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THVD1452: Query related to voltage level (VOH, VOL)

Rohidas Sawant76
Intellectual 380 points

Part Number: THVD1452

Hi !

I am using THVD1452 RS-485 transceiver IC in my design.

Supply voltage range specified in IC datasheet is -> 3 V to 5.5 V Supply Voltage.

I am operating this IC on 3.3V supply.

I want to know VOH and VOL voltage levels at 3.3V supply. In datasheet, they have specified it for only 5V. (section 7.7 Electrical Characteristics)

So, what are the voltage levels (VOH and VOL) for 3.3V ?  Please convey.

Regards,

Rohidas.

  • 0
    Guru 322000 points

    Only the typical values are only for 5 V. The minimum and maximum values are over the entire VCC range.

    (In any case, your load is likely to be much smaller than 8 mA.)

  • 0
    TI__Mastermind 26836 points

    Rohidas,

    Clemens's answer is correct - please note the beginning of the Electrical Characteristics section:

    The VOL values are defined without dependence on VCC, so 0.4 V is still the max assuming the recommended operating conditions are met. For VOH, there is a dependence on VCC, so the minimum value is VCC - 0.4 V, or in your case 2.9 V for a 3.3 V supply.

    Best,

    Danny

  • 0 in reply to Danny Bacic
    Intellectual 380 points

    Hi Danny,

    For VOH, My Vcc is 3.3V. Vcc tolerance is 3.3V±5%. So, worst case Vcc (min.) is = 3.135V

    i.e. VOH(min.) = 3.135 V - 0.4V = 2.735V.

    My MCU VIH (min.) = Vcc (max.) * 0.8 = 3.465V * 0.8 = 2.772V

    As per design requirement -> VOH (min.) > VIH (min.)

    But, it is not meeting my design requirement. Kindly guide further.

    Regards,

    Rohidas

  • 0 in reply to Rohidas Sawant76
    Guru 322000 points

    That VOH(min) value is for a load of 8 mA.

    Your MCU input is a high-impedance CMOS input with a very small leakage current, so the voltage drop will be much less than 0.4 V. For example, a leakage current of 8 µA will result in a VOH(min) of VCC - 0.0004 V.

  • 0 in reply to Rohidas Sawant76
    TI__Guru 53535 points

    Hi Rohidas,

    Clemens has a great point here. While all of the worst case values make it seem like requirements are not met, some worst cases only occur at predictable conditions, such as with very large output currents. With the only load on this output pin being a digital input of an MCU with presumably very low leakage (much less than 8mA), the output voltage will be very near Vcc. 

    Regards,
    Eric Schott