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参数资料
| 型号： | TDA7421N |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 接收器 |
| 英文描述： | AM/FM, AUDIO SINGLE CHIP RECEIVER, PQFP64 |
| 封装： | TQFP-64 |
| 文件页数： | 15/47页 |
| 文件大小： | 374K |
| 代理商： | TDA7421N |
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Function description
TDA7421N
4.5.2
Charge pump current generator
This stage generates signed pulses of current. The phase error signal decides the duration
and polarity of those pulses.The current absolute values are programmable by A0, A1, A2
registers for high current and B0, B1 registers for low current.
4.5.3
Low noise CMOS op-amp
An internal voltage divider at pin VREF connects the positive input of the low noise Op-
Amp.The charge pump output connects the negative input. This internal amplifier in
cooperation with external components can provide an active filter. The negative input is
switchable to three input pins (LPIN 1, LPIN 2 and LPIN 3), to increase the flexibility in
application.This feature allows two separate active filters for different applications.A logical
"1" in the LPIN 1/2 register activates pin LPIN 1, otherwise pin LPIN 2 is active. While the
high current mode is activated LPIN 3 is switched on.
4.5.4
Inlock detector
The charge pump is switched in low current mode as the truth table and the related figure
shows.
The charge pump is forced in low current mode when a phase difference of 10-40 s is
reached.
A phase difference larger than the programmed values will switch the charge pump
immediately in the high current mode.
Few programmable delays are available for inlock detection.
4.6
IF counter system for AM/FM
The IF counter mode is controlled by IFCM register:
Table 9.
Truth table
Curr. high
Lock ENA
Lock (by inlock
detector)
Charge pump current
0
X
low current
1
low current
1
0
high current
1
0
1
high current
1
0
high current
Table 10.
IF counter mode
IFCM1
IFCM0
Function
00
Not used
0
1
FM mode
1
0
AM mode
11
Not used
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