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Original question:

ULN2003A: Can you provide figure of "Maximum Collector Current vs Duty Cycle" for PW package?

ULN2003A: Thermal performance and max drive current

Michiaki Tanii
Expert 4640 points
Part Number: ULN2003A

 

Hi team,

 

Our customer is make sure on the way of consideration for thermal performance.

 

I think customer can estimate from thermal resistance, so customer could get Pd = (Tj - Ta) / theta Ja.

But in the datasheet, Figure 4 and 5 show the maximum collector current related duty cycle and number of outputs.

 

How should we use these figure and how long is duration of 100% duty cycle ?

 

Thank you and best regards,

Michiaki

  • 0
    TI__Genius 13760 points

    Hi Michiaki,

    Thank you for reaching out to the E2E forum!

    When considering thermal performance there are a couple things that you must consider. The maximum power dissipation on this device is obtained by the equation that you have listed in the question: Pd = (Tj - Ta) / theta Ja. Theta JA is the junction to ambient thermal resistance that can be found in section "6.4 - Thermal Information" in the datasheet. It varies depending on the part being used.

    In order to find the power dissipation according to your application you must use the first equation in section "9.2.2.3 - Power Dissipation and Temperature". Pd is power dissipation, Voli is OUT pin voltage and ILi is load current. The equation is the summation of power dissipation across all of the channels being used. This value must not exceed the value obtained from Pd = (Tj - Ta) / theta Ja.

    Figure 4 and 5 from the datasheet must be considered when calculating the power dissipation across each channel. The duty cycle and number of channels used will dictate the amount of current you will be able to use in the system and will ultimately impact the total power dissipation in the device.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Expert 4640 points

    Hi Andy,

    Could you kindly advise the time at 100% duty cycle ?

    I think the time of 100% duty (or frequency) would be specified.

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Genius 13760 points

    Hi Michiaki,

    The duty cycle is the cycle of operation for your application and depends on the the design specifications (i.e. the percentage of time that the device will be ON in a chosen time period). 100% duty cycle means that your device will be on all the time.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Expert 4640 points

    Hi Andy,

     

    In your explanation, the time of on duty is specified by customer.

    When the frequency is very low (i.e 1kHz), the on time of 100% duty is 1msec.

     

    If customer configure at 50% duty, on time is 500 usec.

    But when the frequency is configured high (i.e 1MHz), the on time of 100% duty is 1 usec.

     

    In your explanation, if customer configured low frequency, ULN2003 could drive larger current.

     

    Is my understanding correct ?

    Please let me double check on your answer.

     

    Thank you and best regards,

    Michiaki

  • 0 in reply to Michiaki Tanii
    TI__Genius 13760 points

    Hi Michiaki,

    The frequency only changes the period, or cycle time of the signal. For example, with a frequency of 1kHz each period will be 1ms. A frequency of 1MHz will have a period of 1us and so forth. The duty cycle dictates the percentage of time within that period that the part will be on and off. This means that no matter the frequency, 1kHz or 1MHz, 100% duty cycle still means the device is always on. 50% duty cycle means that the in each period the device will be on on for half of the period and off for the other half of the period. If you average the time that the part was on and off over a minute for example, you will still get that the device was on for 50% of the time and off for the other 50%.

    To answer your question, the frequency does not affect the amount of current you can drive, but the duty cycle does. You can drive larger currents by keeping the duty cycle low. You can observe how the duty cycle affects the current in Figures 4 & 5 of the datasheet.

    Regards,

    Andy Robles