SN74CB3Q16211: Ron resistance measurement

Page 4 of datasheet mentioned the absolute maximal ON state current is +-64mA. This 40mA is under the absolute maximal ON state current, There is no recommended maximal current shown at the datasheet.  Can you tell me what is the maximal allowed I/O port current for this CB3Q device?

The maximum allowed current is 64 mA.

The maximum current for which the maximum resistance is specified is 30 mA.

Will the ON state resistance increase as port current increase? If yes, do you have the related chart? Datasheet only shows the relationship between Vin and ON state resistance.

We have already tried 220ohm and 150ohm.  The following were the measurement:

150ohms:   current = 28mA,  Ron = 28 ohms

220ohms    current = 18.6mA,  Ron = 48ohms.

Looks like the higher the channel current, the lower the Ron is.  But the measured Ron values are still way off from the 5ohm in the spec.

These values are unlikely to be correct; MOSFETs sature at higher currents.

How accurate is the 5 V supply? How did you measure the current? Can't you measure the resistance (or voltage drop) directly with a multimeter?

Hi Jack, Daniel,

The datasheet RON parameter was characterized using a current of 15/30mA and specified input voltages of 1.7V and 2.4V at VCC = 2.3, 2.5, and 3V (so essentially the conditions in your setup are not identical, so there will be deviations from the datasheet values). Normally, when there is an increase in current, this would lead to the device heating up and an increase in the on-resistance. In addition, the higher the input voltage is relative to the supply, this also causes an increase in resistance as well (you can see this in figure 1 of the datasheet). Given that your application is using a higher current and higher input voltage, I would expect there to be a higher resistance seen from the device itself due to self heating and behavior of the multiplexer architecture at these voltage nodes.

Now, with all that said, 25ohms/48ohms seem to be pretty high regardless so I am curious if you can share the schematic of the circuit you are using the multiplexer in. In addition, have you take the device off the board and tried to just evaluate the multiplexer on its own with those input conditions and see if you get the same results?

Thanks!

Bryan

5V supply is verified by both the digital display on the power supply unit and a multimeter.  I have measured the current with two different ways (1) a multimeter in series connection to read the current level directly (2) voltage drop across the 150/220ohms resistor.    

Hi Bryan,  I have already tried taking the measurement at the levels closer to the ones in the spec but still got high channel resistance.  We ordered the device from Mouser and I took the measurement directly from the device without using a board. (just some hanging wires soldered to the tiny pins). Our intent is to use the switch to control the supply of a test design, so the voltage drop along the channel cannot be too large.   I will confirm all my testing again using levels defined in the spec and updated the finding soon with the schematic.  Thanks

Hi Jack,

Thanks for providing these details and let me know if you can confirm your findings. Schematic will be super useful as well.

Let me know once you have these additional items and we can further investigate.

Thanks!

Bryan

Hi Jack,

Great news! Glad we were able to resolve this.

Let me know if there is anything else!

Thanks!

Bryan