AP3019 查看數據表（PDF） - BCD Semiconductor

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AP3019

WHITE LED STEP-UP CONVERTER

BCD Semiconductor 

Preliminary Datasheet

WHITE LED STEP-UP CONVERTER

Application Information

Operation

The AP3019 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.

R1

=

200mV

I LED

AP3019

Over Voltage Protection

The AP3019 has an internal open-circuit protection

circuit. When the LEDs are disconnected from circuit

or fail open, the output voltage is clamped at 27V. The

AP3019 will switch at a low frequency, and minimize

input current.

Soft Start

The AP3019 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 20.

It is clear that the voltage level at non-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.

VIN ≥ 3V

L1

IIN

100mA/div

VOUT

10V/div

VCTRL

2V/div

VIN SW

VOUT

Control

AP3019

C2

Signal

CTRL

FB

GND

C1

R1

Time 100µs/div

Figure 20. Soft Start Waveform

VIN=3.6V, 4LEDS, ILED=20mA

Figure 19. Typical Application circuit to Decide R1

LED Current Control

Refer to Figure 19, 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:

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

AP3019 is turned on or off by the PWN signal when it

is applied on the CTRL pin. The typical frequency of

Apr. 2007 Rev. 1. 1

BCD Semiconductor Manufacturing Limited

10

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