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product without notice.

Publication# 21776

Rev: B Amendment: /0

Issue Date: July 1998

PRELIMINARY

Am79R70

Ringing Subscriber Line Interface Circuit

DISTINCTIVE CHARACTERISTICS

s Ideal for ISDN-TA and set top applications

s On-chip ringing with on-chip ring-trip detector

s Low standby state power

s Battery operation:

s On-chip battery switching and feed selection

s On-hook transmission

s Polarity reversal option

s Programmable constant-current feed

s Programmable Open Circuit voltage

s Programmable loop-detect threshold

s Current gain = 1000

s Two-wire impedance set by single component

s Ground-key detector

s Tip Open state for ground-start lines

(no external –5 V power supply required)

s Two on-chip relay drivers and snubber circuits

BLOCK DIAGRAM

E1

D2

D1

Two-Wire

Interface

HPA

HPB

Input Decoder

and Control

Relay

Driver

Ring-Trip

Detector

Power-Feed

Controller

RTRIP1

RTRIP2

BGND

VCC VNEG

RD

RDC

AGND/DGND

VBAT2

A(TIP)

B(RING)

RYOUT1

RDCR

C1

Switch

Driver

VBAT1

RSGL

Ground-Key

Detector

Off-Hook

Detector

Relay

Driver

RYOUT2

C2

C3

RSGH

B2EN

RSN

VTX

Signal

Transmission

RINGIN

RYE

DET