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Voltage level shift between RS-422 AM26LS32AC and LSF0204

LP Kim
Intellectual 330 points
Other Parts Discussed in Thread: AM26LS32AC, AM26LV32, AM26LV32E, LSF0204, 74ACT11032

Dear members!

 

I will desing RS-422 Driver for encoder interface using AM26LS32AC but am faced with a problem related to I/O Level between AM26LS32AC and processor.

Q1) Voltage level sifter between AM26LS32AC and processor

 

Vout of AM26LS32AC is 2.5~2.7[V] but Vout-Max is over 3.3[V] by using conditions. 

I think that it add Voltage level shift LDS0204 between processor and AM26LS32AC.

 

LDS0204 didn't mention the range for VIN,VOUT related to port and mentioned  the range for EN Pin.

Please review the block diagram above.

 

Q2) I know that termination resistor is using 80~120[ohm] between Plus and negative line for AM26LS32.

      Because of differntial line voltage, I think that the general analog switch can apply to AM26LS32 differential line

      Could you recommend the suitalble  analog switch to change Max14761 that support +/-15V

 

Thanks

 

  • 0
    TI__Guru*** 140166 points

    LP,

    I will have our logic application engineer find best translator and analog switch.

    If you use the AM26LV32, AM26LV32C, or AM26LV32E  that run from 3.3V supply then you will not need the translator.

  • 0 in reply to Ron Michallick
    Intellectual 330 points

    Dear Ron Michallick

    Thank you for your  reply.

    AM26LV32 looks good for commond mode input voltage +/-7V.

    Some quesiton to choice ..

    Q1) Why isn't mention VOH(Max)  related to AM26LV32E?

          VOH(Min) is 2.4V under special case conditions. Is that no proble to interface processor I/O 3.3V Level without translator(voltage level shifter)?

         If VOH(Max) isn't mention, VOH(Max) is equal to VCC(=If ,3.3V)  

     

    Q2) If it must apply to AM26LS32AC with LSF0204 , Is that no problem?

     Q3) If VOH(Max) isn't mentioned at specification as 74ACT11032, How is know VOH(Max) for Recommend condition( No Absolute condiiton) ?  

    Q4) According to AM26LV32E , Could you explains graph? I don't know exactly. HIGH/LOW --> What

  • 0 in reply to LP Kim
    TI__Guru*** 140166 points
    LP Kim,

    A1) The VOH maximum is certainly less than VCC.
    A2) Yes, it will work. I suggest pull ups on both sides. The processor side needs it because it is the input. The AM26LS32AC needs it because it's TLL output isn't very high.
    A3) VOH always has a load that draws current from the device, therefore the data sheet assumes that VOH max being less than VCC is common knowledge and not needed to be stated.
    A4) The chart is in error. The X axis should be labeled "Logic Output Current" The chart shows that VOH and VOL are very close to VCC and Ground when the load is light (left side). It also shows that a short on the output will pass a lot of current, 38mA short to VCC and 42mA for a short to ground.
  • 0 in reply to Ron Michallick
    TI__Guru*** 140166 points
    LP Kim,

    Logic app recommends LSF0204 or LV4T125 both are equally good choices.
    We have no analog switch replacement .