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参数资料
| 型号： | LA8638NV |
| 元件分类： | 模拟运算功能 |
| 英文描述： | COMPANDER, PDSO30 |
| 封装： | SSOP-30 |
| 文件页数： | 14/16页 |
| 文件大小： | 107K |
| 代理商： | LA8638NV |
7. Protective Diodes Preventing Static Breakdown
The control pins and data output pins have had their upper protective diodes removed so as to permit direct
connection to a microcomputer.
No protective diodes:
VCC (pin 15), GND (pins 1 and 12)
Lower protective diodes only:
Pins 16 to 20, 22
Both upper and lower protective diodes: All other pins
8. Preemphasis and Deemphasis
This chip provides preemphasis in the microphone amplifier and deemphasis in the BTL amplifier's input stage. The
amount depends on the CR time constants for the filters on the corresponding pins—the primary high pass filter on
the microphone amplifier's positive (pin 28) or negative (pin 27) input for preemphasis and the primary low pass filter
between pins 10 and 11 for deemphasis.
9. Full-Wave Rectifier Smoothing Capacitors
The external capacitors on pins 8 and 25 are for the full-wave rectifiers for the expander and compressor. They not
only smooth the output but also determine the time constant for the transient characteristics. This time constant is the
product of the capacitance and 15 k
, the input resistance of the full-wave rectifier. Although there is a tendency to
lower the time constant for the expander to reduce noise at the ends of words, the designer must keep in mind that
such cuts reduce the amount of smoothing and thus raise the risk of distortion.
10. Compressor's Summing Amplifier
Achieving a DC gain of 1 and an AC gain of infinity from the compressor's summing amplifier requires suppressing
AC feedback with the capacitor on pin 3. The cutoff frequency is determined by the product of its capacitance and the
internal resistance of 22.5 k
.
11. Standby Function
The chip's standby function does not produce a total shutdown of all circuits. It disables the audio signal processing
block, but leaves the waveform shaper block for the receiving signal operating. For this reason, it is not possible to
connect the battery directly to the power supply pin (pin 15). There must be an intervening transistor switch for an
intermittent power supply.
12. Control Modes
No. 6627-7/16
LA8638NV
Pin 17
Pin 18
SUB-CNT1
SUB-CNT2
Mode
OPEN/HIGH
Standby
OPEN/HIGH
LOW
Receiver muted
LOW
OPEN/HIGH
Normal receiver output levels
LOW
Low receiver output levels
Pin Number
Pin Name
OPEN/HIGH
LOW
Pin 19
BTL-CNT
BTL amplifier disabled
BTL amplifier enabled
Pin 20
TX-MUTE
Transmitter muted
Transmitter enabled
Pin 22
TX-LVL-CNT
Normal transmitter output levels
High transmitter output levels
Note: The standby mode overrides all other mode settings.
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