LP3950SL datasheet(16/31 Pages) NSC

16 / 31 page

Boost Converter Typical Performance Characteristics V

IN = 3.6V, VOUT = 5.0V if not

otherwise stated. (Continued)

Boost Line Regulation

Boost Load Transient Response, 50 mA to 100 mA

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20129323

RGB LED Pattern Generator

The LP3950 RGB outputs can be controlled either with audio

synchronization or with RGB pattern generator.

The pattern generator of LP3950 drives three independently

controlled LED outputs (for example, R1, G1 and B1). The

functionality is similar compared to RGB functionality of

LP3936 and LP3933.

The output of RGB pattern generator can be selected to

drive RGB1 (R1-G1-B1), RGB2 (R2-G2-B2) or RGB1 and

RGB2 (R1&R2 – G1&G2 – B1&B2) outputs.

Programmable Pattern Mode

User has control over the following parameters separately

for each LED:

• ON and OFF (start and stop time in blinking cycle)

• DUTY

(PWM brightness control)

• SLOPE

(dimming slope)

• ENABLE

(output enable control)

The main blinking cycle is controlled with three-bit CYCLE

control (0.25 / 0.5 / 1.0 / 2.0 / 4.0s).

RGB_START is the master control for the whole RGB func-

tion. The internal PWM and blinking control can be disabled

by setting the RGB_PWM control LOW. In this case the

individual enable controls can be used to switch outputs on

and off. PWM_EN input can be used for external hardware

PWM control.

In the normal PWM mode the R, G and B switches are

controlled in 3 phases (one phase per driver). During each

phase the peak current set by an external ballast resistor is

driven through the LED for the time defined by DUTY setting

(0 µs to 50 µs). As a time averaged current this means

0% to 33% of the peak current. The PWM period is 150 µs

and the pulse frequency is 6.67 kHz in normal mode.

In the FLASH mode all the outputs are controlled in one

phase and the PWM period is 50 µs. The time averaged

FLASH mode current is three times the normal mode current

at the same DUTY value.

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FIGURE 12. RGB PWM Operating Principle

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FIGURE 13. Normal Mode PWM Waveforms at Different

Duty Settings

LP3950SL Datasheet(PDF) 16 Page - National Semiconductor (TI)

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