Electronic Volume Controller IC PT2257 DESCRIPTION
The PT2257 is an electronic volume controller IC utilizing CMOS technology specially designed for the new generation of AV entertainment products. It has two (2) built-in channels making it ideally suitable for mono and stereo sound applications. The PT2257 provides an I2C control interface, an attenuation range of 0 to -79dB, low noise, and high channel separation. It is housed in an 8 pins, DIP or SOP package, The PT2257’s pin assignments and application circuit are optimized for easy PCB layout and cost saving advantages.
FEATURES
x CMOS technology
x Low power consumption
x Least external components
x Attenuation range: 0 to -79dB at 1dB/step
x Operating voltage: 3 to 9V
x Low Noise, S/N Ratio>100dB (A-weighting)
x Two channel output
x Available in 8 pins, DIP or SOP
APPLICATIONS
x AV surround audio equipment
x Car audio
x Mini compo
x Computer multi-media speaker
x Other audio equipment
PT2257 V1.4 - 1 - May, 2008
PT2257 V1.4 - 2 - May, 2008
Electronic Volume Controller IC PT2257
BLOCK DIAGRAM
L IN
L O UT
V DD
R IN
S DA
S CL
Vss
10dB /St ep
10dB /St ep
1dB /Ste p
1dB /Ste p
R ef
C ontrol unit R OU T
+-+
+--
PT2257 V1.4 - 3 - May, 2008
Electronic Volume Controller IC PT2257
PIN CONFIGURATION
PT2257
LIN LOUT VS S SDA
RIN ROUT VDD SCL
PIN DESCRIPTION
Pin Name
I/O
Description
Pin No. L IN  I
Left input channel
Connect a capacitor to audio source 1L OUT  O
Left output channel
Connect a capacitor to audio output
2
V SS  - Ground    3 SDA I I 2C data input    4 SCL I I 2C clock input    5
V DD  - Power supply
6 R OUT  O
Right output channel
Connect a capacitor to audio output 7R IN  I
Right input channel
Connect a capacitor to audio source
8
Electronic Volume Controller IC PT2257 FUNCTION DESCRIPTION
BUS INTERFACE
Data are transmitted to and from the microprocessor to the PT2257 via the SDA and SCL. The SDA an
d SCL make up the BUS Interface. It should be noted that the pull-up resistors must be connected to the positive supply voltage.
DATA VALIDITY
A data on the SDA Line is considered valid and stable only when the SCL Signal is in HIGH State. The HIGH and LOW States of the SDA Line can only change when the SCL signal is LOW. Please refer to the figure below.
D ATA
C L K
D a ta Lin e S ta b le, D a ta Va lid
D a ta C h a ng e Allo w e d
START AND STOP CONDITIONS
A Start Condition is activated when
1. The SCL is set to HIGH and
2. SDA shifts from HIGH to LOW State.
The Stop Condition is activated when
1. SCL is set to HIGH and
2. SDA shifts from LOW to HIGH State.
Please refer to the timing diagram below.
DATA
CLK
Start Stop
PT2257 V1.4 - 4 - May, 2008
Electronic Volume Controller IC PT2257 BYTE FORMAT
Every byte transmitted to the SDA Line consists of 8 bits. Each byte must be followed by an Acknowledge Bit. The MSB is transmitted first.electronic去掉ic是什么
ACKNOWLEDGE
During the Acknowledge Clock Pulse, the master (µP) puts a resistive HIGH level on the SDA Line. The peripheral (audio processor) that acknowledges has to pull-down (LOW) the SDA line during the Acknowledge Clock Pulse so that the SDA Line is in a Stable Low State during this Clock Pulse. Please refer to the diagram below.
SD A
SC L
Start MSB
Acknowledgment
from R eceiver 123789
4
The audio processor that has been addressed has to generate an Acknowledge after receiving each byte; otherwise, the SDA Line will remain at the High Level during the ninth (9th) Clock Pulse. In this case, the master transmitter can generate the STOP Information in order to abort the transfer. TRANSMISSION WITHOUT ACKNOWLEDGE
If you want to avoid the acknowledge detection of the audio processor, a simpler µP transmission may be used. Wait one clock and does not check the slave acknowledge of this same clock then send the new data. If you use this approach, there are greater chances of faulty operation as well as decrease in noise immunity.
PT2257 V1.4 - 5 - May, 2008

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