PCA9544A: VOL characteristic value of PCA9544A

Conor

Part Number: PCA9544A
Other Parts Discussed in Thread: TCA9800, TCA9544A, TCA9617A, TCA9617B

Hi,

In the data sheet, the condition for VOL = 0.4V is IOL = 3mA, but do you have any data on the VOL characteristic value under the condition of 3mA or less?

In the current circuit configuration, VIL on the opposite side is 0.36V. We believe that if the IOL current value decreases, the VOL voltage value will decrease accordingly.

Thanks,

Conor

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 287020 points

0.4 V at 3 mA or 0.6 V at 6 mA are the two limits required by the I²C specification.

Please note that the PCA9544A is a passive switch; these specifications do not apply to I²C accesses to any devices on the four slave channels.

0.36 V does not conform to the I²C specification. Which device is this? Can you show a schematic? It might be necessary to add I²C buffers like the TCA9800.

0 Eric Hackett over 1 year ago in reply to Clemens Ladisch

TI__Guru 72272 points

Thanks for the help Clemens!

Conor,

Thanks for bringing this to E2E, and your continued patience. Because of US national holiday, several of our TI experts are out, but will get back to you by end of business on 07/05/2023 CST.

Regards,

Eric Hackett

0 Conor over 1 year ago in reply to Clemens Ladisch

Guru 10180 points

Hi Clemens Eric,

Clemens Ladisch said:
Which device is this? Can you show a schematic?

I will attach a simple connection configuration. The counterpart device is MicroChip's EEPROM, which converts 2.5V-1.8V via FETBus-SW.

Thanks,

Conor

0 Clemens Ladisch over 1 year ago in reply to Conor

Guru 287020 points

Please note that all three pull-up resistors (R1, R2, and the one on the other side of the switch) act in parallel. To reduce the V_OL, use higher resistor values so that the total pull-up current is much less than 3 mA. (If your bus is so large that it has a very high capacitance, this might require reducing the frequency.)

If you use the TCA9544A instead, you can run it at 1.8 V to allow level shifting from/to 1.8 V. (The internal switches are MOSFETs just like U1.) This would remove the need for the discrete level shifter and the third pullup.

0 Conor over 1 year ago in reply to Clemens Ladisch

Guru 10180 points

Hi,

I have a question about the TCA9544A.

Q1
Am I correct in my understanding that the VCCA margin is allowed up to VCCB +0.5V? Also, is it correct to assume that the TCA9544B is the same?

Q2
Are there any restrictions on the power sequence of VCCA and VCCB?

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/868848/tca9617a-power-sequence-question?tisearch=e2e-sitesearch&keymatch=TCA9617A

Thnaks,

0 Clemens Ladisch over 1 year ago in reply to Conor

Guru 287020 points

Your questions do not apply to the TCA9544A. Assuming that you mean the TCA9617A:

1. The datasheet does not mention 0.5 V. But assuming that there is a diode between the supplies, then 0.5 V sounds OK.

2. Section 10 of the respective datasheets answer this. The TCA9617A requires V_CCB to be powered not after V_CCA; the TCA9617B does not have this restriction.

0 Tyler Townsend over 1 year ago in reply to Conor

TI__Mastermind 33753 points

Hi Conor,

Please let me know if you have any more questions.

Regards,

Tyler

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PCA9544A: VOL characteristic value of PCA9544A