Le7920
Data Sheet
Table 1. SLIC Decoding
State
C2
C1
0
Two-Wire Status
DET Output
Ring trip
0
1
2
3
0
0
1
1
Disconnect
Ringing
Active
1
Ring trip
0
Loop detector
Loop detector
1
Standby
Table 2. User-Programmable Components
ZT is connected between the VTX and RSN pins. The fuse
ZT = 250(Z2WIN – 2RF)
resistors are RF, and Z2WIN is the desired 2-wire AC input
impedance. When computing ZT, the internal current amplifier
pole and any external stray capacitance between VTX and RSN
must be taken into account.
ZL
G42L
500ZT
ZT + 250(ZL + 2RF)
ZRX is connected from VRX to RSN. ZT is defined above, and
G42L is the desired receive gain.
------------
---------------------------------------------------
ZRX
=
•
1250
R
DC1 + RDC2 = ---------------
ILOOP
RDC1, RDC2, and CDC form the network connected to the RDC
pin. RDC1 and RDC2 are approximately equal. ILOOP is the
desired loop current in the constant-current region.
R
R
DC1 + RDC2
DC1 • RDC2
----------------------------------
CDC = 1.5 ms •
RD and CD form the network connected from RD to AGND/
DGND and IT is the threshold current between on hook and
off hook.
510
415
0.5 ms
RD
--------
IT
--------
IT
RDON
=
, RDOFF
=
, CD = ----------------
1
CCAS = ------------------------------
CCAS is the regulator filter capacitor and fc is the desired filter
cut-off frequency.
5
3.4 • 10 πfc
VBAT – 3 V
ISTANDBY = ---------------------------------
Standby loop current (resistive region).
400 Ω + RL
Thermal Management Equations (Normal Active and Tip Open States)
VBAT – 6 V
RTMG is connected from TMG to VBAT and saves power within
the SLIC in Active and Disconnect state constant-currents only.
RTMG ≥ --------------------------------- – 70 Ω
ILOOP
2
( VBAT – 6 V – (IL • RL))
------------------------------------------------------------------------
PRTMG
=
• RTMG
Power dissipated in the TMG resistor, RTMG, during Active and
Disconnect states.
2
(RTMG + 70 Ω)
Power dissipated in the SLIC while in Active and Disconnect
states.
PSLIC = VBAT • IL – PRTMG – RL(IL)2 + 0.12 W
11
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
