Shiwei wide voltage 9-100V 2.6A step-down constant current driver IC LED car light solution-EEWORLD

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Application Information

Output current

The output current is sampled by the error amplifier inside the chip and compared with the internal reference voltage and the error is amplified, thereby achieving constant current control of the system. The output current formula is as follows: Iout=176mV/RCS

◆Chip work

After the system is powered on, the capacitor connected to the power pin VDD is charged through the startup resistor. When the power voltage is higher than 3.4V, the chip circuit starts to work until the VDD port voltage stabilizes and reaches the clamping voltage of about 5.4V. The power supply current of the chip is mainly provided by the resistor RVDD connected to the VDD port.

◆Inductor selection

In order to ensure the constant current accuracy, it is necessary to select a suitable inductor so that the inductor works in continuous current mode. The critical value of the inductor is: To ensure the output constant current characteristics of the system, the inductor value selected in the application should be greater than LBCM, and the inductor current should work in continuous mode.

◆MODE setting

Function MODE

Full light hanging

Half bright VDD

◆Over temperature protection

The chip has a built-in intelligent over-temperature protection circuit, which gradually reduces the output current as the temperature rises, preventing the circuit from being burned out due to over-temperature and preventing abnormal lighting caused by sudden current shutdown.

◆Freewheeling diode

Note that the rated average current of the freewheeling diode should be greater than the average current flowing through the diode. The average current calculation formula is as follows:

Note that the diode should be able to withstand the reverse peak voltage. It is recommended to select a diode with a reverse rated voltage greater than VIN. In order to improve efficiency, it is recommended to select a fast recovery Schottky diode.

◆VDD supply resistor

The chip mainly provides the working current of the chip through a power supply resistor RVDD to the chip VDD. Usually, VDD meets

VDDVINIDRVDD

It can be seen from the formula that if RVDD is too large, the system will be underpowered, and if it is too small, it will cause excessive power consumption and chip overheating. The typical value of IVDD is 2mA. If the input capacitance of the MOS tube is large, the chip operating current will increase, and the power supply resistance value should be reduced accordingly.

◆VDD bypass capacitor

The VDD pin needs to be connected in parallel with a bypass capacitor of 0.47uF or more. When laying out the PCB, the VDD capacitor needs to be placed close to the port.

◆MOS tube selection

The MOS tube withstand voltage should be higher than 1.2 times the input voltage; the MOS tube current IDS is generally required to be more than 2 times the maximum peak current of the inductor. The smaller the on-resistance RDSON of the MOS tube, the smaller the power loss in the MOS tube, and the higher the efficiency of the system conversion. The MOS tube threshold voltage VGS should be selected at a lower threshold voltage value. The chip power supply operating voltage determines the DRV drive voltage. Usually the chip drive voltage is 5.4V, so it is necessary to ensure that the MOS tube can be fully turned on when VGS equals 5.4V.

◆PCB design considerations

1: The copper wiring between the chip SW terminal and the freewheeling diode and power inductor should be as short as possible and have a large line width. 2: The copper wiring between the chip SW terminal and the CS current sensing resistor, and the copper wiring between the CS current sensing resistor and the input capacitor GND should be as short as possible and have a large line width. 3: The VDD capacitor of the chip is close to the chip layout, and the GND end of the VDD capacitor and the GND end of the CS current sensing resistor are connected at a single point. 4: The input capacitor of the system should be as close as possible to the AP5125 system layout to ensure that the input capacitor achieves the best filtering effect.

Power chip features

◆Wide input voltage range: 9V～100V

◆Fixed operating frequency: 140KHZ

◆Settable current range: 10mA～6000mA

◆Built-in frequency jitter circuit to reduce EMI interference to other devices

◆Average current mode sampling, higher constant current accuracy

CS voltage: 176mV

◆Output short circuit protection

◆Over temperature protection

◆Function mode: full brightness/half brightness

◆Built-in voltage regulator

◆SOT23-6 package