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PDF LM4970 Data sheet ( Hoja de datos )
| Número de pieza | LM4970 | |
| Descripción | Audio Synchronized Color LED Driver | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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February 2005
LM4970
Audio Synchronized Color LED Driver
General Description
The LM4970 is a LED driver with an audio synchronization
mode that virtually eliminates the need for real time software
processing for LED lighting effects. The LM4970 includes
three individual PWM color LED drivers that provide up to
42mA of current drive for each PWM LED output.
The LM4970 features an audio synchronization mode where
the audio input signal that is mixed in from three audio inputs
is filtered into three frequency bands, with each frequency
band assigned to a specific PWM LED driver.
The PWM LED drivers can also be directly programmed
through an I2C compatible interface for applications where
user defined LED pattern, color, and intensity programmabil-
ity is a priority.
The LM4970 also features an audio input gain control which
allows the user to increase the gain if the audio input signal
does not create a bright enough effect on the LEDs. The
LM4970 is a feature rich LED driver that is available in a
space saving 14 pin non-pullback LLP package.
Key Specifications
j LED Drive Current per channel
VDD = 5V
j Shutdown Current, VDD = 5V
42mA (2X setting)
1.5µA (typ)
Features
n Audio synchronized color LED driver
n User defined LED pattern, color, and intensity capability
n Programmable:
LED Drive current
PWM frequency
High pass filter frequency select
Audio input signal gain
n Eliminates external LED current limiting resistors
n I2C compatible interface
n Ultra low shutdown current
Applications
n Cell Phones
n Portable MP3, CD, DVD, AAC players
n PDA’s
Block Diagram
FIGURE 1. Block Diagram
20121201
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2005 National Semiconductor Corporation DS201212
www.national.com
1 page  
External Components Description
Components
1. Ci
2. CS
3. Cfilt
Functional Description
This is the input coupling capacitor. It blocks the DC voltage and couples the input signal to the
amplifier’s input terminals. CIN also creates a highpass filter with an internal 20kΩ resistor at fc =
1/(2π.20000.Ci).
This is the supply bypass capacitor. It filters the supply voltage applied to the VDD pin and helps
reduce the noise at the VDD pin.
This capacitor creates a low pass filter with an internal 4kΩ resistor at fc = 1/(2π*4000*Cfilt). This pole
set at fc determines the high cutoff frequency for the low band PWM color LED driver output, LED1.
Typical Performance Characteristics (Note 11)
Audio Sync LED Frequency Response
(Left - lowband, Mid - midband, Right - highband)
(Cfilt = 0.047µF, HPF = 3.5kHz setting)
Audio Sync LED Frequency Response
(Left - lowband, Mid - midband, Right - highband)
(Cfilt = 0.068µF, HPF = 3.5kHz setting)
20121265
Audio Sync LED Frequency Response
(Left - lowband, Mid - midband, Right - highband)
(Cfilt = 0.1µF, HPF = 3.5kHz setting)
20121266
Audio Sync LED Frequency Response
(Left - lowband, Mid - midband, Right - highband)
(Cfilt = 0.22µF, HPF = 3.5kHz setting)
20121267
5
20121268
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5 Page 
Application Information (Continued)
Data Bit Bit Name
GSO
MGAIN0
GS1
MGAIN1
GS2
MGAIN2
GS3
SGAIN0
GS4
SGAIN1
GS5
SGAIN2
Default
Value
0
1
0
0
1
0
TABLE 7. Gain Select Register
Condition
Function
0 Programs the gain response of the midband audio synchronized filter
which drives the LED2 PWM color LED driver for the midband audio
1 frequencies. Gain is set as follows:
0 MGAIN<2:0>
1
Midband Filter Gain
0 000
minimum
001 low
010
1
011
medium
high
100 maximum
0 Programs the audio gain of the input summing amplifier. Gain is set
as follows:
1 SGAIN<2:0>
Input Signal Gain
0 000
–11dB
1 001
–6.5dB
010
0
011
0dB
3.5dB
100 6dB
1 101
10dB
110 12dB
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