la4814v Sanyo Semiconductor Corporation, la4814v Datasheet - Page 5

• Manufacturer Part Number: la4814v
• Description: 2-channel Power Amplifier
• Manufacturer: Sanyo Semiconductor Corporation

Cautions for Use
1.Input coupling capacitors (C1, C2)
2.Pin 7 capacitor (C5)
3.Bypass capacitor (C7)
4.Standby function
C1 and C2 are input coupling capacitors that are used to cut DC voltage. However, the input coupling capacitor C1 (C2)
and input resistor R1 (R2) make up the high-pass filter, attenuating the bass frequency. Therefore, the capacitance value
must be selected with due consideration of the cut-off frequency.
The cut-off frequency is expressed by the following formula :
Note with care that this capacitance value affects the pop noise at startup. To increase this capacitance value, it is
necessary to increase the capacitance value of pin 7 capacitor (C5) to soften the startup characteristics.
This capacitor C5 is designed for the ripple filter. Its purpose is to make up a low-pass filter with a 100kΩ internal
resistor for reducing the ripple component of the power supply and improve the ripple rejection ratio.
Inside the IC, the startup characteristics of the pin 7 voltage are used to drive the automatic pop noise reduction circuit,
and care must be taken with the pop noise when the C5 capacitance value is to be set lower.
However, when the IC is used in BTL mode, the automatic pop noise reduction function mentioned above has no effect.
Instead, a pop noise reduction method that utilizes the second amplifier control function is used so that the capacitance
value must be determined while factoring in the ripple rejection ratio or startup time.
The purpose of the bypass capacitor C7 is to reject the high-frequency components that cannot be rejected by the power
supply capacitor (chemical capacitor C6). Place the capacitor as near to the IC as possible, and use a ceramic capacitor
with excellent high-frequency characteristics.
The standby function serves to place the IC in standby mode to minimize the current drain.
a) When using the standby function (when using microcomputer control)
b) When not using the standby function (microcomputer control is not possible)
By applying the following voltages to the standby pin (pin 8), the mode changeover can be performed between
standby and operation.
However, set the resistance of resistor R5 inserted in series in such a way that the condition in the following formula
is met.
The pin 8 inrush current is expressed by the following formula:
By applying a voltage from the power supply (pin 14) to the standby pin (pin 8), the IC can be turned on without the
control of the microcomputer when the power is turned on.
In order to reduce the pop noise when the IC is turned off, it is recommended that resistor R5 be inserted as shown in
Fig.2. The resistance value indicated below is recommended for the inserted resistor R5.
Operation mode … V8 ≥ 1.6V
Standby mode … V8 ≤ 0.3V
R5 ≤ 24.6 × (Vstby - 1.6) kΩ
I8 = (40 × Vstby - 26.3)/(1+0.04 × R5) μA
V CC = 5.0V : R5 = 82kΩ
V CC = 3.6V : R5 = 47kΩ
V CC = 3.0V : R5 = 33kΩ
fc = 1/2 π × R1 × C1 (= 1/2 π × R2 × C2)
Recommended capacitance value : Min. 22μF (in 2-channel mode)
10μF (in mono BTL mode)
LA4814V
V CC
Fig. 2
R5
Vstby
14
8
Fig. 1
V CC
STBY
R5
V8
8
STBY
No.A0972-5/17