LA4422 데이터 시트보기 (PDF) - SANYO -> Panasonic
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LA4422 Datasheet PDF : 10 Pages
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LA4422
Functions of External Parts
The recommended number of external parts of the LA4422 is 4 pcs. as follows.
· Feedback capacitor from pin (5) CNF.
· Pin (7) to (10) bootstrap capacitor CBS.
· Output capacitor from pin (10) COUT.
· High frequency parasitic oscillation compensating capacitor CX.
The fixed values of these parts are CNF=100µF, CBS=100µF, COUT=1000µF, CX=0.15µF. We now consider what will occur
when these values are changed.
(a) Feedback capacitor CNF
If CNF is made smaller, the combined series impedance with RNF at a low frequency is increased, the amplification
degree Avf is decreased, and the low cutoff frequency is made higher as seen from the following equation.
Rf
Avf=
(RNF+
1
jωCNF
)
VG=20log Avf (dB)
The ripple rejection is also lowered. It is possible, however, to make the starting time earlier at the time of the power
supply switch ON. If CNF is made larger, these are reversed.
(b) Bootstrap capacitor CBS
The low cutoff frequency may be somewhat influenced, but the drive at a low frequency is more influenced. If CBS is
made smaller, power at a low frequency may be reduced. Therefore, CBS should be more than 47µF.
(c) Output capacitor COUT
The low cutoff frequency may be somewhat influenced, but the most influence is that power is reduced as the imped-
ance at a low frequency is increased. Therefore, COUT should be determined by the power band width. 470µF min. is
required.
(d) High frequency parasitic oscillation compensating capacitor CX.
CX should be a polyester film capacitor of good frequency characteristic. If a ceramic capacitor is used, oscillation may
occur.
Features of IC System and Functions of Remaining Pins
· Since the input circuit uses pnp and the input potential is designed to be 0 bias, no input coupling capacitor is needed and
the direct coupling is available.
· The thermal shutdouwn protection circuit is built in to prevent breakdown or degradation attributable to generation of heat
at the time of load short or overload.
· The overvoltage protection circuit is built in to protect the IC from breaking down when a surge is applied to the power
supply line.
· The prevention circuit is provided to prevent pop noise which occures when the power supply is turned ON.
· The voltage gain of open loop is lowered and the nagative feedback is made smaller to obtain a soft clip. Radiation to the
high frequency circuit and stability are considered.
· The feedback resistor Rf is set up at such a large value as 40kΩ and the cutoff frequency point fL is considered so that the
frequency characteristic is fully externded to a low frequency even if the capacity of capacitor CNF is small.
· The high frequency parasitic oscillation compensating capacitor is built in as a means to reduce the number of external
parts. Therefore, the high cutoff frequency point fH is fixed.
· The feedback resistor RNF is built in and the voltage gain is fixed to be 53dB in order to reduce the number of external
parts and to minimize the variations of voltage gain.
Pins (5) and (6) are provided to control the voltage gain externally. The voltage gain is lowered by inserting a resistor in
series with pin (5). The voltage gain is increased by inserting a resistor between pin (5) and (6). If CR are connected to
pin (6), the voltage gain is freely controlled through pin (6) alone.
· Pin (4) is provided as a decoupling pin.
Even if the power suppy is turned ON/OFF in succession, pop noise is minimized by connecting a capacitor to this pin,
provided that a condition CD≥CNF is recommended. CNF is related to the starting time. The ripple rejection is improved
by connecting the decoupling capacitor CD.
No.556–3/10
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