TCA9545A: RON

Ting Zeng

Part Number: TCA9545A

Hi there

I have some questions about TCA9545A

1.May I ask how to measure the RON,follow is the answer on your E2E forum，Is it like this？can you show me a diagram？

[Bobby] I imagine you may need to place a small resistor before the SDA/SCL and after SDn/SCn and adjust the resistance such that you pull 15mA/10mA while the Vo (seen by the SDn/SCn is 0.4V while SDA/SCL is tied to Vcc through that small resistor). Then you would take the voltage drop across the channel and divide by 15mA/10mA.

2.If sda input low level VIn is 200MV ，VOL = pass gate dropout +200MV , Is It right？

3. Is the pass-gate ON when transfer low level only，off when transfer high level？

over 2 years ago

0 Tyler Townsend over 2 years ago

TI__Mastermind 23943 points

Hi Ting,

Let me get back with you tomorrow by around 3pm CST tomorrow.

Regards,

Tyler

0 Tyler Townsend over 2 years ago

TI__Mastermind 23943 points

Hi Ting,

(1) For measuring Ron, I would recommend a similar test setup.

Adjust the pullup resistor Rp to limit current to datasheet spec of 10mA/15mA of current through the internal passFET while driving the SDN side low. Measure V1 to be about the same as Vo = 0.4V, since technically if you drive the SDN side low, V1 = Vo.

Ron = (V1 - V2) / (10mA or 15mA)

(2) Your logic makes sense here. Vol = Rds_on * Iol + 200mV.

(3) Yes. The internal pass-gate is only ON when either side of the bus pulls low to GND. When I2C is in its recessive state pulled HIGH to VCC, the internal FET is biased off.

Regards,

Tyler

0 Ting Zeng over 2 years ago in reply to Tyler Townsend

Prodigy 20 points

Hi Tyler,

for the first question,the Ron is 7-45@vcc=2.3-2.7 and 10-70@vcc=1.65-1.95 when Io=10mA,Vo=0.4V.

then,Ron *Io=70*10mA>0.4;VIN=Vo-Ron*Io,Vin may be negtive voltage?

0 Eric Schott1 over 2 years ago in reply to Ting Zeng

TI__Mastermind 48215 points

Hi Ting,

This is a bidirectional device, so it's possible to measure the Ron characteristic in either direction. The range given for these specifications is across the operational range of the device, including supply voltages, temperature, current ranges, etc. Not all of the maximum or minimum specifications occur at the same extreme, so you may get conflicting results when only using worst-case values here.

Regards,
Eric Schott

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TCA9545A: RON