Some time again, I revealed the Design Thought (DI) “Easy PWM interface can program regulators for Vout < Vsense.” It confirmed some easy circuits for PWM programming of normal bucking-type regulator chips, each linear and switching, together with functions that want an output voltage span that may swing effectively under the regulator’s sense voltage.
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Current reader feedback have proven curiosity in making use of these designs to completely different functions and regulators. So, right here’s a step-by-step process to make that course of simpler.
Be aware that it solely works if Vx > 2Vs and Vl > Vs.
Determine 1 Ten discrete elements comprise a circuit for linear regulator programming with PWM.
The steps are:
- Vs = U1 sense voltage from U1 datasheet (sometimes 0.5 to 1.25 V)
- Vl = accessible logic rail (sometimes 3 to five V)
- Vx = desired most output voltage at PWM obligation issue = 100%
- Vpp = PWM peak to peak amplitude, sometimes Vl
- Fp = PWM rep fee
- N = PWM bits of decision, N > 4
- R1 = advisable worth from U1 datasheet instance utility
- R2 = R1(Vx/Vs – 1)
- R4 = R2Vl/Vs – R1 – R2
- R5 = (Vl – Q2vbe)Q2minbeta(R4 + R1 + R2)/Vl
- R3 = Vpp/(Vs/R1 + (Vl – Vs)/(R1 + R4))
- R3C3 = R2C2 = 2((N-2)/2)Fp-1
- C1 = C2R2/R1
Now, taking the cheap XLsemi XL4016 asynch buck converter for instance case for U1, and turning the crank for these givens provides you:
- Vs = 1.25 V
- Vl = 3.3 V
- Vx = 30 V
- Vpp = 3.3 V
- Fp = 10 kHz
- N = 8
- R1 = advisable worth from U1 datasheet determine 4 = 3.3 kΩ
- R2 = 75 kΩ
- R4 = 120 kΩ
- R5 = 15 MΩ
- R3 = 8.2 kΩ
- C3 = 0.1 µF, C2 = 0.011 µF
- C2 = 0.27 µF
This yields Determine 2.
Determine 2 Basic design-accommodating parameters listed above. Be aware that U1-specific elements (e.g., inductor, capacitors, and energy diode) are usually not proven.
Be aware that if the microamps and millivolts of residual zero offset that persist on the unloaded provide output at PWM = zero obligation issue aren’t objectionable, then the Q2 R5 present sink is irrelevant and may be omitted.
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Associated Content material
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- Three discretes suffice to interface PWM to switching regulators
- Cancel PWM DAC ripple with analog subtraction
- Add one resistor to permit DAC management of switching regulator output
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