LTC1323
APPLICATIO S I FOR ATIO
Driving an External Load from V
EE
An external load may be connected between ground and
the V
EE
pin as shown in Figure 15. The LTC1323 V
EE
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 V
EE
bypass capacitor should be in-
creased to 4.7µF. Both LTC1323 and the external chip
should have separate V
CC
bypass capacitors but can
share the V
EE
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
V
CC
= 5V
+
1µF
24
12
LTC1323
13
V
CC
EXTERNAL
CHIP
GND
V
EE
I
VEE
4.7µF
–5.5V
≤
V
EE
≤
–4.5V
I
VEE
≤
10mA
21
LTC1323 • F15
Figure 15
TYPICAL APPLICATIONS
N
Typical LocalTalk Connection
5V
0.33µF
LTC1323CS
DATA IN
TX ENABLE
SHDN
RX ENABLE
DATA OUT
3
4
5
6
7
RX
12
TX
100pF
11
100pF
10
9
100pF
100pF
LTC1323 • TA02
8
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.
+
U
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
100pF
FERRITE BEAD
FERRITE BEAD
100pF
W
U
U U
C1
(a)
(b)
(c)
LTC1323 • F16
Figure 16. EMI Filters
+
+
1µF
16
1
2
CHARGE PUMP
15
14
13
0.33µF
1µF
LocalTalk
TRANSFORMER
120Ω
11
LINER [ LINEAR TECHNOLOGY ]
