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LSF0108: LSF0108 pull up resistor setting

Part Number: LSF0108

Hi Team,

customer is evaluating the LSF0108 for Intel baytrail SOC(1.8v) and LPC(3.3v) level translator, attached is their circuit that they tried to use the 4.7k pull up resistor to 3.3v for LPC_CLK00/11 signals, and they found that the voltage level is about 1.56v that caused the LPC function doesn't work. Furthermore, they tried to change the resistor from 4.7k to 330 Ohm, the waveform shown the peak is 2.7v but the valley is 0.64v that voilate the LPC VIL spec requirement which is below 0.5v.

So, customer wants to ask product team how to tune the resistor value to achieve the waveform requirement as 3.3v peak/0v valley?
Please advise. Thanks.

Regards,

Arthur


  • Hi Arthur,

    There are two primary factors that can speed up the up-translation of the LSF0108. The pull-up resistance, and the line capacitance.

    Since they have already tried reducing the resistance and found that their driver cannot sink enough current to keep V_IL within the required spec, then reducing capacitance would be the next step. Would it be possible to reduce the capacitance on the 3.3V side of the translator? Typically this can be accomplished by reducing trace length and by eliminating ground plane directly underneath the traces.

    Additionally, attaching a scope probe will add 3 to 15 pF, and can significantly affect the signal integrity. A differential probe is recommended for best results.