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參數(shù)資料
| 型號： | AN1500A |
| 廠商： | SAMES |
| 英文描述： | SINGLE CHIP TELEPHONE DEMO BOARD |
| 中文描述： | 單芯片電話演示板 |
| 文件頁數(shù)： | 22/27頁 |
| 文件大?。?/td> | 623K |
| 代理商： | AN1500A |
第1頁第2頁第3頁第4頁第5頁第6頁第7頁第8頁第9頁第10頁第11頁第12頁第13頁第14頁第15頁第16頁第17頁第18頁第19頁第20頁第21頁當前第22頁第23頁第24頁第25頁第26頁第27頁
AN1500A
sames
22/27
As a common rule, V
SS
ground planes should be as large as possible. “Bottlenecks” and long distances in the
ground path should be avoided.
Additionally, long distances between LI (#27) and the Emitter of the shunt transistor (Q3) should be avoided.
Therefore, Q3 should be placed near the IC pins :
collector = pin #26 =Vss,
base
= pin #25 = CS,
emitter
= pin #27 = LI.
21.3 EMC blocking parts:
Connections for blocking components, preferably ceramic capacitors (far less cost than coils) should be already
considered in the layout design. These capacitors should be connected as close to the IC (or line/handset
connector) pins as possible with a low-ohmic connection to V
SS
. SMD caps have best performance for EMC
blocking because of short leads and they can be placed directly underneath the IC at the solder junction.
f the use of SMD components is not possible, leaded ceramic capacitors can be connected at top PCB side as
shown in the demo board’s layout. Refer to EC1..EC7 on both schematic and layout.
The actual number of required EMC blocking components in the customer’s design cannot be predicted, since
EMC performance is influenced by many other factors, like telephone assembly, wire lengths etc.
21.4 Blocking of AGND:
For SA2532K EMC designs, it is very effective to block the AGND-pin (#5) with an inductor of
≈
150nH or
higher. This small inductance can be installed without extra cost by a printed coil with
≈
8..10mm diameter and
≥
5 turns (see PCB layout).
How to calculate the inductance of a printed spiral coil:
where:
n = number of turns
d
o
= outer diameter in cm
d
i
= inner diameter in cm
Example:
The printed coil used in the DB1500I layout has the following dimensions
(see Fig.12):
d
o
= 8.2 mm
[
d
i
= 2.6 mm
n = 5.5
Fig. 10:printed coil on DB1500I
PCB for EMC protection
Note: Instead of a printed coil, a helical air-coil (7mm diameter, 7..9mm length, 5..7 turns) made by a piece of
copper wire may also be used.
[
]
(
d
d
)
L
n
d
d
d
d
nH
o
i
o
i
o
i
≈
+
+
1075
.
1 .
2
]
.
.
)
L
nH
nH
≈
=
1075 55 082 026
1 272082 .
082 026
146
.
.
.
.
.
.
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