HC5503CBZ Intersil, HC5503CBZ Datasheet - Page 6

• Manufacturer Part Number: HC5503CBZ
• Manufacturer: Intersil

Specifications of HC5503CBZ

• Number Of Channels: 1
• On-hook Transmission: Yes
• Polarity Reversal: No
• On-chip Ring Relay Driver: Yes
• Longitudinal Balanced: 58
• Operating Supply Voltage (typ): 5V
• Operating Temp Range: 0C to 70C
• Loop Current Limit: 30mA
• Operating Temperature Classification: Commercial
• Pin Count: 24
• Mounting: Surface Mount
• Operating Supply Voltage (max): 5.25V
• Operating Supply Voltage (min): 4.75V
• Lead Free Status / RoHS Status: Compliant

Design Information
Line Feed Amplifiers
The line feed amplifiers are high power operational
amplifiers and are connected to the subscriber loop through
150Ω of feed resistance as shown in Figure 1. The feed
resistors and synthesized impedance via feedback provide a
600Ω balanced load for the 2-wire to 4-wire transmission.
The tip feed amplifier is configured as a unity gain
noninverting buffer. A -4V bias (derived from the negative
battery (V
the amplifier. Hence, the tip feed DC level is at -4V. The
principal reason for this offset is to accommodate sourcing
and sinking of longitudinal noise currents up to 15mA
without saturating the amplifier output and to provide
sufficient overhead for receive signals. The tip feed amplifier
also feeds the ring feed amplifier, which is configured as a
unity gain inverting amplifier as seen from the tip feed
amplifier. The noninverting input to the ring feed amp is
biased at a V
has a noninverting gain of 2. Thus, the DC output at ring
feed is:
V
For a -24V battery, V
feed across the loop provided by the SLIC is 16V. When the
subscriber goes off-hook this DC feed causes current
(metallic current) to flow around the loop.
NOTE: Grounded for AC analysis.
RF
(DC) = (4 + V
BAT
R
Z
IN
B1
BAT
) in the bias network) is applied to the input of
= R
/2. Looking into this terminal the amplifier
RING
BAT
B2
TIP
= R
RF
) Volts
S
-
150Ω
= -20V. Hence, the nominal battery
150Ω
+
= 150Ω
R
∆I
R
∆I
B2
L
B1
L
+
-
6
RING FEED
TIP FEED
FIGURE 1. IMPEDANCE MATCHING CIRCUITRY
R
+
-
Va
+
-
RMS
-
+
R
V
BAT
HC5503
2
90kΩ
+
+
-
-
+ 4V
-
+4RS∆I
(NOTE)
The received audio signal RX is fed into the tip feed amplifier
and appears at the tip feed terminal. It is also fed through the
ring feed amplifier and is inverted. Thus, a differential signal
of 2V
signal causes AC audio currents to flow around the loop
which are then AC coupled to the earpiece of the telephone
set.
2-Wire Impedance Matching
The HC5503 is optimized for operation with a -24V battery.
Impedance matching to a 600Ω load, is achieved through
the combination of the feed resistors (R
negative feedback through resistor R
R
and provide negative feedback to synthesize the remaining
300Ω required to match a 600Ω line.
The impedance looking into the tip terminal is 150Ω (R
plus the synthesized impedance of the tip amplifier. The
synthesized tip impedance is equal to the tip feed voltage Va
divided by ∆IL. (Note, the tip feed amplifier is a voltage
follower. Thus, the tip feed voltage is equal to the receive
input voltage V
impedance of the ring terminal is calculated the same way
and is the ring feed voltage divided by ∆IL. (Note, the ring
feed voltage is equal in magnitude to the tip feed voltage, but
opposite in phase as a result of the ring feed amplifier gain.)
HC5503
DC
(NOTE)
B1
L
RX
+ 2
-
and R
RX
appears between tip feed and ring feed. The R
4RS∆I
B2
+
TX
C
L
are sense resistors that detect loop current
3
RX
, both are labeled Va.) The synthesized
R
3
C
4
TO TRANSHYBRID OP-AMP
R
R
2
1
2
V
IN
(reference Figure 1).
B1
, R
INPUT
FROM
CODEC
B2
) and
B1
X
)