LTC1323CS View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LTC1323CS Datasheet PDF : 12 Pages
| |||
UU W U
APPLICATIO S I FOR ATIO
Driving an External Load from VEE
An external load may be connected between ground and
the VEE pin as shown in Figure 15. The LTC1323 VEE pin
will sink up to a maximum of 10mA while maintaining the
pin voltage between – 4.5V and – 5.5V. If an external load
is connected, the VEE bypass capacitor should be in-
creased to 4.7µF. Both LTC1323 and the external chip
should have separate VCC bypass capacitors but can
share the VEE capacitor.
EMI Filter
Most LocalTalk applications use an electromagnetic inter-
ference (EMI) filter consisting of a resistor-capacitor T
network between each driver and receiver and the connec-
tor. Unfortunately, the resistors significantly attenuate the
drivers output signals before they reach the cable. Because
+
1µF
VCC = 5V
24
12
LTC1323
13
21
+ 4.7µF
VCC
EXTERNAL
CHIP
GND
VEE
IVEE
–5.5V ≤ VEE ≤ –4.5V
IVEE ≤ 10mA
Figure 15
C1
LTC1323 • F15
LTC1323
the LTC1323 uses a single supply differential driver, the
resistor values should be reduced to 5Ω to 10Ω to guaran-
tee adequate voltage swing on the cable (Figure 16a). In
most applications, removing the resistors completely does
not cause an increase in EMI as long as a shielded connec-
tor and cable are used (Figure 16b). With the resistors
removed the only DC load is the primary resistance of the
LocalTalk transformer. This will increase the DC standby
current when the driver outputs are active, but does not
adversely affect the drivers because they can handle a
direct indefinite short circuits without damage. Trans-
former primary resistance should be above 15Ω to keep the
LTC1323 operating normally and prevent it from entering
thermal shutdown. For maximum swing and EMI immu-
nity, a ferrite bead and capacitor T network can be used
(Figure 16c).
5Ω TO 10Ω
5Ω TO 10Ω
100pF
FERRITE BEAD FERRITE BEAD
100pF
100pF
(a)
(b)
(c)
LTC1323 • F16
Figure 16. EMI Filters
TYPICAL APPLICATIONS N
Typical LocalTalk Connection
5V
1
0.33µF
2
DATA IN 3
TX ENABLE 4
SHDN 5
RX ENABLE 6
DATA OUT 7
1µF
16
15
CHARGE PUMP 14
13
LTC1323CS
12
TX
11
10
RX
9
8
0.33µF
100pF
100pF
100pF
100pF
1µF
LocalTalk
TRANSFORMER
120Ω
LTC1323 • TA02
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
Share Link: 