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TPS61500: Vin= 3.4 - 4.2V, Vout= 12V/0.75A (DC Fan). Two CC outputs in parallel?

Robin Dripps
Prodigy 35 points
Part Number: TPS61500
Other Parts Discussed in Thread: TPS92390

Hi,

I have an application that requires a Li-Ion battery to drive two 12V DC centrifugal fans in parallel, placed at the end of a cable, 600mm from the driver IC.  0.375A per fan, so 0.75A in total.  I need to do speed control so I figured using an LED driver would allow me to do analogue dimming, which would reduce the likelihood of EMI radiating from the 600mm long cable.

1.  Is it feasible to drive a DC fan from an LED driver, rather than a string of LEDs?

2.  Is it feasible that the TPS61500 is capable of driving a 12V/0.75A load, from a 3.5V input?

My 'rough' calculations suggest:

Output Power = 12V * 0.75A = 9W

Assuming 85% Efficiency...

Input Current = (9W / 3.5V) / 0.85 = 3.03A  This looks very close to the switching limit of the device?

3. Lastly, should one TPS61500 device not be sufficient, would it be possible to place two TPS61500 CC circuit in parallel, outputs connected together and sharing a common sense resistor?

Thanks!

Robin

  • 0
    TI__Genius 13001 points

    Hi,

    Thanks for your consideration of TPS61500 firstly!

    1.I'm not familiar with DC fan. As you know, LED driver is a constant current regulator and should work with any loading requiring constant current.

    2.Yes, your calculation is right.

    3.We don't have similar application before and I can't guarantee this. Would you mind give me some time to deep dive?

    I think you may take a look at TPS92390 which is a 4-channel device with 200ma/ch. You can tie these four channels together to get as large as 800ma output current.

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 35 points

    Thank you for the quick reply Robin!  

    The TPS92390 hadn't come up in my parametric searches, but it looks very interesting.  The external switching MOSFET must allow for higher switching currents at low Vin, so that's helpful. 

    The device also offers lots of protection features.  The Power-Line FET offers over-current protection, which I was also looking to implement anyway.

    Presumably with all 4x "OUT" channels tied together, the 800mA max specification should be achievable from a 3.5V input?

    Let me know your thoughts on connecting two TPS61500 devices together, I will continue looking into the TPS92390 device.

    Thanks!

    Robin

  • 0 in reply to Robin Dripps
    TI__Genius 13001 points

    Hi,

    TPS92390/1(4 / 6 channels) are our latest devices and we believe they can bring more improvement to your system. Would you mind sharing your email address so I can follow your design about TPS92390/1? Thanks!

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 35 points

    Sure thing. Would it be possible to message you directly in order to share my email address?

  • 0 in reply to Robin Dripps
    TI__Genius 13001 points

    Hi,

    I'll accept the friendship request from you.

    Robin