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Calculating upper and lower DAC references for a hysteretic controller of PowerPSoC device

Last Updated: 12/05/2011

How can one calculate upper and lower DAC references for a hysteretic controller of PowerPSoC device?

Example: Let the current through an LED string be 300mA with a ripple of 40%.

So Iavg = 300 mA.

Let the,

sense resistance value Rsense = 0.22 W

gain of CSA be 20 and,

the 8-bit DAC be set at a resolution of 2.6V/10mV.

Current sense voltage Vpeak = Ipeak x Rsense = 360 x 0.22 = 79.2 mV.

Similarly Vvalley= Ivalley x Rsense = 240 x 0.22 = 52.8 mV.

Corresponding to Vpeak and Vvalley, the output of CSA would be the gain multiplied by the voltage.

Hence,

V’peak = Vpeak x 20 = 1.584 V and

V’valley= Vvalley x 20 = 1.056 V.

Now, the peak or upper limit DAC reference is calculated as,

REFupper = (V’peak/2.6) x 256 = 156

Similarly, valley or lower DAC reference is,

REFlower = (V’valley/2.6) x 256 = 104

Related Categories: PowerPSoC® Power Controllers