• State TI Thinks Resolved
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 22 subscribers
  • Views 90 views
  • Users 0 members are here
Support feedback
Options
Options
Related

TXB0104: Few level shifters issue

Josel Go
Expert 6515 points
Part Number: TXB0104
Other Parts Discussed in Thread: LSF0204, TXS0104E, LSF0204-Q1, TXU0304

Hello there,

You have few level shifters:

TXB0104,  TXS0104,  and LSF0204.

 

For TXB0104

7.3.2 Input Driver Requirements
Typical IIN vs VIN characteristics of the device are shown in Figure 7-2. For proper operation, the device driving 
the data I/Os of the TXB0104 device must have drive strength of at least ±2 mA.

 

 

For TXS0104 

8.3.2 Input Driver Requirements
The fall time (tfA, tfB) of a signal depends on the output impedance of the external device driving the data I/Os of the TXS0104E device. Similarly, the tPHL and maximum data rates also depend on the output impedance of the external driver. The values for tfA, tfB, tPHL, and maximum data rates in the data sheet assume that the output impedance of the external driver is less than 50 Ω.

 

For LSF0204

8.2.1.2.1.1 Pull-Up Resistor Sizing
The pull-up resistor value needs to limit the current through the pass transistor when it is in the ON state to about 15 mA. This ensures a pass voltage of 260 mV to 350 mV. If the current through the pass transistor is higher than 15 mA, the pass voltage also is higher in the ON state. To set the current through each pass transistor at 15 mA, to calculate the pull-up resistor value use Equation 1.


Rpu = (Vpu – 0.35 V) / 0.015 A (1)

Table 8-3 summarizes resistor values, reference voltages, and currents at 15 mA, 10 mA, and 3 mA. The resistor value shown in the +10% column (or a larger value) should be used to ensure that the pass voltage of the transistor is 350 mV or less. The external driver must be able to sink the total current from the resistors on both sides of the LSF0204-Q1 device at 0.175 V, although the 15 mA applies only to current flowing through the LSF0204-Q1 device.
The LSF0204-Q1 does not provide any drive capability. Therefore higher frequency applications will require higher drive strength from the host side. No pullup resistor is needed on the host side (3.3 V) if the LSF0204-Q1 is being driven by standard CMOS totem pole output driver. Best practice is to minimize the trace length from the LSF0204-Q1 on the sink side (1.8 V) to minimize signal degradation.

 

Now which level shifter I need to use if my driving capacity is only 1mA because the data sheet is not clear AT ALL.

Can you please help me????

Thank you 

Sorin Haidau

  • 0
    TI__Mastermind 44861 points

    Hey Sorin,

    What is the application use case? What interface are the signals, and are they auto bi-directional per channel? Are you looking for a buffer due to your input driving capability being only 1mA? Please provide more details here.

    The customer may also reference https://www.ti.com/lit/po/scea118/scea118.pdf?ts=1721063250652&ref_url=https%253A%252F%252Fwww.google.com%252F for suggested devices depending on the use case. 

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Prodigy 20 points

    Sorry for the incomplete information.

    We need bidirectional level shifter because we are using this for SPI interface. After my knowledge SPI is not a high speed interface.

    Buffer is not the case because buffer means unidirectional.

    How did you calculate those resistors values???

    Table 8-3. Pull-Up Resistor Values PULLUP RESISTOR VALUE (Ω)

    VDPU      15 mA          10mA            3 mA  NOMINAL +10%(1) NOMINAL +10%(1) NOMINAL +10%(1)

    5 V          310 341      465 512       1550 1705

    3.3 V        197 217      295 325       983 1082

    2.5 V        143 158      215 237       717 788

    1.8 V          97 106       145 160      483 532

    1.5 V           77 85         115 127      383 422

    1.2 V           57 63         85 94           283 312

    this is the LSF0204  data sheet for the pullup resistors calculation

    Now if I had the resistors value for 1mA would that be a solution????

  • 0 in reply to sorin Haidau
    TI__Mastermind 44861 points

    Hi Sorin,

    The pullup is calculated with the formula provided just above the table: 

    SPI is bidirectional, however it is fixed direction per channel, therefore a fixed direction translator such as the TXU0304 can be used as a robust solution by eliminating the need to add external pullups and saving space/ BOM. 

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Prodigy 20 points

    Hello Jack,

    You didn't answer the question.

    Do you (as TI) have any bidirectional level shifter (4 bit preferable) which can work with input current driving of 1mA not more???

    This is the question, not other solutions.

    Thank you Jack  

  • 0 in reply to sorin Haidau
    TI__Mastermind 44861 points

    Hi Sorin,

    TXS0104E and LSF0204 seem better suited for this application over the TXB0104 if you have input driving limitations of 1mA. In my previous response, I was suggesting the T XU0304 for the SPI signaling due to the direction configuration and easier implementation. The inputs are high-Z and factors such as the VT+ and VT- are also important considerations to ensure that a proper logic high/low input is interpreted by the level shifter.

    Regards,

    Jack