DC-DC step-down circuit example analysis, no more to learn out (dry goods)

Dc-dc circuits are often used when designing products. Recently, DC-DC circuits have been used in design. Let me introduce a wide range of applications and very practical DC to DC circuits. The solution used is MP2307 for MPS

MP2307 is an integrated BUCK regulator circuit with a wide input range of 4.75V~23V, adjustable output range of 0.925V~20V, maximum efficiency of 95%, and 3A with MOSFET of 100mohm. The current is quite powerful. And MP2307 is a 8pin SOIC package, and there are fewer peripheral devices. Often used in distributed power systems, network systems, FBGA, DSP systems, notebook computers and other products

Current control mode supports fast transient response and cycle-by-cycle current response. The fast transient response is easier to understand, that is, it is cut off instantaneously during overcurrent to protect the circuit. The cycle-by-cycle current response is the overcurrent, the current sampling is compared with the reference every time the chip is internal, the current value reaches the set voltage, the pulse is turned off, and the pulse is re-issued in the next cycle. In this way, the current is not increased and the protection is provided. But this method is different from snoring. Cycle-by-cycle is the PWM limit for each switching cycle, indicating that there is a small duty cycle PWM for each switching cycle. The snoring is to send a PWM, stop for a period, there is no PWM when the machine is stopped

MP2307 has an adjustable soft start to prevent magnetizing inrush currents caused by the on or off mode. Here is a talk about how the magnetizing inrush current is generated. Since the inside of the transformer is the principle of electromagnetic induction to convert the low voltage into a high voltage, or the high voltage becomes a low voltage, the transformer closing device generates an exciting current

So how does MP2307 work internally? We can see it through a graph. The MP2307 uses a current controlled mode to regulate the output voltage. The output voltage is measured by the FB pin through a resistive voltage driver and amplified by an internal transconductance differential amplifier. The voltage at the COMP pin is also compared to the internal switch current without the voltage of the control output. The converter uses an internal N-channel MOSFE switch to regulate the output voltage by reducing the input voltage

Since the high side of the MOSFET requires a higher gate voltage than the input voltage, a push capacitor is required to connect the SW and BS pins to drive the high side gate. This push capacitor starts charging from the internal 5V when SW is low. When the voltage of the FB pin exceeds 20% of the specified value of 0.925V, the overvoltage comparator will trigger the COMP pin and the SS pin to discharge to GND, forcibly closing the high side

The author also drew a schematic and PCB according to the reference design:

PCB layout needs to consider the size of the current through, MP2307 supports up to 3A, the place of high current is properly thickened, and the FB pin needs end feedback

Altium’s PCB 3D view is still beautiful, there are wood

The calculation of the voltage output value is relatively simple Vout=0.925x(R1+R2)/r2. R2 can be set up to 100k, but we usually use the typical value of 10k. The R1 and R2 configurations of the common output voltage are listed below

Also, share a trick to increase power conversion efficiency. Efficiency can be increased by adding a bootstrap diode between the BS and the output. However, there are applicable conditions that satisfy 1. The output voltage is 5V or 3.3V and the duty ratio is greater than 65%, that is, the output voltage/input voltage is greater than 65%, which is applicable

The author also shared the above schematic and PCB, and forwarded this article, and pay attention to the post-private letter “DCDC” to obtain schematic and PCB data