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tps61500 at 12v being driven by a 3v MCU

Elliott Johnson
Prodigy 100 points
Other Parts Discussed in Thread: TPS61500, TPS61500EVM-369

So, I'm using a tps61500 to drive a string of 1.5A LEDs in serial, I've implemented a similar circuit using the TPS61500EVM-369 using the supplied LEDs and a 3v power supply and 3v MCU to provide a PWM signal.  However for the 1.5A LEDs my calculations indicated a 9v or larger supply for the LED driver necessary.  The MCU is still 3v, so should i use a Voltage Translator to translate the PWM signal to 12v for it to register on the LED driver? and if so which one would be appropriate?

sincerely
Elliott Johnson

  • 0
    TI__Guru**** 166626 points

    To determine the maximum output voltage that can be driven from Vin=3V and providing 1.5A, you can do a power balance:  eff=(Vo*Io)/(Vin*Iin) where eff~=87% for Vin<5V and Iin=Ilim(min)=3A.  So, Vo(max)=0.87*3V*3A / 1.5A = 5.22V, which is only 1.5 LEDs.  If you have concluded that you need Vin=9V, then Vo(max)=15.7V so I suppose you have about 4 LEDs in series?

    Regarding your PWM signal driving EN like in datasheet Figure 1, the EN high threshold is 1.2V regardless of VIN so you do not need to do level translation.

  • 0 in reply to Jeff F
    Prodigy 100 points

    yes, that's what I calculated exactly, and thank you very much that’s exactly the information I needed.