ISL5585_04 Datasheet, PDF (19/24 Pages) Intersil Corporation – 3.3V Ringing SLIC Family for Voice Over Broadband (VOB)

ISL5585
When the forward loop back mode is initiated internal
switches connect a 600Ω load across the outputs of the Tip
and Ring amplifiers.
TIP
TIP AMP
RING
600Ω
RING AMP
FIGURE 13. FORWARD LOOP BACK INTERNAL TERMINATION
DC Verification
When the internal signal path is provided, DC current will
flow from Tip to Ring. The DC current will force DET low,
indicating the presence of loop current. In addition, the ALM
output will also go low. This does not indicate a thermal
alarm condition. Rather, proper logic operation is verified in
the event of a thermal shutdown. In addition to verifying
device functionality, toggling the logic outputs verifies the
interface to the system controller.
AC Verification
The entire AC loop of the device is active during the forward
loop back mode. Therefore a 4-wire to 4-wire level test
capability is provided. Depending on the transhybrid balance
implementation, test coverage is provided by a one or two
step process.
System architectures which cannot disable the transhybrid
function would require a two step process. The first step
would be to send a test tone to the device while on hook and
not in forward loop back mode. The return signal would be
the test level times the gain R_F/R_A of the transhybrid
amplifier. Since the device would not be terminated,
cancellation would not occur. The second step would be to
program the device to FLB and resend the test tone. The
return signal would be much lower in amplitude than the first
step, indicating the device was active and the internal
termination attenuated the return signal. System
architectures which disable the transhybrid function would
achieve test coverage with a signal step. Once the
transhybrid function is disable, program the device for FLB
and send the test tone. The return signal level is determined
by the 4-wire to 4-wire gain of the device.
Tip Open
Overview
The tip open mode (110) is intended for compatibility for PBX
type interfaces. Used during idle line conditions, the device
does not provide transmission. Loop supervision is provided
by either the switch hook detector (E0 = 1) or the ground key
detector (E0 = 0). The ground key detector will be used in
most applications. The device may be operated from either
high or low battery.
Functionality
During tip open operation, the Tip switch is disabled and the
Ring switch is enabled. The minimum Tip impedance is
30kΩ. The only active path through the device will be the
Ring switch.
In keeping with the MTU characteristics of the device, Ring
will not exceed -56V when operating from the high battery.
Though MTU does not apply to tip open, safety requirements
are satisfied.
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