Logic Level Conversion using TXS0108E
- Thread starter JimKazmer
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BriComp
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After further searching I found this GitHub entry where someone has successfully used the 8 way device and has published a Kikad PCB design for it. Since you only want 4 ways, you could modify the design by moving the chip and the caps up, then just chop off the lower connections which you do not need. This would give a fairly compact footprint close to those of the TSB0104.
I have also since found another 4 channel device of the same family, the LSF0204, but the pinout is different to the LSF010x devices.
I have also since found another 4 channel device of the same family, the LSF0204, but the pinout is different to the LSF010x devices.
BriComp
Well-known member
Bear in mind that they are NOT bi-directional, on this chip one out and one back.
That is ideal for what I want for Serial UART.
I have seen circuitry where one chip provides bi-directional data by connecting the input/output on each side together.
There are many more chips in the family with, from what I can see, up to 6 channels per side arranged in various combinations of out and back direction.
See here.
In the time since my previous posts, I decided to keep using the larger TXS0108 parts (which worked for both SPI and UART). I am now creating PCBs for my electronics instead of generic breadboards, and really want to use a smaller part...
As I re-read the above thread I noticed some of the posts above reference incorrect part numbers like "TSB010#" or "TSX010#"; the correct parts are "TXB010#" and "TXS010#". The "B" is a reference to "buffer" circuitry, and the "S" is a reference to "switch" circuitry.
I am now reading these TI documents:
https://www.ti.com/lit/an/scea043/scea043.pdf (A Guide to Voltage Translation With TXB-Type Translators).
https://www.ti.com/lit/an/scea054a/scea054a.pdf (Effects of External Pullup and Pulldown Resistors on TXS and TXB Devices)
This document was helpful: https://www.ti.com/lit/sg/slyy165a/slyy165a.pdf (Voltage Translation Buying Guide).
The "Effects of External Pullup and Pulldown Resistors on TXS and TXB Devices" was a worthwhile read... there are some referential mistakes in the document that will cause people some confusion or mistakes if you don't catch them. The most useful information contained are the following parts:
The TXS family of translators incorporates internal pullup resistors designed to hold the output when
driving logic high. The internal pullup resistor is fixed at 10 kΩ for the TXS0101, TXS0102, and TXS0104E
translators, whereas the TXS0108E translator has dynamic pullup resistors that change value depending
on whether the output is driving a high or low. When driving a high, the pullup resistor value is 4 kΩ and
when driving a low, the pullup resistor value is 40 kΩ.
The document then gives examples of what different sized pull-ups/pull-downs will do to the output voltage, but uses the TXS0108E as the reference example (which is behaves differently than the other three chips).
Summary: pull-ups okay for TXS010#, but pull-downs less than 50k-ohms very problematic.
The TXB010# includes an internal 4 k-ohm buffer for all parts.
Summary: Pullup and pulldown resistors of less than 50 kΩ must not be used with TXB translators because the internal 4-kΩ buffer and external resistors create a resistor divider network.
more to come...
As I re-read the above thread I noticed some of the posts above reference incorrect part numbers like "TSB010#" or "TSX010#"; the correct parts are "TXB010#" and "TXS010#". The "B" is a reference to "buffer" circuitry, and the "S" is a reference to "switch" circuitry.
I am now reading these TI documents:
https://www.ti.com/lit/an/scea043/scea043.pdf (A Guide to Voltage Translation With TXB-Type Translators).
https://www.ti.com/lit/an/scea054a/scea054a.pdf (Effects of External Pullup and Pulldown Resistors on TXS and TXB Devices)
This document was helpful: https://www.ti.com/lit/sg/slyy165a/slyy165a.pdf (Voltage Translation Buying Guide).
The "Effects of External Pullup and Pulldown Resistors on TXS and TXB Devices" was a worthwhile read... there are some referential mistakes in the document that will cause people some confusion or mistakes if you don't catch them. The most useful information contained are the following parts:
The TXS family of translators incorporates internal pullup resistors designed to hold the output when
driving logic high. The internal pullup resistor is fixed at 10 kΩ for the TXS0101, TXS0102, and TXS0104E
translators, whereas the TXS0108E translator has dynamic pullup resistors that change value depending
on whether the output is driving a high or low. When driving a high, the pullup resistor value is 4 kΩ and
when driving a low, the pullup resistor value is 40 kΩ.
The document then gives examples of what different sized pull-ups/pull-downs will do to the output voltage, but uses the TXS0108E as the reference example (which is behaves differently than the other three chips).
Summary: pull-ups okay for TXS010#, but pull-downs less than 50k-ohms very problematic.
The TXB010# includes an internal 4 k-ohm buffer for all parts.
Summary: Pullup and pulldown resistors of less than 50 kΩ must not be used with TXB translators because the internal 4-kΩ buffer and external resistors create a resistor divider network.
more to come...
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