TS3A5223: Can the device be used to switch I2C SDA/SCL signal ?

Kawai,

TS3A5223 can be used for I2C signals. However, as you noticed NC/NO/COM pins are limited to Vcc.

To support the case where 3.3V signals are applied to the NC/NO/COM pins with Vcc=0V, a device with "powered-off protection" feature is required.

TMUX136 device is an alternate that supports the power-off protection feature and also has the benifit of very low ON-Capacitance which will minimize capacitive bus loading on I2C lines.

For reference, here is a link to an application note related to power-off protection. http://www.ti.com/lit/pdf/scda01

Kawai,

Q1) Yes, since I2C is only a 5V <1MHz protocol almost every switch at TI will support I2C signals.  We have highlighted a quick search button to pick some popular configurations (basically all 2 channel switches) since we get so many questions on the forum about I2C signals. 

Q2) No, operating the device under abs max ratings may cause permanent damage as stated in note 1 of the abs max table.  You will need to select a device that has powered off protection and will state a max voltage in the recommended operating conditions to ensure there might not be damage.

What do you think about using the TS5A23160 or TS5A23159 device instead? You can see that this device will remain high impedance when V+ = 0V event if 5V is placed on one of the I/O pins.

Q3) As stated in Q2 operating the device with VNC/VNO/VCOM may cause permanent damage to the IC.

Thank you,

Adam

Kawai,

Q4). How can we know if the switch supports "Power-off Protection" ?

The ti.com switch selection tool has filters that can narrow down devices that are 2:1 configuration, have powered off protection feature, supports I2C signals, and Vdd min <1.8V. 

In the TS5A23159 datasheet you can see the leakage specification on the COM and NO/NC pins when Vcc = 0V.  This ensures that there will be a high impedance path from COM to NO/NC when Vcc = 0V.  This spec is only valid when Vcc =0V.  When Vcc is at any other value the absolute maximum rating spec of Vcc + 0.5V on the COM and NO pins comes into play.   

Q5). Below are the absolute maximum ratings which is listed in the datasheet for each devices. My understanding is that TS5A23159/23160 cannot be used in this case since Absolute Maximum Ratings (AMR) is "VCC+0.5V". I believe these devices will be damaged if signal applied without VCC power supplied. Why can you recommend these devices ?

Please see the answer to Q4.  The powered off protection is only valid when Vcc = 0V.  If the Vcc node is floating it is possible that Vcc will not be 0V and the abs max rating must be observed. 

Q6). TS3A5223 AMR for VCOM/VNO/VNC are 4.3V maximum. Recommended operating conditions for these pins are VCC. If I2C communication can be ignored when TS3A5223 VCC is not applied can they use the device ? Or, does the device get damaged even used under AMR ?

If you have Vcc =0V and the I2C communication is not present you can use any device in the portfolio. The TS3A5223 will operate with Vcc = 1.8V.

Q7). TMUX136 seems to meet the requirement of applying signal without VCC power supply. However, customer wants to use at VCC = 1.8V. Do you have alternative solution ?

If you can ensure Vcc = 0V during the powered off condition than the TS5A23159 or TS5A23160 would be good choices. 

Take a look at the new TMUX1511 device.  Its not the ideal configuration but has the specs I think you want.  You could tie out puts of the D1/D2 and D3/D4 to create effectively a 2-channel 2:1 device. 

Thank you,

Adam

Kawai,

Q8). Let's say the switch device is not power supplied yet, however,  "NC"  pin has 1.8V applied through pull up resistor which I2C bus connected from the other board.In this case, can the switch device stand for this continuous 1.8V voltage ?

TS3A5223 doesn't have any powered off protection feature and clearly states recommended operating condition on NC pins as Vcc max.  If you are concerned about this operating condition this would not be the device to choose

TS5A23159 has powered off protection and will remain Hi-Z when Vcc = 0V.

TMUX1072 recommended operating conditions for the signal path is not restricted to be within Vcc since this device as beyond Vcc feature.

Q9) What happens when the switch device is powered up (VCC supplied) at the above condition ? There is a state when VCC is not 0V, however, analog voltage is applied to NC pin. Is this exceeding the AMR ?

NC = 1.8V
VCC = 0V -> 1.8V 

What happens in this condition is undefined since it is outside the recommended operating conditions.  The TS3A5223 cannot guarantee Hi-Z signal path until Vcc is valid.

Q10) If VCC is directly connected to DC/DC converter, can you say Powered Off Protection is available ?
My guess is that this is similar to having VCC pin floating.

I don't think you can say Vcc = 0V since the node could be floating.  You can add a weak pull down on the node if there is a concern in your system.

Thank you,

Adam

Kawai,

Please see note 4 of the absolute maximum ratings.

When voltage on the signal path is greater than Vcc the ESD protection circuity can turn on and leak current to Vcc.  This is why the datasheet doesn't recommend this operation and can't guarantee the electrical characteristics stated in the datasheet.

In an I2C application the series DC resistance is negligible because the pull up resistors will be in the 1000s of ohms any way.  The nice feature about the TMUX1072 is the beyond Vcc operation that it can support the recommended operating condition of the signal voltage being greater than Vcc.

Thank you,

Adam