LSF0204: Interface reference design

Allen Lu

Part Number: LSF0204
Other Parts Discussed in Thread: , TXU0304, SN74AXC4T774, TXS0104E

Hi team :

My customer is using LSF0204 to transfer the SPI signals, and setting as below:

VREFA:1.8V, VREFB:3.3V, EN:1.8V，but during the development ,we found that the voltage level from A to B is 1.8V-1.8V, but not 1.8V-3.3V.

does it means we need the pull-up resistor instead?

if we can`t change the PCB due to the MP schedule, any P2P device can be used in this case within the internal pull-up resistor?

And according to this description :The LSF0204-Q1 device supports level translation applications with transmission speeds greater than 100 MHz using a 200-Ω pullup resistor with a 15-pF capacitive load.

does this 100Mhz support each channel as 20Mhz per channel or 100Mhz per channel?

Allen Lu

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 318760 points

The LSF always requires pull-up resistors. There is no P2P device.

It does support 100 MHz per channel, but only if the other devices can drive the current through the 200-Ω pullup resistors.

SPI uses unidirectional signals. You should use a buffered translator like the TXU0304 or SN74AXC4T774.

0 Allen Lu over 3 years ago in reply to Clemens Ladisch

TI__Intellectual 2700 points

Hi Clemens:

tks for your explanation. but i found that the TXS0104E is P2P device within internal pull-up resistor as 14-Pin TSSOP, but with different Maximum Data Rates, does it work this SPI application without changing the PCB?

0 Allen Lu over 3 years ago in reply to Allen Lu

TI__Intellectual 2700 points

And does the TXS0104E support 24Mbps per channels? And the customer set the SPI rate as 20Mhz,does it works on this application?

0 Clemens Ladisch over 3 years ago in reply to Allen Lu

Guru 318760 points

Sorry, you are correct that the TXS0104E is P2P, and OE is referenced to the lower voltage.

The TXS can work, if you stay below 24 Mbps (= 12 MHz), and if your other devices meet the requirement in section 8.3.2 of the datasheet.

0 Allen Lu over 3 years ago in reply to Clemens Ladisch

TI__Intellectual 2700 points

tks Clemens for your confirmation, it is helpful and there is another points according to the 24 Mbps (= 12 MHz), does it means the bus is 2bit , such as 0 and 1?

+1 Clemens Ladisch over 3 years ago in reply to Allen Lu

Guru 318760 points

No. One complete cycle of a square wave consists of two bits, high and low.

0 Allen Lu over 3 years ago in reply to Clemens Ladisch

TI__Intellectual 2700 points

Hi Clemens:

There is another concept about transmission speed that I want to confirm with you, and this concept also confuses customers.

TXS0104E： 24Mbps

LSF0204: 100Mhz

would you share why there are two units for the speed rate data ,it there any common description?

And the datasheet doesn't say that this speed is per channel or the sum of the entire device. hope to get some statement for the customer explanation.

0 Clemens Ladisch over 3 years ago in reply to Allen Lu

Guru 318760 points

I wouldn't know why the datasheets are written in the way that they are written; I am not a TI employee.

The speed is per channel.

0 Dylan Hubbard over 3 years ago in reply to Clemens Ladisch

TI__Mastermind 46555 points

Hi Allen,

These are just two ways to write the same thing. The LSF device is more highlighting the BW capabilities of the family, which is a better way to represent the speed for that device since it essentially and analog switch.

Logic

Logic forum

LSF0204: Interface reference design