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AP3029 Datasheet(PDF) 10 Page - BCD Semiconductor Manufacturing Limited |
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AP3029 Datasheet(HTML) 10 Page - BCD Semiconductor Manufacturing Limited |
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10 / 16 page  10 Oct. 2009 Rev. 1. 8 BCD Semiconductor Manufacturing Limited Data Sheet WHITE LED STEP-UP CONVERTER AP3029 Application Information Operation The AP3029 is a boost DC-DC converter which uses a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the Figure 3. At the start of each oscillator cycle, the SR latch is set and switch Q1 turns on. The switch current will increase linearly. The voltage on sense resistor is proportional to the switch current. The output of the current sense amplifier is added to a stabilizing ramp and the result is fed into the non-inversion input of the PWM comparator A2. When this voltage exceeds the output voltage level of the error amplifier A1, the SR latch is reset and the switch is turned off. It is clear that the voltage level at inversion input of A2 sets the peak current level to keep the output in regulation. This voltage level is the output signal of error amplifier A1, and is the amplified signal of the voltage difference between feedback voltage and reference voltage of 200mV. So, a constant output current can be provided by this operation mode. Figure 18. Typical Application circuit to Decide R1 LED Current Control Refer to Figure 18, the LED current is controlled by the feedback resistor R1. LEDs' current accuracy is determined by the regulator's feedback threshold accuracy and is independent of the LED's forward voltage variation. So the precise resistors are preferred. The resistance of R1 is in inverse proportion to the LED current since the feedback reference is fixed at 200mV. The relation for R1 and LED current can be expressed as below: Over Voltage Protection The AP3029 has an internal open-circuit protection circuit. When the LEDs are disconnected from circuit or fail open, the output voltage is clamped. The AP3029 will switch at a low frequency, and minimize input current. Soft Start The AP3029 has an internal soft start circuit to limit the inrush current during startup. The time of startup is controlled by internal soft start capacitor. Please refer to Figure 19. Figure 19. Soft Start Waveform VIN=3.6V, 5 LEDs, ILED=20mA Dimming Control Two typical types of dimming control circuit are present as below. First, controlling CTRL Pin voltage to change operation state is a good choice. Second, changing the feedback voltage to get appropriate duty and luminous intensity is also useful. (1). Adding a Control Signal to CTRL Pin There are three methods to control CTRL pin signal First, adding a PWM Signal to CTRL pin directly. The AP3029 is turned on or off by the PWM signal when it is applied on the CTRL pin. The typical frequency of LED I mV R 200 1 = IIN 100mA/div VOUT 5V/div VCTRL 2V/div Time 100 µs/div L1 C1 C2 R1 V IN SW V OUT FB GND CTRL AP3029 Control Signal V IN ≥ 3V VFB 100mV/div |
Similar Part No. - AP3029_09 |
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Similar Description - AP3029_09 |
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