snippet you shared is from the TCA9617A datasheet. This device behaves differently than TCA9617B in a power-up state. In the schematic shared above, TCA9617B will keep the outputs SDAx and SCLx in a high impedance state until both supply lines are brought up to a certain voltage.

The datasheet states: "The TCA9617B includes a power-up circuit that keeps the output drivers turned off until VCCB is above 2.0 V and VCCA is above 0.7 V. VCCA is only used to provide references for the A-side input comparators and the powergood-detect circuit. The TCA9617B internal circuitry and all I/Os are powered by the VCCB pin."

Let me know if this answers your question.

Regards,
Eric

Hi Eric,

Appreciate for your explanation from the mentioned below, the power sequence on our board would be VCCA power up earlier than VCCB which still violates with spec this sentence “until VCCB is above 2.0 V and VCCA is above 0.7 V”.

Just wonder what would be happening about this violation?

Thanks

"The TCA9617B includes a power-up circuit that keeps the output drivers turned off until VCCB is above 2.0 V and VCCA is above 0.7 V.

VCCA is only used to provide references for the A-side input comparators and the power good-detect circuit. The TCA9617B internal circuitry and all I/Os are powered by the VCCB pin."

Hi Anne,

I believe this section of text indicates that the device ports will remain in a high impedance mode until both supplies are active. In the case where VccA is provided while VccB remains inactive, the device will remain in this high-Z state. Once VccB rises above its threshold with VccA already supplied, the device will begin to function normally.

Let me know if I've understood your question correctly.

Regards,
Eric

Hi Anne,

Were you able to confirm your design using the information above?

Regards,
Eric