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LM2904-Q1: How the actual application circuit works

Cherry Zhou
Mastermind 22235 points
Part Number: LM2904-Q1

Hi team,

The figure above shows a circuit to control the output voltage by adjusting the PWM duty cycle.

Where FTM2_blower is the PWM input, P_BAT is the fixed 12-V supply, is_FB_blower is the adjustable voltage input, and DA_blower_CTR is the adjustable voltage output. (Is_FB_blower and DA_blower_CTR correspond to the gate and drain of the MOS tube, respectively. The control diagram is shown in the figure below. The blower motor is also connected to the 12 V supply at the top. The speed control module can be simply understood as MOS tube. Is_FB_blower corresponds to VF-BL, BL_Ctrl corresponds to DA_blower_CTR)

The customer would like to know how the circuit shown above works and how the dynamic adjustment is calculated or how the static design is calculated. Thanks.

Best Regards,

Cherry

  • 0
    TI__Genius 12820 points

    Hi Cherry, 

    Could you re-upload the circuit that you are referencing in the beginning? I am unable to view the image attached in the thread. 

    Thank you!
    Best Regards,
    Ashley

  • 0 in reply to Ashley Kang
    TI__Mastermind 22235 points

    Hi Ashley,

    Thanks for your support and please see the circuit below:

    Thanks and Regards,

    Cherry

  • 0 in reply to Cherry Zhou
    TI__Genius 12820 points

    Hi Cherry, 

    Thank you for sharing the schematic. Have a few questions to clarify: 

    • What is the function of C84? Populating a capacitor between the input pins could cause some instability so it is not recommended. 
    • What is the expected input for the PWM input (FTM2_Blower) and the other input (IS_FB_Blower)? You mention IS_FB_Blower is an adjustable input but is there a range of voltages it is expected to be?  

    Please let me know if you have any questions.
    Thank you!

    Best Regards,
    Ashley

  • +1 in reply to Ashley Kang
    TI__Genius 12820 points

    Hi Cherry, 

    Is there any updates with the questions or additional information the customer can provide? In the meantime, I will set my answer as "TI Thinks Resolved" but please feel free to add to this thread or contact us with any questions. 

    Thank you!
    Best Regards,
    Ashley