AN1500A South African Micro-Electronic Systems, AN1500A Datasheet - Page 22

• Manufacturer Part Number: AN1500A
• Description: Single Chip Telephone Demo Board
• Manufacturer: South African Micro-Electronic Systems

As a common rule, V
Additionally, long distances between LI (#27) and the Emitter of the shunt transistor (Q3) should be avoided.
collector = pin #26 =Vss,
base
emitter
21.3 EMC blocking parts:
Connections for blocking components, preferably ceramic capacitors (far less cost than coils) should be already
If the use of SMD components is not possible, leaded ceramic capacitors can be connected at top PCB side as
The actual number of required EMC blocking components in the customer’s design cannot be predicted, since
21.4 Blocking of AGND:
How to calculate the inductance of a printed spiral coil:
Example:
The printed coil used in the DB1500I layout has the following dimensions
(see Fig.12):
d
d
n = 5.5
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.
o
i
22/27
= 8.2 mm
= 2.6 mm
ground path should be avoided.
Therefore, Q3 should be placed near the IC pins :
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
blocking because of short leads and they can be placed directly underneath the IC at the solder junction.
shown in the demo board’s layout. Refer to EC1..EC7 on both schematic and layout.
EMC performance is influenced by many other factors, like telephone assembly, wire lengths etc.
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
L
AN1500A
5 turns (see PCB layout).
nH
= pin #27 = LI.
10 75
1 2 72
.
.
= pin #25 = CS,
n d
2
SS
d
d
L
o
o
nH
o
ground planes should be as large as possible. “Bottlenecks” and long distances in the
d
d
d
i
i
i
10 75 5 5 0 82 0 26
1 2 72
.
sames
sames
sames
sames
.
.
2
0 82 0 26
0 82 0 26
.
.
where:
n = number of turns
d
d
.
o
i
= inner diameter in cm
= outer diameter in cm
.
.
.
146
nH
SS
. SMD caps have best performance for EMC
Fig. 10:printed coil on DB1500I
PCB for EMC protection