Datasheet LA4160 (Sanyo) - 7

LA4160
3. Power Amplifier The power amplifier circuit consists of the differential stage (TR22, 23), predriver stage (TR41), driver stage (TR42,
44), and output stage (TR47,48). Bias resistor R36 of TR20 at the first stage is attached externally and the input
impedance depends on this R36. Input pin (4) whose potential is nearly equal to the ground potential can be connected
direct to the variable resistor without using an input coupling capacitor. The closed loop voltage gain is obtained by the
following equation.
R19
VG (pwr) = 20 log
( R18 + Rf )
Since R19 = 20kΩ, R18 = 50Ω are set, approximately 52dB max. is available if Rf = 0 is taken. Proper Cares in Using IC
1. Printed Circuit Board
For the printed circuit board layout, refer to the printed circuit pattern example in principle. It is necessary that the
grounding points of the power amplifier input (variable resistor), pin (3) feedback resistor (Rf), and bias resistor
(R35) should be adjacent to one another. Especially, it should be noted that if a common impedance exists in the
variable resistor grounding, the distortion, residual ripple, and cross interference (leak of signal between
preamplifier and power amplifier) may worsen. 8 14 LA4160
7 1
R1 To preamplifier
Make adjacent to one another. VR
R35 2. Oscillation
[Measures against oscillation]
a) Preamplifier
Since oscillation may osccur when used at a low voltage
Approximately
8
gain, a capacitor of approximately 10pF must be connected
9
across pins (8) and (6) for phase compensation. If the
6
Preamp.
capacitor connected across pins (8) and (6) has a large
RL
0.01μF
capacitance at a low load impedance, further oscillation
1000pF
(Polyester
film
may occur, and in this case the load pin must be grounded
capacitor)
through a capacitor of approximately 0.01μF (Polyester
film capacitor). The input pin must be grounded through a capacitor of approximately 1000pF for the purpose of
prevention of radio disturbance and oscillation.
No.870-7/11