AP3612 datasheet(13/18 Pages) BCDSEMI

13 / 18 page

Preliminary Datasheet

Boost Type LED Driver with 12-Channel Current Source

AP3612

Aug. 2012 Rev. 1. 1

BCD Semiconductor Manufacturing Limited

Application Information

1. Enable

The AP3612 is enabled when the voltage to EN is

greater than approximately 2.4V, disabled when lower

than 0.5V.

2. Frequency Selection

An external resistor RT, placed between RT pin and

GND, can be used to set the operating frequency. The

operating frequency ranges from 100kHz to 1MHz.

The high frequency operation optimizes the regulator

for the smallest-sized component application, while

low frequency operation can help to reduce switch

loss. The approximate operating frequency can be

expressed as below:

]

[

]

[

Ω

MHz

OSC

3. LED Current Setting

The maximum LED current per channel can be

adjusted up to 75mA via ISET pin. When ≥75mA

current is needed in application, two or more

channels can be paralleled to provide larger drive

current. Connect a resistor RISET between ISET pin

and GND to set the reference current ISET. The LED

current can be expressed as below:

]

[

400

]

[

Ω

ISET

LED

4. Dimming Control

Applying a PWM signal to DIM pin to adjust the

LED current, that means, the LED current of all

enabled channels can be adjusted at the same time

and the LED brightness can be adjusted from 1%×

ICHX_MAX to 100% × ICHX_MAX. During the “high

level” period of PWM signal, the LED is turned on

and 100% of the current flows through LED, while

during the “low level” period of the PWM signal, the

LED is turned off and almost no current flows

through the LED, thus changing the average current

through LED and finally adjusting LED brightness.

The external PWM signal frequency applied to PWM

pin is allowed to be 100Hz or higher.

5. Status Output

After IC is enabled, STATUS will output logic low if

any of the following conditions exists:

1) Any String is Open

2) LED Short Circuit Protection

3) Shut Down Under Abnormal Condition

4) Over Temperature Protection

5) Schottky Diode Short Protection

6) Over Voltage Protection

7) VOUT Short/Open Schottky Diode Protection

6. Over Voltage Protection

The AP3612 integrates an OVP circuit. The OVP pin

is connected to the center tap of voltage-divider (ROV1

and ROV2) that placed between high voltage output

and GND. If the voltage on OVP pin exceeds 2.0V,

which may results from open loop or excessive

output voltage, all the functions of AP3612 will be

disabled with output voltage falling. The OVP

hysteresis is 250mV. The formula of OVP can be

expressed as below:

OV2

OV1

OVP

2.0V

)

7. Over Current Protection

The AP3612 integrates an OCP circuit. The CS pin is

connected to the voltage-sensor (RCS) that placed

between the Drain of MOS and GND. If the voltage

on CS pin exceeds 0.54V, it is turned off immediately

and will not turn on until the next cycle begins.

8. LED Short-circuit Protection

The AP3612 integrates an LED Short-circuit

protection circuit. If the voltage at any of the

CH1-CH12

pins

exceeds

threshold

approximately 7.3V during normal operation, the

corresponding string is turned off and is latched off.

Toggle VIN and/or EN to reset the latch. LED short

detecting logic priority is lower than open LED and

OVP logic. The LED short detecting is triggered

when 0.1V<VLED_MIN under dimming on mode,

disabled when LED open occurs until output voltage

resumes to the regulated voltage.

AP3612 Datasheet(PDF) 13 Page - BCD Semiconductor Manufacturing Limited

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