HC5520
HC5520
A = 400
R
4W
+
TIP
V
TX
A2
-
∆I
-
+
KZO
∆I
TS
R
R
TPS
∆I
∆I
RS
∆I
TS
L
Z
∆I
RX
L
∆V
TR
R
X
+
∆I
RS
+
V
RX
-
RGS
E
G
R
N
-
A = 400
∆I
A1
KZO
2x∆I
∆I
RX
∆I
RS
TS
+
RING
Z
KZO
-
∆I
KZO
FIGURE 2. SIMPLIFIED AC TRANSMISSION CIRCUIT
C
VRX
R
TPS
100kΩ
0.47µF
V
RX
50kΩ
62pF
TIPSEN
TIP
R
X
TIP
R
X
50kΩ
100kΩ
100kΩ
R
50Ω
PT
0.47µF
-
+
HC5520
600Ω
R
50Ω
R
PR
VOICE INPUT
AMPLIFIER
4W
100kΩ
100kΩ
RING
T
X4W
RING
RINGSEN
T
X
C
V
R
VTX
TX
RGS
0.47µF
100kΩ
FIGURE 3. TRANSHYBRID BALANCE CIRCUIT WITH HIGH AND LOW FREQUENCY COMPENSATION
K
Pin - The 2-wire impedance that is synthesized by the
C
Pin - This pin provides a connection to the DC refer-
ZO
DC
HC5520 is a direct function of the network connected to this ence nodes that control the DC loop feed current. These
pin (see equations). Parasitic capacitance and inductance internal blocks are referenced to V and it is important that
EE
from the PC board layout and the external components is the capacitor be referenced to V or else the PSRR perfor-
EE
magnified by the same K factor that is utilized to synthesize mance will be degraded.
the 2-wire impedance. Excessive parasitics can cause inser-
tion loss and return loss degradation, especially at higher
voice band frequencies. Good PC board layout techniques
and proper component selection can minimize these effects
to a negligible level.
C Pin - Capacitor C connects to this pin to create a low-
P
P
pass filter for the half-battery internal reference point. It is
important that this capacitor be referenced to BGND/AGND
to minimize the effect of noise injected into the subscriber
loop from the battery supply.
R Pin - This pin connects an external resistor to the input
N
R
, R
, R
, R
Pins - These pins are connected
PSB
PSG
PST
PSR
of an internal buffer. The value of this resistor is user speci-
fied based upon the impedance desired at the 2-wire inter-
face (see equations). The value chosen must not have a
value greater than 7kΩ or the input voltage range of the
buffer may be exceeded during transients.
to critical nodes inside the HC5519R3931 feedback control
loops. Parasitic capacitance should be minimized in order to
prevent oscillations.
RD, TB, TA Pins - The pins connect to the driver coils of the
Ring and Test relays and activate the relays by pulling down
the coil voltage to ground. The driver outputs are internally
R
Pin - An external resistor connected to V is required
CC
DC
at this pin to provide an accurate reference for the DC cur-
rents which feed the subscriber loop. PC board traces
should be made to have low resistance and should connect
clamped to V
by diodes to prevent the inductive voltage
transient during relay turn-off from damaging the driver.
CC
Relays attached to any voltage other than V
tion properly.
will not func-
CC
directly to V
.
CC
8
HARRIS [ HARRIS CORPORATION ]
