CPC5604 Datasheet, PDF (19/33 Pages) Clare, Inc. – Optical Data Access Arrangement I.C.

Figure 4 On-Hook DC Resistance Tip/Ring Setup
TIP
LITELINK^TM DAA Circuit
RING
CPC5604
A
+
100VDC
-
On-Hook Resistance
Figure 4 shows the test setup for on-hook DC resist-
ance. The battery is set to 100VDC and an ammeter is
placed in series with the battery connection. When the
DAA is in the on-hook state, the leakage current is
obtained and then the battery voltage is divided by this
current yielding the on-hook resistance. The LiteLink^TM
is guaranteed to have a leakage current < 10uA at 100V
which is equivalent to an on-hook resistance > 10MΩ
thus meeting regulatory approvals.
Current Limiting
The LiteLink^TM includes a current limiting feature that is
selectable via resistor R_ZDC (R16). The current limit
value is set by the equation:
10 ^1V 12
RZDC
For US/Canada/Japan the recommended value for
R_ZDC (R16) is 8Ω which yields a current limit value of
133mA. The current limiting feature is especially useful
in the case where the host system is inadvertently con-
nected to a digital PBX telephone port which usually has
a very high current limit value. The current limiting capa-
bility will prevent damage to the LiteLink^TM in this sce-
nario.
CTR-21 Compliance
CTR-21 is the standard for connection of data commu-
nications equipment to the European telephone net-
work. The maximum current limit requirement in
CTR-21 (Section 4.7.1) is 60mA and can be selected by
the following equation:
1V
ILM =
+ 8mA
RZDC
Clare recommends current limit be set to 53mA using an
R_ZDC value of 22Ω. Since V_DD is regulated to +3.5V,
excess power is dissipated in the external MOSFET
package. Since the maximum off-hook line voltage and
current in CTR-21 is 40V and 53mA respectively, the
maximum power dissipated by the MOSFET is approxi-
mately 2.1W.
AC Characteristics
In a similar manner to the DC characteristics, AC termi-
nation impedance is set via R_ZNT (R18). For all applica-
tions, a 604W resistor for R_ZNT (R18) is required to
reflect 600W to the CO.
XXX
www.clare.com
19