［AP2152］

MS1348-E-00

8

2012/05

OPERATION

1) Operation Outline

The AP2152 is composed of a current mode DC/DC boost convertor, 3 LED constant current source

channels, an LDO, and several protection circuits. It can drive a single LED line to three LED lines

connected together with a common anode. (Any unused channel should be left open)

This current mode DC/DC boost convertor has a built-in a power MOSFET, and the switching

frequency is determined by an external resistor or an external clock signal. The LED anode voltage is

optimized by monitoring each channel’s voltage and the channel voltage that has the highest forward

voltage is chosen. This voltage is used to control the DC/DC boost convertor’s output voltage . constant

current circuits for driving the LEDs are set by an external resistor, and PWM dimming is possible by

applying a PWM signal to the PWM pin. The latch-off time for the protection circuits, such over current

protection, channel short protection, and thermal protection can be set. There is also a PGOOD pin to

output the latch-off status.

The AP2152 flowchart at startup is shown in Figure 5.

When all CH pins are used, applying a PWM signal begins the DC/DC boost convertor operation. The

LED anode voltage rises, and if the LED current of all the CH reaches 1/10 of the set current, the

soft-start circuit is activated and the LED current gradually increases in approximately 1ms, and LEDs

are lit.

If there are any unused CH pins, the LED open detection circuit is activated at the beginning of the

DC/DC boost converter operation as soon as the PWM signal is applied. When the LED anode voltage

reaches the OVP preset value, the OVP state is detected. If a CH pin has not reached 1/10 of the LED set

current, an open state is recognized, and the LED constant current circuit will cease. For CH pins

connected to LEDs, the LED current reaches 1/10 of the set current, the normal connection is

recognized, and the LEDs are lit after the soft-start operation.

Figure 5. Flowchart at startup

Apply power

Apply PWM

Reference Voltage→ ON.

VDC →ON.

Power on

Reset.

Boost circuit ON.

Constant current circuit

(1/10 of the set current)

ON.

1/10 of the set

current flows to all

3 CH constant

current circuits.

Vout reaches

the OVP voltage.

Exclude open

CH from DC/DC

control.

Operate LED

current soft start

1ms

Normal

operation

300µs delay

Delay time 30µs

All CH pin are used(3CHs).

1 or 2CHs is/are used.

When a current is not

flowed on the constant

current circuit in the CH.

Initial determination mode

Boost circuit/constant

current circuit operation

continues regardless the

PWM signal level

(high/low).

Tsw×1920