AM79R70 datasheet(11/20 Pages) AMD

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Table 2. User-Programmable Components

ZT is connected between the VTX and RSN pins. The fuse resistors are

RF, and Z2WIN is the desired 2-wire AC input impedance. When com-

puting ZT, the internal current amplifier pole and any external stray ca-

pacitance between VTX and RSN must be taken into account.

ZRX is connected from VRX to RSN. ZT is defined above, and G42L is the

desired receive gain.

RDC1, RDC2, and CDC form the network connected to the RDC pin.

ILOOP is the desired loop current in the constant-current region.

RDCR1, RDCR2, and CDCR form the network connected to the RDCR pin.

See Applications Circuit for these components.

CDCR sets the ringing time constant, which can be between 15 µs and

150 µs.

for high battery state

RD is the resistor connected from the RD pin to GND and RLTH is the

loop-resistance threshold between on-hook and off-hook detection. RD

should be greater than 56 k

Ω to guarantee detection will occur in the

Standby state. Choose the value of RD for high battery state; then use

the equation for RLTH to find where the threshold is for low battery.

Loop-Threshold Detect Equations

for high battery

This is the same equation as for RD in the preceding equation, except

solved for RLTH.

for low battery

For low battery, the detect threshold is slightly higher, which will avoid

oscillating between states.

RLTH standby < RLTH active VBAT1 < RLTH active VBAT2, which will guar-

antee no unstable states under all operating conditions. This equation

will show at what resistance the standby threshold will be; it is actually

a current threshold rather than a resistance threshold, which is shown

by the Vbat dependency.

500 Z

2WIN

–

()

42L

------------

1000

•

500 Z

()

--------------------------------------------------

•

DC 1

DC2

2500

LOOP

---------------

DC R1

DCR 2

3000

Iringlim

----------------------

19 ms

DC 1

DC2

DC1 RDC 2

---------------------------------

•

DC R

DCR1

DC R2

DC R1RDCR2

----------------------------------------

• 150 µs

LTH

12.67

•

LTH

12.67

-------------

LTH

11.37

-------------

LTH

BAT1

–

915

-----------------------------

•

400

–

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