2
Lucent Technologies Inc.
Data Sheet
February 1998
LH1465AB/AAE ISDN dc Termination IC
Functional Description
The LH1465 plays a dual role in the ISDN NT1: first, as
an electronic inductor for a dc termination with high ac
impedance; and second, as part of the dc signaling
system for line testing capability. The LH1465 meets or
exceeds all specifications for the ISDN NT1 dc termina-
tion as described by ANSI Standard T1.601-1991.
Use of the LH1465 requires only a few discrete compo-
nents. See Figure 11 for a typical NT1 application. The
LH1465 is current limited, but is not an overvoltage
surge protector. A crowbar-type surge protector limiting
the line voltage to less than 250 V is recommended to
protect the LH1465. The surge protector must with-
stand the requirements in Tables 4 and 5. One such
protector is the
Teccor
* Inc., P2000AA61
SIDACTOR
*.
The LH1465 has a polarity guard so that the device
gives the same characteristics whether the NT1 TIP or
RING terminal is connected to the battery voltage. TIP
and RING are connected directly to the LH1465AB
terminals 2 and 3 and to the LH1465AAE terminals 4
and 5.
The dc T to R I-V characteristics of the LH1465 are
shown in Figures 2 and 3. As battery voltage is applied
to the loop, the LH1465 conducts current only when the
voltage across the LH1465 exceeds about 35 V. With
35 V or more applied to the LH1465A, the device con-
ducts about 150
μ
A of current for about 20 ms and then
turns on and goes into the ON state. The LH1465 will
remain in the ON state for as long as the loop current
exceeds 0.5 mA.
The LH1465 has a turn-on and turn-off timing circuit
that ensures that the LH1465 will: a) not turn on if a
voltage above 43.5 V is applied for less than 3 ms; and
b) not turn off if the loop current is interrupted for less
than 3 ms.
Current for the LED of the optocoupler flows when the
current in the LH1465 is greater than 1 mA. However,
the LH1465 is guaranteed to turn on if a voltage above
43.5 V is applied for more than 50 ms, and turn off if
1 mA loop current is interrupted for more than 100 ms.
See Figures 6, 7, and 8 of this document or Table F1 in
Appendix F of ANSI Standard T1.601-1991.
Current for the LED is interrupted when loop current is
interrupted. The current in the ON state is determined
by the battery voltage and loop resistance. Should the
loop resistance be negligible and/or applied voltage
excessively large, the LH1465 will limit the loop current
to less than 60 mA. While in current limit, the LH1465
shunts the 2.2 k
, 4 W power resistor R2 across itself
to protect against excessive thermal heating.
In the event that fault voltages exceeding 100 V are
impressed upon TIP and RING, the LH1465 will shut
off and go into a standby mode where very little current
flows. When the fault voltage is removed, the LH1465
goes back into its normal ON-state operation.
Pin Descriptions
DIP SOG
1
Symbol
PR+
Name/Function
Protection resistor positive
side
Tip side of the loop
Ring side of the loop
Protection resistor negative
side
Common
Photodiode (LED input
current)
Current-limit resistor
Timing capacitor
No connection
No connection
No connection
No connection
1
2
3
4
4
5
8
T
R
PR–
5
6
9
COM
PD
12
7
8
13
16
2, 3
6, 7
10, 11
14, 15
RS
TC
NC
NC
NC
NC
*
Teccor
is a trademark and
SIDACTOR
is a registered trademark of Teccor, Inc.