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LSF0204-Q1: Circuti review and Question

Ryota Seki
Prodigy 30 points

Part Number: LSF0204-Q1
Other Parts Discussed in Thread: LSF0204

Our partner company is about to implement the circuit shown below.
Please allow me to confirm the following 1 to 3.
Thank you in advance.

1. Logic level of Signal_A1
If Signal_B1 is High by pull-up(R3), will Signal_A1 be 1.8V in this circuit?
Background: Originally there was a pull-up instead of C1, but they are trying to replace the resistor with C1 to prevent overshoot when Signal_A1 goes from Low to High. The purpose is to channel the high frequency component of the overshoot to the power supply.

2. Logic level of Signal_B2
Signal_A2 has a pull-down and Signal_B2 has a pull-up.
Is it possible to prevent intermediate voltage due to resistive voltage divider as long as the source device is outputting High/Low with sufficient drive strength?

3. Behavior while Vref_B is turned on and the voltage is rising to 3.3V
While Vref_B is turned on and the voltage is rising to 3.3V (during the period below), what is the state of port B of LSF0204?
SignalA2 is driven low by the source device before Vref_B is turned on. I want to specifically check if Signal_B2 can stay low during the period when Vref_B is rising.
Vref_B = 0V
0V < Vref_B < Vref_A
Vref_A < Vref_B < Vref_A+0.8V

 

Application circuit
*Vref_B(3.3V) turns on after Vref_A(1.8V) turns on completely.
Application circuit _LSF0204-Q1.png

  • 0
    TI__Mastermind 48511 points

    Hi Seki-san,

    1. A-side will also be high if B-side is idle through the use of the external pullup. If either side decides to drive low however, the opposite side will follow and the bus will drive low.

    2. Due to the open drain nature of this device's I/Os, it is not suggested to use pulldown resistors. In the event that signal A2 is used as output, it will never be able to fully reach 1.8V due to external pulldown. If pulldown is mandatory, I would recommend  a different device altogether that is more compatible with external pulldowns, i.e TXU0x04-Q1. 

    3. In this case, if A2 is driving/ maintaining a low state with VREFA/ EN biased to 1.8V already, B-side will also see a logic low state. 

    For additional information about the functionality of this device, please see https://www.ti.com/video/series/understanding-the-lsf-family-of-bidirectional--multi-voltage-lev.html.

    Regards,

    Jack