HC55151 datasheet(19/35 Pages) INTERSIL

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4-19

Digital Logic Inputs

Table 1 is the logic truth table for the 3V to 5V logic input

pins. A combination of the control pins C3, C2 and C1 select

1 of the possible 6 operating states. The 8th state listed is

Thermal Shutdown. Thermal Shutdown protection is invoked

if a fault condition on the tip or ring causes the junction

temperature of the die to exceed 175oC. A description of

each operating state and the control logic follows:

Open Circuit State (C3 = 0, C2 = 0, C1 = 0)

In this state, the tip and ring outputs are in a high impedance

condition (>1M

Ω). No supervisory functions are available

and SHD and GKD outputs are at a TTL high level.

4-wire loopback testing can be performed in this state. With

the PTG pin ﬂoating, the signal on the VTX output is 180

o out

of phase and approximately 2 times the VRX input signal. If

the PTG pin is grounded, then the amplitude will be

approximately the same as its input and 180o out of phase.

Ringing State (C3 = 0, C2 = 0, C1 = 1)

In this state, the output of the ring relay driver pin (RRLY)

goes low (energizing the ring relay to connect the ringing

signal to the phone) if either of the following two conditions

are satisﬁed:

(1) The RSYNC_REV pin is grounded through a resistor -

This connection enables the RRLY pin to go low the instant

the ringing state is invoked, without any regard for the ringing

voltage (90VRMS -120VRMS) across the relay contacts. The

resistor (34.8k

Ω to 70kΩ) is required to limit the current into

the RSYNC_REV pin.

(2) A ring sync pulse is applied to the RSYNC_REV pin -

This connection enables the RRLY pin to go low at the

command of a ring sync pulse. A ring sync pulse should go

low at zero voltage crossing of the ring signal. This pulse

should have a rise and fall time <400

µs and a minimum

pulse width of 2ms.

Zero ring current detection is performed automatically

inside the SLIC. This feature de-energizes the ring relay

slightly before zero current occurs to partially compensate

for the delay in the opening of the relay.

The SHD output will go low when the subscriber goes off

hook. Once SHD is activated, an internal latch will prohibit

the re-ringing of the line until the ringing code is removed

and then reapplied.

The state prior to ringing the phone, can not be the Reverse

Active State. In the reverse active state the polarity of the

voltage on the CRT_REV_LVM capacitor, will make it appear

as if the subscriber is off hook. This subsequently will

activate an internal latch prohibiting the ringing of the line.

TABLE 1. DETECTOR STATES

STATE

SLIC OPERATING STATE

ACTIVE DETECTOR

OUTPUT

SHD

GKD_ LVM

Open Circuit State

4 wire loopback test capability

HIGH

Ringing State

(Previous State cannot be Reverse

Active State)

Ring Trip Detector

HIGH

Forward Active State

Loop Current Detector

Ground Key Detector

Test Active State

Requires previous state to be in the

Forward Active state to determine the

On hook or Off hook status of the line.

On Hook Loopback Detector

LOW

Ground Key Detector

HIGH

Off Hook Loop Current Detector

LOW

Line Voltage Detector

Tip Open - Ground Start State

Ground Key Detector

Reserved

N/A

Reverse Active State

Loop Current Detector

Ground Key Detector

Test Reversal Active State

Requires previous state to be in the

Reverse Active state to determine the

On hook or Off hook status of the line.

On Hook Loop Current Detector

HIGH

Off Hook Loop Current Detector

LOW

Line Voltage Detector

Thermal Shutdown

LOW

HC55120, HC55121, HC55130, HC55131, HC55140, HC55141, HC55142, HC55143, HC55150, HC55151

HC55151 Datasheet(PDF) 19 Page - Intersil Corporation

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