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# AP3012 performance parameters and basic application circuit analysis

AP3012 is an internal 1.5MHz fixed frequency oscillator released by BCD, a PWM DC/DC converter with current mode, and an internal overvoltage protection OVP function, its switching current reaches 500mA, and the appearance is SOT23-5 package.

1. AP3012 performance parameters

Input voltage range: 2.6 "16V;

Shut-off current: 1uA;

Quiescent current: 3.5mA;

Switching current: 500mA;

Switching frequency: 1.5MHz;

Overvoltage protection voltage: 29V;

Soft start time: 550uS;

Feedback detection voltage: 1.25V, the input current of the feedback terminal is typically 45nA;

With SHDN function, the highest SHDN voltage is 1.5V;

Built-in over-voltage protection function, over-voltage protection is 29V;

Built-in soft start function to reduce the inrush current of the circuit system.

2. Basic application circuit of AP3012 The output voltage is calculated by the following formula:

VO=1.25*(1+R1/R2)

3. AP3012's design ideas for LCD screen W-LED driver

At present, in the 5'-9'LED screen, the LED structure is 3*5, 3*7, 3*9 (the number of LEDs in series * the number of LEDs in parallel), so only the lighting when 3 LEDs are connected in series is required. The voltage can meet the LED lighting requirements. The typical forward voltage drop of W-LED is 3.3V. At this time, when three W-LEDs are connected in series, the required voltage is 9.9V. Since the LCD screen has a W-LED current specification of 20mA for each series channel, The voltage drop on the current-sharing resistor is about 0.2V. To reach the lighting specifications of the LCD screen, the input voltage required for the entire LCD screen is 10.1V.

At this time, adjust the voltage divider resistance of the AP3012 circuit to obtain the required voltage value.

Calculation of output voltage:

VO=1.25*(1+R1/R2)

AP3012 drive circuit for LCD screen W-LED: 4. Application of AP3012 in LCD screen bias circuit

(1), AP3012 positive and negative voltage generating circuit (1) The circuit structure is simple, but V- is about 0.3V lower than V+, and the output voltage is adjusted by a voltage divider resistor. The calculation formula:

VO=1.25*(1+R1/R2)

(2), AP3012 positive and negative voltage generating circuit (2) This circuit has one more Schottky diode than the previous circuit (1), but the positive and negative voltages are more symmetrical, and the output voltage is adjusted by a voltage divider resistor. The calculation formula:

VO=1.25*(1+R1/R2)

5. Features of AP3012

The application system of AP3012 is a non-isolated DC/DC converter circuit, which can work under the voltage condition of 2.6”16V. The output DC voltage is controlled by the voltage divider resistor at the feedback end to obtain the working voltage required by the load.

6. AP3012 power consumption and shutdown control

(1) Power consumption of AP3012

Since the circuit of AP3012 belongs to the non-isolated DC/DC converter circuit of STEP UP, the voltage difference between its input and output cannot be too small, otherwise it will malfunction:

For the LCD screen W-LED drive, the output voltage is about 10V. When the input voltage exceeds 8.5V, if the IC is in the Shut Down state at this time, the input voltage will directly pass through the boost inductor and Schottky diode to the output terminal , Will make the LCD screen W-LED dimly bright, and the circuit cannot be turned off. , The recommended input voltage is 5V.

If the input voltage is too high, it will also cause the AP3012 to increase its power consumption and generate serious heat, which will trigger the internal temperature protection circuit and make the system work abnormally.

(2) AP3012 shutdown control

For the circuit that requires the input voltage to be lower than a certain value and turn off the output, it is necessary to consider the voltage control of the SHUN terminal to achieve the purpose of low-voltage detection and shutdown IC operation. The circuit is as follows: Choice of R3 and R4:

VIN=V4*(1+R3/R4)--〉

VIN=0.4*(1+R3/R4)

Description:

VIN: The minimum shut-off voltage required;

V4: The minimum required voltage of SHUN.

7. AP3012 efficiency test

Test diagram: Calculation formula:

η=(VIN*IIN/VOUT*IOUT)*100%

AP3012 is a current mode PWM DC/DC converter with an internal oscillator with a fixed frequency. Its peripheral circuit is simple, with strong driving capability and high efficiency. The switching current of AP3012 reaches 500mA; when the input voltage is 5V and the load is 9’LED backliht, the output efficiency reaches 86%;

AP3012 itself has low cost, small size (SOT23-5), and small PCB area;

AP3012 only needs 6 components outside. Due to its up to 1.5MHz oscillation frequency, the peripheral inductance and capacitance are very small, and the cost of the entire circuit is very low;

AP3012 is flexible in application and can provide the BIAS voltage required by the display. It can drive the LED backlight screen in a constant voltage mode, and can also be used to generate the bias voltage of the LCD screen.

9. Application Note

In the arrangement of components, the input capacitor, oscillating inductance, voltage divider resistance, etc. should be as close as possible to AP3012, and the input and output lines should be as thick and short as possible. It is best to use Schottky diodes for output diodes. Choose capacitors with small ESR and small coil resistance of the inductor , To avoid high line loss and reduce its efficiency.

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