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LSF0108 translation 1.8V/3.3V

ILS
Prodigy 160 points
Other Parts Discussed in Thread: WL1837, AM5716

I am using an LSF0108 to translate between 1.8V to 3.3V

On the 1.8V side is connected to WL1837 WiFi card - SDIO interface (CLK, CMD, D0-D3)

On the 3.3V side is connected to AM5716 processor to mmc3 interface

I can't get it work for frequencies greater than 10 MHz

What are the correct pull-up values for both sides?

Every pin need pull-up?

Right now i have 1kOhm pull-ups on 3.3V side and 500 Ohm pull-ups on 1.8V side

  • 0
    TI__Expert 6335 points

    I have assigned this to the appropriate apps engineer. They will get back to you.

    Do you have oscilloscope waveform captures that you can share?

    Also, did you review Section 9.2.1.2.2, which describes how to choose an appropriate pull up resistor value?

  • 0 in reply to Nirav Patel
    TI__Guru 62160 points
    Hi ILS ,

    The pull up resistor values are dependent on the total current which the host side could be able to handle .The other consideration would be the data rate which could be achieved by the pull up values depending on the RC time constant . The higher pullup resistor would result in lower overall datarate . If the host side is open drain , you will need pull up ,otherwise , there is no requirement for the pullup resistor.
    for 10Mhz , the R can be calculated by :
    f = 1/(6*RC)--> 6 RC will be for full cycle of charge and discharge .
    assuming a load cap of 10pf , R = 1.67 kohm. The load cap needs to be small enough so that the resistor is high enough and the Vol will be within the acceptable range. With 30pf load cap , the R will be 555ohm which will increase the IOL at the host side .

    with 1.67Kohm pullup resistor , the host side driver should be able to handle (3.8V- 0.3)/1.67kohm = 2.1mA of IOL current and be within 0.3V of Vol at the output .