AP3031KTR-G1 Просмотр технического описания (PDF) - BCD Semiconductor

Номер в каталоге

Компоненты Описание

производитель

AP3031KTR-G1

WHITE LED STEP-UP CONVERTER

BCD Semiconductor 

Data Sheet

WHITE LED STEP-UP CONVERTER

AP3031

Application Information

Operation

The AP3031 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 Figure 3 and

Figure 24.

At the start of each oscillator cycle, 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 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.

LED Current Control

Refer to Figure 24, the LED current is controlled by the

feedback resistor RISET. LEDs' current accuracy is

determined by the feedback voltage and resistor RISET,

so the precise resistors are preferred. The resistance of

RISET is in inverse proportion to the LED current since

the feedback reference is fixed at 200mV. The relation

for RISET and LED current (ILED)can be expressed as

below:

R ISET

=

200mV

I LED

Over Voltage Protection

The AP3031 has an internal open load protection

circuit. When the LEDs are disconnected from circuit

or fail open, the output voltage is clamped at about

17V. The AP3031 will switch at a low frequency, and

minimize current to avoid input voltage drop.

Soft Start

The AP3031 has an internal soft start circuit to limit

the inrush current during startup. If logic low time on

CTRL pin is more than about 0.7ms and then enable

the IC, the AP3031 will start smoothly to protect the

supplier. The time of startup is controlled by internal

soft-start capacitor. Details please refer to Figure 18.

VCTRL

5V/div

VSW

5V/div

>0.7ms

IL

500mA/div

VOUT

10V/div

Time 80µs/div

Figure 18. Soft-start Waveform

× VIN=5V, 3 13 LEDs, ILED=260mA

Standby and Dimming

To avoid audio noise and achieve high frequency dim-

ming, AP3031 is equipped with standby function. If

logic low time on CTRL pin is less than about 0.7ms

and then enable the IC, the AP3031 will hold on

standby mode and start directly to achieve high fre-

quency dimming. Details please refer to Figure 19.

VCTRL

5V/div

VSW

5V/div

<0.7ms

IL

500mA/div

VOUT

10V/div

Time 80µs/div

Figure 19. Standby Waveform

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,

Apr. 2009 Rev. 1. 3

BCD Semiconductor Manufacturing Limited

10

Share Link: