Summary:For fixed frequency peak current mode PWM boost DC-DC converter. A design method of current loop compensation circuit with simple structure and easy integration is presented. The circuit's ramp generation circuit can V/I convert the voltage on the on-chip oscillator charge and discharge capacitor, and the resulting ramp current has stable characteristics and easy slope adjustment. The current sampling circuit body uses SENSEFET combined with optimized buffer. The stage and V/I conversion circuit reduce the loss while improving the sampling accuracy. The entire circuit can be implemented in a 0.6 μm 15 V BCD process. The simulation results by Cadence Spectre show that the circuit can effectively suppress sub-harmonic oscillation, the sampling accuracy is 77.9%, and the compensation slope accuracy is 81.5%.
Key words: slope compensation; current sampling; current mode; V/I conversion
O Introduction Fixed-frequency peak current mode PWM (Pulse Width Modulation) Compared with the traditional voltage mode control, DC-DC converter has the advantages of good transient response, high output precision and strong load capacity, so it is widely used. As an important analog unit, the slope compensation circuit and current sampling circuit are the basis of current mode PWM control and play an important role in the stability of the current loop in current mode control.
1 Circuit Structure Figure 1 shows the block diagram of a typical peak current mode PWM Boost DC-DC control system. When the voltage feedback signal of the voltage outer loop is sent to the PWM comparator through the error amplifier VE amplified by the error amplifier, a triangular wave or a trapezoidal sharp-angled composite wave whose peak value represents the peak value of the output inductor current and a peak of the current inner loop The signal VE is compared to obtain a PWM pulse turn-off threshold. which is: [3][4]
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