
Usage Notes
Speech Network Circuit Block
External driver transistor
No. 6471-17/29
LA8519M
+
49
48
VL
TOI
S-VCC
50 TOO
LA8519M
51 BN1
52 BN2
47
7.5k
51
C1
R1
Tr
82
82
620
R3
220
μ
F
C2
3.3k
8.2
R2
8.2k
5.6k
1.3k
1.8k
8200pF
6800pF
A13123
4
5
2
3
6
7
8
9
10
11
12
10
20
30
40
50
Line current — mA
90
100
110 120 130
Figure 1
Line
Since the IC includes a built-in power amplifier, due to the allowable power dissipation limits, include a heat
dissipation transistor as shown in figure 1, and dissipate the circuit current outside the IC. Set the allowable power
dissipation for R1 and R2 according to the maximum expected circuit current. (The values shown are for reference
purposes only.)
Note: If oscillation occurs due to the load state between VL and ground, insert the capacitor C1 (about 0.1 μF)
shown in the figure.
Changing the DC resistance
The DC resistance can be modified by using a variable resistor for R2 in figure 1. (See the figure below.)
Note: Note that changing R2 will also change the transmitter gain and the balancing network conditions.
Determining the AC impedance
The AC impedance is basically determined by R3 (620
) and C2 (220 μF) shown in figure 1 above page. Since in
actual operation there will be other AC loads in addition to the speech network, adjust the total AC impedance for
the whole system in combination with the speech network impedance.
Note: Note that if R3 is changed, the DC resistance will change as well.
Line Voltage vs. Line Current
L
Power supplied: V
CC
= 5 V
Power supplied: R2 = 10
Power off: R2 = 10
Power supplied: R2 = 8.2
Power off: R2 = 8.2
Power supplied: R2 = 6.8
Power off: R2 = 6.8