2-64

MH88520-1

Preliminary Information

Figure 2 - Pin Connections

Pin Description

Pin #

Name

Description

1TIP

Tip Lead. Connects to the “Tip” lead (A-wire) of the telephone line.

2IC

Internal Connection. Leave open circuit.

3

RING

Ring Lead. Connects to the “Ring” lead (B-wire) of the telephone line.

4RF1

Ring Feed 1. Connect to the Ring Relay contact. See Figure 5.

5IC

Internal Connection. Leave open circuit.

6RF2

Ring Feed 2. Connect to normally closed contact of Ring Relay. See Figure 5.

7IC

Internal Connection. Leave open circuit.

Negative Power Supply Voltage. Normally -5V.

9LED

LED Drive (Output). Drives an LED directly. A logic low indicates an off-hook condition.

10

SHK

Switch Hook Detect (Output). A logic low indicates an off-hook and dial pulsing

condition. Open collector output with 10k

Ω internal pull up to V

11

THRESH ADJ

Allows adjustment of SHK detection threshold as shown in Figure 6.

12

Positive Power Supply Voltage. Normally +5V. This provides current for both internal

circuitry as well as the loop.

13

AGND

Analog Ground. Supply and Battery Ground.

14

Battery Supply Voltage. Normally -24V. This provides current to the loop.

15

MUTE

MUTE (Input). A logic low will mute signals coming from Tip-Ring to the JUNC pin.

16

JUNC

JUNCTOR. Ground (AGND) referenced transmit and receive speech path.

17

RRD

Ring Relay Drive (Output). Connects to the ring relay coil. A logic low activates the

relay.

18

RGND

Relay Ground. Return path for relay supply voltage. Normally connected to AGND.

19

RRC

Ring Relay Control (Input). A logic high activates the Ring Relay Drive (RRD) outputs.

20

VRLY

Relay Positive Supply voltage. Normally +5V. Connects to the relay coil and the relay

supply voltage. An internal clamp diode from VRLY to GRND is provided.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

TIP

IC

RING

IC

RF2

IC

VEE

LED

SHK

THRESH ADJ

VDD

AGND

VBAT

MUTE

JUNC

RRD

RGND

RRC

VRLY

RF1