IO Levels supported by USB-Serial Controllers - KBA90253

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Question: What are the IO levels supported by USB-Serial controllers?

 

Answer:

USB-Serial controllers have support for both CMOS (Input and Output) and LVTTL (Input only) IO levels.

  1.   CMOS: USB-Serial Controller supports both CMOS logic levels on input buffers and output drivers. Following are the logic level thresholds:  
        
    •     VIH = 0.7 * VDDD (for all the VDDD values)
    •   
    •     VIL = 0.3 * VDDD (for all the VDDD values)
          (Please note 1.71 V < VDDD < 1.89 V and 2.0 V < VDDD < 5.5 V)    

            

                                                                                                                                                                                                                  
              VOH (MIN) (V)        Conditions        VOL (MAX) (V)        Conditions
              VDDD-0.4        IOH = 4 mA,
              VDDD = 5 V +/- 10%
              0.4        IOL = 8 mA,
              VDDD = 5 V +/- 10%
              VDDD-0.6        IOH = 4 mA,
              VDDD = 3.3 V +/- 10%
              0.6        IOL = 8 mA,
              VDDD = 3.3 V +/- 10%
              VDDD-0.5        IOH = 1 mA,
              VDDD = 1.8 V +/- 5%
              0.6        IOL = 4 mA,
              VDDD = 1.8 V +/- 5%
        
    •  
  2.   LVTTL: USB-Serial Controller supports LVTTL levels on input buffer only. LVTTL levels are not supported on output drivers.
      Following are the logic level thresholds:  
        
    •     If VDDD < 2.7 V, VIH = 0.7 * VDDD & VIL = 0.3 * VDDD
    •   
    •     If VDDD >= 2.7 V, then VIH = 2 V and VIL = 0.8 V
    •