la4809m Sanyo Semiconductor Corporation, la4809m Datasheet - Page 6

• Manufacturer Part Number: la4809m
• Description: Monolithic Linear Ic Stereo Headphone Amplifier
• Manufacturer: Sanyo Semiconductor Corporation

Cautions for use
1. Input coupling capacitors (Cin1, Cin2)
2. Output coupling capacitors (Cout1, Cout2)
3. Power supply line capacitor (CV CC )
4. Pin 2 capacitor (Crf)
5. Voltage gain
6. Load capacitance
Cin1 (Cin2) is an input coupling capacitor, which is intended for DC cut. This capacitor forms a high pass filter
together with the internal resistance of 45kΩ attenuating the bass frequency signal. Set the capacitance value with due
consideration of the cut-off frequency.
Note that the cut-off frequency is expressed as follows :
This capacitor also affects the pop noise at a time of falling. Note that setting the higher capacitance value causes delay
of the capacitor discharge rate, causing louder pop noise.
Cout1 (Cout2) is an output coupling capacitor, which is intended for DC cut. This capacitor forms a high pass filter
together with the load impedance of R L , attenuating the bass frequency signal. Set the capacitance value with due
consideration of the cut-off frequency. Normally, the chemical capacitor is used. When setting the capacitance value,
take into account the characteristics of the chemical capacitor, namely, the capacitance value of chemical capacitor
tends to decrease at low temperature.
Note that the cut-off frequency is expressed as follows :
This capacitor also affects the pop noise at a time of rising. Note that setting the higher capacitance value causes louder
pop noise.
CV CC is intended to stabilize the power supply line. Arrange this capacitor as near to IC as possible and always use the
ceramic capacitor with superior high frequency characteristics.
Increase the capacitance value when the power supply line is relatively unstable.
Crf is a capacitor to determine the transient response characteristics of the Pin 2 voltage (reference voltage) : Vrf. At a
time of rising, this is charged by the internal constant-current source (about 39μA). At a time of falling, this is
discharged by the internal resistance (about 157kΩ). Due attention must be paid because pop noise and the amplifier
rise / fall time change depending on the transient response characteristics of Pin 2 voltage. Decreasing the capacitance
value to shorten the response time, pop noise becomes louder. Therefore, the use of the value shown below as the
capacitance value is recommended. As this capacitor reduces the power supply ripple component, decrease in the
capacitance value results in lowering of the ripple removal ratio.
The voltage gain of amplifier is determined by the internal resistance and is fixed at about 11.7dB. When the output
level is to be changed, attempt attenuation with the resistor in the forward stage of input as shown in Fig.1. To enhance
the degree of attenuation, use two resistors as shown in Fig.2 so as to reduce internal-resistor variation factors.
Though attenuation in the backward stage of output as shown in Fig.3 is possible, this may cause decrease in the
maximum output power.
When connecting a capacitor between the output pin and GND for an anti-electric wave radiation measure, this
capacitor may cause decrease in the phase margin of power amplifier, resulting in the oscillation phenomenon. When
connecting this capacitor, pay attention to its capacitance value.
other IC
OUT
(Low attenuation degree)
1ch ⇒ fc1 = 1/ (2π × Cin1 × 45000)
2ch ⇒ fc2 = 1/ (2π × Cin2 × 45000)
1ch ⇒ fc3 = 1/ (2π × Cout1 × R L )
2ch ⇒ fc4 = 1/ (2π × Cout2 × R L )
Crf recommended values : 1μF to 3.3μF
Recommended capacitance value : 560pF or less, or 0.01μF to 0.1μF
Fig.1
LA4809M
IN
other IC
OUT
(High attenuation degree)
LA4809M
Fig.2
LA4809M
IN
LA4809M
OUT
Fig.3
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No.A1569-6/15