HC5549_14 Datasheet, PDF (6/13 Pages) Intersil Corporation – Low Power SLIC with Battery Switch

HC5549
4-WIRE TO 2-WIRE GAIN
The 4-wire to 2-wire gain is defined as the receive gain. It is
a function of the terminating impedance, synthesized
impedance and protection resistors. Equation 6 calculates
the receive gain, G₄₂.
G₄₂
=
–2



Z^----_O^-------+^-----2^--Z--R^--L---_P^-----+^------Z^----_L^-_{}
(EQ. 6)
When the device source impedance and protection resistors
equals the terminating impedance, the receive gain equals
unity.
2-WIRE TO 4-WIRE GAIN
The 2-wire to 4-wire gain (G₂₄) is the gain from tip and ring to
the VTX output. The transmit gain is calculated in Equation 7.
G₂₄
=
–

Z^----_O^-------+^-----2^--Z--R^--O---_P^-----+^------Z^----_L^-_{}
(EQ. 7)
When the protection resistors are set to zero, the transmit
gain is -6dB.
TRANSHYBRID GAIN
The transhybrid gain is defined as the 4-wire to 4-wire gain
(G₄₄).
G₄₄
=
–

Z^----_O^------+-----2^-Z---R^-O---_P^-----+-----Z^----_L^-_{}
(EQ. 8)
When the protection resistors are set to zero, the transhybrid
gain is -6dB.
COMPLEX IMPEDANCE SYNTHESIS
Substituting the impedance programming resistor, R_S, with a
complex programming network provides complex
impedance synthesis.
2-WIRE
NETWORK
C₂
R₁
R₂
PROGRAMMING
NETWORK
C_P
R_S
R_P
FIGURE 1. COMPLEX PROGRAMMING NETWORK
The reference designators in the programming network
match the evaluation board. The component R_S has a
different design equation than the R_S used for resistive
impedance synthesis. The design equations for each
component are provided below.
R_S = 400 × (R₁ – 2(R_P))
(EQ. 9)
R_P = 400 × R₂
C_P = C₂ ⁄ 400
(EQ. 10)
(EQ. 11)
Low Power Standby
Overview
The low power standby mode (LPS, 000) should be used
during idle line conditions. The device is designed to operate
from the high battery during this mode. Most of the internal
circuitry is powered down, resulting in low power dissipation.
If the 2-wire (tip/ring) DC voltage requirements are not
critical during idle line conditions, the device may be
operated from the low battery. Operation from the low battery
will decrease the standby power dissipation.
TABLE 1. DEVICE INTERFACES DURING LPS
INTERFACE ON
OFF
NOTES
Receive
Ringing
Transmit
x AC transmission, impedance
matching and ringing are
x
disabled during this mode.
x
2-Wire
x
Amplifiers disabled.
Loop Detect
x
Switch hook or ground key.
2-WIRE INTERFACE
During LPS, the 2-wire interface is maintained with internal
switches and voltage references. The Tip and Ring
amplifiers are turned off to conserve power. The device will
provide MTU compliance, loop current and loop supervision.
Figure 2 represents the internal circuitry providing the 2-wire
interface during low power standby.
GND
600Ω
TIP AMP
TIP
RING
RING AMP
600Ω
MTU REF
FIGURE 2. LPS 2-WIRE INTERFACE CIRCUIT DIAGRAM
MTU Compliance
Maintenance Termination Unit or MTU compliance places
DC voltage requirements on the 2-wire terminals during idle
line conditions. The minimum idle voltage is 42.75V. The
high side of the MTU range is 56V. The voltage is expressed
as the difference between Tip and Ring.
The Tip voltage is held near ground through a 600Ω resistor
and switch. The Ring voltage is limited to a maximum of
-49V (by MTU REF) when operating from either the high or
low battery. A switch and 600Ω resistor connect the MTU
reference to the Ring terminal. When the high battery
6
FN4539.3