TXS0108E: Calculation of VOL

u-ted

Prodigy 165 points

Part Number: TXS0108E
Other Parts Discussed in Thread: TXB0104

I'd like to make sure the way to calculate Vol of TXS0108E B port.

For example, it is provided like that VOL = VCCx × 4.5 kΩ / (RPU + 4.5 kΩ) in TXB0104.

What about VOL of TXS0108E? Could you provide equation?

BestRegards.

over 4 years ago

0 u-ted over 4 years ago

Prodigy 165 points

I assume external pull up.

0 Clemens Ladisch over 4 years ago

Guru 287370 points

The TXS has an entirely different architecture. You can compute the resistance of the switch from the V_OL specification (R = (V_OLx − V_ILy) / I_OL), and then compute the voltage drop over the switch with the current through the switch (which is the total current through the internal 40 kΩ resistor and the external resistor). See A Guide to Voltage Translation With TXS-Type Translators

0 Dylan Hubbard over 4 years ago in reply to u-ted

TI__Mastermind 44905 points

Hey U-ted,

Vol for the TXB device is different from the TXS device and I don't think there is an easy equation for it as you would see with the TXB device (its just a voltage divider equation). Vol for the TXS device will vary with the drive strength of the device pulling the input low. You would then have an offset across the pass fet Rdson which will be dependent on the current provided by the pull-ups on the output side.

0 u-ted over 4 years ago in reply to Dylan Hubbard

Prodigy 165 points

Thank you for your reply.

If external pull-up (Rext_pu) is assumed at Bport, can Vol be calculated using following?

Vcc_ext * R/(R + Rext_pu//40K) = Vol

at R = (VOLx − VILy) / IOL

And the following diagram shows architecture of TXS0108E.
Are R1 and R2 not determined? ( Npass would have 300ohm to 500ohm according to datasheet)

BestRegards

0 Clemens Ladisch over 4 years ago in reply to u-ted

Guru 287370 points

The three individual components do not matter; everything is part of the switch resistance: R = R1 + Rpass + R2

The voltage at the output pin is the voltage at the input pin plus the voltage drop over the switch, approximately: V_OB = V_IA + R × (V_CCB / (R_PUB || R_PUext))

0 u-ted over 4 years ago in reply to Clemens Ladisch

Prodigy 165 points

I'm sorry for late reply.
I understand.

BestRegards

Logic

Logic forum

TXS0108E: Calculation of VOL