Part Number: TS3A24159
Hello to TI support team ,
I want use TS31A24159 SPDT as multiplexer for SMBus protocol signals , Can you recommend if this IC fits this mission ? I see high capacitance ( ~200pF) COM , NC , NO to GND , this is the reason i want consult .
Hey Alexander,Was there a reasoning for picking the TS31A24159? I mean to ask to see if there was a specific spec you were most interest in when you picked this part. I see that of the 2 channel SPDT switches it has the lowest On-Resistance. This typically isn't as important as the On-Capacitance for digital applications such as SMBus protocol. So we'd probably want a 2 channel, SPDT with Low Con.The TI.com search tool can help. Here i've shown an example where I filtered out 2 channel SPDT like the TS31A24159 and added a filter for features being supporting I2C signals. I2C and SMBus are fairly similar signals so anything we find should be applicable. Additionally, i've added On-Capacitance on the list of features listed and sorted from lowest to highest C-on. You can see all the options we have and even add '1.8V compatible' to the features to be sorted through, as it looks that the TS3A24159 is 1.8 logic compatible. Here's the final list of devices that would be work. The TMUX136 or TMUX154E would both be good options.Hope this helps,Rami Mooti
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In reply to Rami Mooti1:
Hi Rami ,
Thanks alot for your quick answear ,
1. Was there a reasoning for picking the TS31A24159? --> it suits the description on ti site fits I2C protocol .
2. I have re-design now and need to locate 2 units series connected SPDT between uC and smart battery, as i understand two series connected TS31A24159 make exceed capacitance on both lines > 400pF according to I2C/SMBus spec and it make do problem in transition from '0' to '1' due to `high or excessive R (pull up ) X C (parasitic capacitance, include capacitance of SPDT NO, NC to ground each one ~220pF X2 )
3.Is it availabe pin to pin IC bi directional SPDT for I2C/SMBus to solve described problem on par.2 .
In reply to Alexander Burtakov:
Alex,So yes this would be a problem, as you said, per I2C standards 400pF is the max limit and two of these chips in series would cause a problem when the switches are turned on as the capacitance would accumulate. If you're wanting two in series I would look for a SPDT who's C-on is much lower.The TMUX136/TMUX154E won't be pin to pin but just to get a feel of what we're working with here, are we hard set on keeping the the TS3A24159 footprint in place? As in can this not be replaced? If so can you give me an idea or a block diagram of what you're trying to accomplish so I can better understand the problem?If i'm grasping this problem properly though, we either can't remove or we would prefer not to move the first TS3A24159 but still require to have two SPDT switches in series but (rightfully) worry about the capacitance being too high. An idea would be to use the TS3A24159 (with ~250pF) then one of the TMUX136 (~1.5pF) and you could really minimize the capacitant load Let me know what you think,Rami Mooti
Hello Rami ,
1. so can you give me an idea or a block diagram of what you're trying to accomplish so I can better understand the problem? ---> Attach figure of my scheme .
4 modes operation :
1. Battery #1 communicate with uc #1 and bat #2 disconnected .
2.Battery #2 communicate with uc #1 and bat #2 disconnected . (U13 SET)
3 Battery #1 communicate with uc #2 and bat #2 disconnected (U12 SET)
4.Battery #2 communicate with uc #2 and bat #1 disconnected (U12,U14 SET)
Thanks , Alex Burtakov . .
Alex,So i'm seeing if you're trying to pass an I2C signal from uC #1 or #2 through U12 then through U13 to either of the smart batteries you're going to accumulate more capacitance than is typically allowed per typical I2C usage. You're going to see nearly 500pF by cascading these devices.If you're hard set on using the TS3A24159DGS, I would think you're going to run into communication errors. As mentioned before, I would recommend using a chip with lower On Capacitance. You can sort this out from lowest C-on to highest on the TI.com search tool.The TMUX1072 is another good choice that comes in the same DGS package you're working with the TS3A24259. TMUX1072 also supports signals past the Vcc supply rail, that is to say at only 3.3V at the supply you can still support 5V I2C.Rami
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