ZHCSH96H MARCH 2007 – May 2019 TPS40192 , TPS40193
PRODUCTION DATA.
Place two zeros at 50% and 100% of the resonance frequency to boost the phase margin before resonance frequency generates –180° of phase shift. For fRES = 11.7 kHz, fZ1 = 5.8 kHz and fZ2 = 11 kHz. Selecting the crossover frequency (fCO) of the control loop between 3 times the LC filter resonance and 1/5th the switching frequency. For most applications 1/10th the switching frequency provides a good balance between ease of design and fast transient response.
For this design
Because fCO < fESR the power stage gain at the desired crossover can be approximated in Equation 31.
PARAMETER | SYMBOL | VALUE | UNITS |
---|---|---|---|
First zero frequency | fZ1 | 5.8 | kHz |
Second zero frequency | fZ2 | 11.0 | |
First pole frequency | fP1 | 60 | |
Second pole frequency | fP2 | 500 | |
Midband gain | AMID(band) | 1.86 | V/V |
Approximate C2 with the formula described in Equation 32.
For a calculated value for C2 of 723 pF, the closest standard capacitor value is 1000 pF.
Approximate R10 using Equation 33.
For a calculated value for R10 of 2.65 kΩ, the closest standard resistor value is 2.61 kΩ.
Calculate R6 using Equation 34.
For a calculated value for R6 of 4.29 kΩ, the closest standard resistor value is 4.22 kΩ.
Calculate C1 and C3 using Equation 35 and Equation 36.
Using the a standard value close to 75 pF, select C1 = 100 pF. Likewise, using a standard value close to 6.5 nF, select C3 = 10 nF.
The error amplifier straight line approximation transfer function is described in Figure 18.