TOP22-227 principle circuit diagram

Taking the TOP smart power switch as an example, the picture shows the schematic block diagram of the TOP22X series device . The TOP22X switch has only three leads. In addition to the drain lead and source lead of the power switch, there is also a feedback control lead. The operating frequency is 100 kHz, and the operating mode is voltage-type PWM. After detection, comparison, and amplification, the output voltage is converted into a current signal and injected into the feedback control line. The internal RE resistor converts the current signal into a voltage signal and compares it with the triangle wave to change the pulse width to achieve PWM modulation .

The current injected into the feedback control lead is divided into two parts: one part supplies the internal control circuit and drive circuit of the TOP switch; the other part is the PWM control circuit. The duty cycle decreases linearly as the control current increases. Changes in the output voltage change the current injected into the control lead and adjust the output voltage by changing the duty cycle . The internal shunt regulator separates the error signal current from the control lead current and turns it into a voltage signal through the resistor RE and enters the PWM comparator.

The TOP switch operating in PWM voltage mode also has a week-to-week peak current limiting function. Inside the TOP switch, the power MOSFET on-resistance Rus (ON) is used as the detection resistor. The current limit comparator compares the on-state voltage drop on the power MOSFET's on-resistance RDS(on) with the threshold voltage. When the on-state voltage is higher than the threshold voltage, the power MOSFF-FET is turned off to achieve peak current limiting. In the TOP switch, the current limit comparator is temperature compensated. As RDS(on) increases with temperature, the change in the peak current limit is minimized and remains approximately constant.

Figure: TOP 22-227 circuit schematic diagram

The MC333XX series of MOTOROLA's parent company is also a PWM voltage type device and also has a peak current limiting function. A measuring power MOSFET is used inside the device, and a current mirror is used to detect the current in the power switch to achieve peak current shutdown . This is a lossless current sensing method.