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LSF0108: LSF0108 USE？

Simba Su
Intellectual 430 points
Part Number: LSF0108
Other Parts Discussed in Thread: TXU0101, TXU0102

Tool/software:

1、It is required to achieve 3.3V to 5V PWM square wave output, using the recommended leakage circuit, FPGA leakage output, 3.3V power supply on the A-side, and 1.5K pull-up resistance; B side is connected to 5.0V power supply, the pull-up resistance is 1.5K, and the EN pin is 200K; The current A side output 3.3V high voltage, B side high voltage is less than 5V, only 4.6V, the current A side output low level, the actual test B side voltage of 4V, the actual test is as follows, yellow, green and blue are respectively B side, EN foot, A side measurement, why do such problems occur?

2、It is required to achieve 3.3V to 5V PWM square wave output, using the recommended leakage circuit, FPGA leakage output, 3.3V power supply on the A-side, and 1.5K pull-up resistance; B side is connected to 5.0V power supply, the pull-up resistance is 1.5K, and the EN pin is 0Ω. Measured when the A side is 3.3V PWM square wave, the B side is followed by A high level 3.3V square wave. At this time, the 3.3V supply current of the test A side has a relatively large fluctuation, up to 40mA. If the B side signal can use 3.3V signal, what is the risk of long-term operation?

3、It is required to achieve 3.3V to 5V PWM square wave output. FPGA adopts push-pull output, A side is not connected to pull resistance, directly connected to LSF0108, B side is connected to 5.0V power supply, pull up resistance is 1.5K, when the A side to 100K 3.3V PWM square wave, the test found that the B side can achieve square wave following, but can only maintain more than 20 s, what causes this problem?

  • 0
    Guru 316420 points

    The LSF is a passive switch. For correct operation, you have to take into account the analog properties of all connected devices, and if the driver does not have enough drive strength, achieving the desired speed might not be possible.

    Better use a buffered translator like the TXU0101/TXU0102/TUX0104.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 39916 points

    Hi Simba,

    The team is out on US holidays today and responses will be delayed. Thank you for your patience.

    Regards,

    Jack

  • 0 in reply to Jack Guan
    TI__Mastermind 39916 points

    Hi Simba,

    Clemens' is correct here- the logic high state is achieved through the external pullups with the transition edges based on the RC of the pullup and output cap. used. Using a buffered translator will help drive these edges and provide improved signal integrity. 

    Simba Su said:
    but can only maintain more than 20 s, what causes this problem?

    I am not sure what the concern is here, can you please elaborate? What is the output voltage reading of B-side in relation to A-side input? 

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Intellectual 430 points

    At the beginning of operation, the A side is 3.3V PWM square wave, the B side is 5V PWM square wave, after 20s, the B side square wave begins to be abnormal, the high level is less than 5V, gradually becomes smaller to about 4v, and then fluctuates up and down

  • 0 in reply to Simba Su
    Guru 316420 points

    The high-level output voltage is determined only by the pull-up resistors. So this looks as if your power supply sags.