4-16

Pin Descriptions

PLCC

SYMBOL

DESCRIPTION

1

TIP

TIP power amplifier output.

2

BGND

Battery Ground - To be connected to zero potential. All loop current and longitudinal current flow from this ground.

Internally separate from AGND but it is recommended that it is connected to the same potential as AGND.

3

VBL

Low battery supply connection.

4

VBH

High battery supply connection for the most negative battery.

5

SW+

Uncommitted switch positive terminal.

6

SW-

Uncommitted switch negative terminal.

7

SWC

Switch control input. This TTL compatible input controls the uncommitted switch, with a logic “0” enabling the switch and

logic “1” disabling the switch.

8

F2

Mode Control Input - MSB. F2-F0 for the TTL compatible parallel control interface for controlling the various modes of

operation of the device.

9

F1

Mode control input.

10

F0

Mode control input.

11

E0

Detector Output Selection Input. This TTL input controls the multiplexing of the SHD (E0 = 1) and GKD (E0 = 0)

comparator outputs to the DET output based upon the state at the F2-F0 pins (see the Device Operating Modes table

shown on page 2).

12

DET

Detector Output - This TTL output provides on-hook/off-hook status of the loop based upon the selected operating mode.

The detected output will either be switch hook, ground key or ring trip (see the Device Operating Modes table shown on

page 2).

13

ALM

Thermal Shutdown Alarm. This pin signals the internal die temperature has exceeded safe operating temperature

14

AGND

Analog ground reference. This pin should be externally connected to BGND.

15

BSEL

Selects between high and low battery, with a logic “1” selecting the high battery and logic “0” the low battery.

16

TL

Programming pin for the transient current limit feature, set by an external resistor to ground.

17

POL

External capacitor on this pin sets the polarity reversal time.

18

VRS

Ringing Signal Input - Analog input for driving 2-wire interface while in Ring Mode.

19

VRX

Analog Receive Voltage - 4-wire analog audio input voltage. AC couples to CODEC.

20

VTX

Transmit Output Voltage - Output of impedance matching amplifier, AC couples to CODEC.

21

VFB

Feedback voltage for impedance matching. This voltage is scaled to accomplish impedance matching.

22

-IN

Impedance matching amplifier summing node.

23

VCC

Positive voltage power supply, usually +5V.

24

CDC

25

RTD

Ring trip filter network.

26

ILIM

Loop Current Limit programming resistor.

27

RD

Switch hook detection threshold programming resistor.

28

RING

RING power amplifier output.

HC55185