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ULN2003A: ON-state input voltage

Part Number: ULN2003A

Hello,

 

Regarding to the ON-state input voltage on ULN2003A, my customer is asking some question.

When input is opened, output collector is on. (Ic=5mA) and they will decide register R on input side.




(Question)

(1) About ON-state input voltage (datasheet page5),

Is it meaning that it is VIH(TTL/CMOS) for output collector is on?

Or when Ic=200mA, they should input less than 3V for output collector is on?

 

 

(2) They will use Ic=5mA as collector current.

When Ic=5mA, how will ON-state input voltage become?

They think that it will be smaller compare with case of Ic=200mA.

If so, how many voltages will it be become? Their understanding is correct?

And when they use high-current transistor array for low current operation,

is transistor array switched with no problem?

 

(3) About Figer6. (datasheet page 9),

In case of ULN2003A, maximum input voltage is 3V

From Figer6., when input is 3V, input current is about 500mA(typ) and about 900mA(max).

(input current)

・Typical(500mA) -> It is needed for output collector is on?.

Maximum(900mA) -> Current limit for input? Or Maximum of needed current for input?

 


 

Regards,

Tao2199

  • Hello Tao_2199,

    Hope your day is going well.

    My responses are numbered coinciding with your questions.

    1. The Vi(ON) voltage needs to be above 2.4V for the output to turn on
    2. Even at 5mA, Vi(ON) needs to be above 2.4V
      1. it is fine to use a high current device for low currents
    3. The plot shows input current in micro amps (uA) not milli amps (mA)
      1. the typical value is the current needed to run the device in normal operating conditions
      2. the maximum value is the current needed to run the device in extreme operating conditions (high temperature, for example) 

    If you have any other questions, let me know.

    Best,

    Nick

  • Hello Nick,

     

    Thank you for reply.

     

    My customer understood about answer from you.

    As additional question.

     

    (Question)

    (1)They designed the following schematics as switch circuit.

     

     

     

    When Ry=10k,Rx=12k, Vi is 3V to 4V. (Ii = (24V-Vin)/(12k+10k))

    (According to figure 6.,Input current : 910uA@Vin=4V, 955uA@Vin=3V)

    So They think that their circuit is satisfied as specification of ON-state input voltage.

    Their understanding is correct?

     


     

     

    (2)About you mentioned last answer(3.a, b),

    a. the typical value: in normal operating conditions

    -> It’s meaning at TA 25℃ conditions?

    My understanding is correct?

     

    b. the maximum value : in extreme operating conditions 

    -> It’s meaning at TA -40℃ to 70or -40 to 105conditions?

    If TA=-40℃ to 105, their estimation (Item 1: above) is correct?

    (They use ULN2003A (TA -40℃ to 70).)

     

    Regards,

    Tao2199

  • Hello Tao2199,

    I've numbered my responses like before.

    1. With Ry = 10k and Rx = 12x, Vi should be ~2.65V and Ii should be ~970uA (This satisfies the maximum requirements of the part to operate)

    2a. Correct, normal operating conditions mean 25C

    2b. The plot is a general figure meant for all 6 parts on the datasheet. The plot shows Tj in the upper left corner, this is junction temperature. The part is rated up to 125C junction temperature.

    If you have any other questions, let me know.
    Best,
    Nick
  • Hello Nick,

     

    Thank you for reply.

    I have a question about last your answer (item1).

    “With Ry = 10k and Rx = 12x, Vi should be ~2.65V and Ii should be ~970uA.

    970uA = (24V 2.65V/12k ohm + 10k ohm

     

    (Question)

    (1) I think that Vi=2.65V and Ii=970uA are led with above formula.

    In this case, which parameters(Vi and Ii) are variable or solution?

    For example;

    If Ii=970uA is base as variable, how is it led?

    According to Fig 6., Ii is 970uA at Vi=3V on maximum input current curve.

    I need to consider Vi=3V as maximum input voltage?

    My understanding is correct? Or is it led as other reason?

    Also if Vi=2.65V is base as variable, how is it led?

    I cannot make it clear yet and

    could you please tell me about your answer (item1) in more detail?

     


     

    Regards,

    Tao2199

  • Hey Tao_2199,

    I believe the below points should take you through the solution.

    1. "which parameters(Vi and Ii) are variable or solution"?

         - Rx and Ry are variables, both Vi and Ii are your solutions

         - The control that you have over Vi and Ii depends on your resistor values Rx and Ry

    2.  Vi is dependent on the resistor values that you choose for Ry and Rx and follows the below equation

    Vi = 24V * (2.7k / (2.7k + Rx + Ry))

         - Where: 24V is your voltage rail and 2.7k is the internal resistance to the device (see figure 20)

    3. Ii is dependent on Vi, Ry, and Rx. Based on the below equation

    Ii = (24V - Vi) / (Rx + Ry)

         - The li term is the maximum current that your voltage rail can supply into the device.

         - At 2.65V the device will require ~800uA maximum and your rail can supply 970uA maximum

    This means that your voltage rail meets the requirements of the device for it to operate.

    I hope this helps!

    Best,

    Nick

  • Hi

    Excuse me for cutting in.

    I think the requirement is to define the Iin value when the transistor is on, right?

    According to the previous answer, Vi(on) requires the voltage above 2.4V.
    And the total input resistance of ULN2003A would be 12.9Kohm from the internal block diagram.

    So at least, requirement input current can be let by 2.4/12.9K = 186uA. Is my understanding correct?

    Bestregards
  • Hello na na78,

    The input resistance of the ULN2003A should be calculated with just the base resistor, Rb, which is 2.7kOhm, as seen in the image below.

    Based on Figure 6, at 2.4V the device will need, typically, ~350uA.

    Best,

    Nick

     

  • Hi Nick

    Thank you for reply.

    Do you mean the following based on Figure 6?

    Typical Iin(on) = ~350uA @ Vin = 2.4V
    Maximum Iin(on) = ~750uA @ Vin = 2.4V

    So, I think we need at 750uA input current in order to keep the transistor always on in any operating condition.
    Is it correct?

    By the way, do we need hfe characteristic for calculation of minimum Ii condition to set the transistor on?

    BestRegards
  • Hi na na78,

    Yes, it is best to design the input supply to meet the maximum requirements of the device.
    Yes, if you use 2.4V input voltage and have 750uA input current the device will be within proper operating conditions.

    The typical Ii value should be treated as a minimum when designing with this part.
    If the supply cannot meet the typical Ii value, the device may not operate as intended.

    Best,
    Nick