0

-100

kHz

0

8.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

-10

-20

-30

-40

-50

-60

-70

-80

-90

BANDPASS

LOWPASS

HIPASS

0

-100

kHz

0

4.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-10

-20

-30

-40

-50

-60

-70

-80

-90

BANDPASS

LOWPASS

HIPASS

LP3950 AUDIO SYNCHRONIZATION

SYNC_MODE = 1

SYNC_MODE = 0

AMPLITUDE

SYNC.

FREQUENCY

SYNC.

MODE0

MODE1

MODE2

MODE0

MODE1

FASTEST

FAST

MEDIUM

SLOW

FASTEST

FAST

MEDIUM

SLOW

FASTEST

FAST

MEDIUM

SLOW

FASTEST

FAST

MEDIUM

SLOW

FASTEST

FAST

MEDIUM

SLOW

LP3950

www.ti.com

SNVS331C – NOVEMBER 2004 – REVISED APRIL 2013

Figure 27. LP3950 Audio Synchronization Functionality

MODE CONTROL IN THE FREQUENCY MODE

During the frequency mode (SYNC_MODE = 1) the user can select between two filter options by

MODE_CTRL[1:0] as shown below (Figure 29). User can select the filters based on the music type and light

effect requirements. Filter options: Left figure, wide frequency response; MODE_CTRL[1:0] is set to [00], [10] or

[11]. Right figure, narrow frequency response: MODE_CTRL[1:0] set to [01]. Signal passed through the lowpass

filter is used to control the duty cycle of red LEDs (R1 and/or R2 PWM outputs), the signal passed through the

bandpass filter is used to control green LEDs (G1 and/or G2 PWM outputs) and high pass signal controls blue

LEDs (B1 and/or B2 PWM outputs). Finally, the user can select the desired mapping speed by

SPEED_CTRL[1:0]. Of course, the user can connect any color LED to any output in his/her own application (i.e.

the red output does not need to drive a red LED). Maximum duty cycle is 100% as in the Flash mode (not 33%

as in the normal mode of the pattern generator, which is described in Table 3).

Figure 28. Cross-over Frequency

Figure 29. Cross-over Frequency

Left: Wide Frequency Response

Right: Narrow Frequency Response

MODE CONTROL IN THE AMPLITUDE MODE

During the amplitude synchronization mode (SYNC_MODE = 0) the user can select between three different

amplitude mappings by using MODE_CTRL[1:0] select. These three mapping options give different light

responses as shown in Figure 30. Again, the user can select the desired mapping speed by SPEED_CTRL[1:0].

Maximum duty cycle is 100%. If MODE_CTRL[1:0] = 11 and SYNC_MODE = 0, audio synchronization is

inactive.

Copyright © 2004–2013, Texas Instruments Incorporated

Submit Documentation Feedback

25

Product Folder Links: LP3950