AP3152

120mA HIGH EFFICIENCY WHITE LED DRIVER

AP3152 Rev. 3

10 of 13

FEBRUARY 2009

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Functional Description

(Continued)

Disabled Current Sinks

Unused current channels must be disabled by connecting the

disabled channel.

Soft-Start and Soft-Stop

Soft-start and Soft-stop function are incorporated to prevent

excessive inrush current during power-up, mode switching,

power-down, transition out of stand-by mode.

Short-Circuit Protection

Short-circuit protection function is incorporated to prevent

excessive load current when either flying cap terminals or output

pin electrically tied to a very low voltage or ground.

Over-Voltage Protection

Over-voltage protection function is incorporated to limit the

output voltage under a safe value to avoid on-chip device

breakdown.

Under-Voltage Lockout

Under-voltage lockout feature disables the device when the

input voltage drops below UVLO threshold.

Thermal Shutdown

will be disabled and enter stand-by mode. The operation will be

resumed whenever the die cools off sufficiently.

Switching Frequency

By default, AP3152 is working at 1.2Mhz switching frequency. It

can also work at 0.6MHz or 1.8MHz switching frequency set

through SDI. User can choose the appropriate switching

frequency with consideration of noise immunity, input/output

voltage ripple requirement, and capacitor selection etc.

Up Spread Spectrum Control

When this feature is enabled through SDI, the switching

frequency periodically varies between 100% and 110% of

nominal frequency.

It flattens the peak energy on nominal

frequency over a range of frequency band so that EMI effect is

significantly reduced.

PWM Dimming Control

The AP3152 provides flexible dimming control with either

16-level SDI protocol control or PWM dimming control through

SDI pin. When PWM dimming control is enabled, the sink

current is adjusted by the duty cycle of the signal applied on SDI

pin.

Serial Digital Interface Continued

SDI Command Timing

For an SDI command to be successfully received by the AP3152, all SDI timing specifications should be satisfied. When no command is

being sent the SDI pin should be held high. If the SDI pin goes low and stays low for a time length of between TSLO(min) and TSLO(max)

and then goes high and stays high for between TSHI(min) and TSHI(max), one falling edge is registered by the AP3152. The total

number of falling edges registered before the SDI pin is held high for longer than the maximum separation time TSEP(max) identifies the

command that has been received by the AP3152. The next series of falling edges before another separation time TSEP represents the

next command. In other words, the AP3152 counts the number of consecutive falling edges on the SDI pin and a different number

represents a different command.

Each command is executed after it is successfully received. If at any time the SDI pin is held low for longer than the maximum chip

disable time TOFF(max), the AP3152 gets disabled and enters the shutdown mode. Setting the SDI pin high again will re-enable the

AP3152 and bring it out of the shutdown mode. Exiting from the shutdown mode, the AP3152 will retain all latest configuration settings

and return to the same state as before it was disabled.

The AP3152 enters the SDI mode by default when it is first powered up. The first SDI command 63 (63 falling edges) will put the AP3152

into the PWM mode, where a high level on the SDI pin turns the LEDs on, a low level turns the LEDs off and the duty cycle determines

the average LED brightness. The next SDI command 63 will put the AP3152 back into the SDI mode. It should be pointed out that the

PWM mode is for dimming control only and configuration settings have to be done in the SDI mode.

Channel Configuration Example

The following timing diagram is a dimming control example. In this example, the first command (command 10) selects Channel 2 as the

configuration target and the second command (command 2) sets the Channel 2 current level to one step lower while the other channels

remain unchanged.