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I am making a driver PCB to drive an XHP70.2 LED at 15A (~7v) Continuous, Controlled from an Arduino. I am new to OpAmp's so I would like to know:

  • Does this circuit look as though it would function as intended (as a current source for 15A@7v from a 2S Li-ion, controlled by an Arduino PWM pin)?
  • Would 1.5mOhm (1W 2512 [6432 Metric] Thick Film) be a suitable value for RSENSE?
  • What OpAmp would be best?
  • What values would be needed for R1, R2,...R8? (& C1)
  • Would (CSD16340Q3)'s be suitable for U1 & U2?

CSD16340Q3 - http://www.ti.com/lit/ds/symlink/csd16340q3.pdf

NCP3420 - https://www.onsemi.com/pub/Collateral/NCP3420-D.PDF

LTC6992 - https://www.analog.com/media/en/technical-documentation/data-sheets/LTC6992-1-6992-2-6992-3-6992-4.pdf

If it will work, are there any possible improvements? i.e. reducing the number of components

Diagram of Circuit Plan

Thank you in advance

Wizzard_Dr
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1 Answers1

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You need to compute some common-mode and differential voltages.

I use 50mV for max current to choose the current sensor. For smaller power you might be able to use say 20 or 25 mV FS but your R ratios need to be low error 0.5% or better have matched gain ratio arrays for high CMRR noise rejection. Note: Very layout sensitive for high gain. And logic loops on schematic need to be physically as small as possible with stray inductance and high gain. (~100~200)

Then use R4/R2=R3/R1 for gain. Check Vcm min~max to make the inputs within Rail-to-Rail or else move the sensor to the ground side of the load and choose any dual PNP input Op-Amp to sense near 0V.

The next stage might use equal R values for unity gain.

Tony Stewart EE75
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