LA4268
No.7093-3/5
Description of External Parts
C1: Ripple filter capacitor
Decreasing the capacitance value reduces ripple rejection. This capacitor also affects the starting time; decreasing
the capacitance value makes the starting time earlier.
C2: Input capacitor
Because the DC potential of the input pin is not zero, this capacitor can not be omitted. Decreasing the capacitance
value to an extremely low level lowers the low frequency response.
C3: Feedback capacitor
Decreasing the capacitance value lowers the low frequency response. Increasing the capacitance value makes the
starting time later.
C4: Output capacitor
Decreasing the capacitance value causes insufficient power at low frequencies.
C5: Oscillation blocking capacitor
Decreasing the capacitance value causes oscillation to occur easily. Use a polyester film capacitor that has good
high frequency response and temperature characteristics.
The use of an electrolytic capacitor or a ceramic capacitor may cause oscillation to occur at low temperatures.
C6: Power capacitor
Decreasing the capacitance value causes ripple to occur easily. Locating at a distance from the IC or removing this
capacitor may cause oscillation to occur.
R1: Mute resistor
Refer to supplementary discussion “External Muting.’’
R2: Resistor connected in series with oscillation blocking capacitor
Prevents phase shift in conjunction with the oscillation blocking capacitor so that oscillation does not easily occur.
There is an optimal value for the resistor; increasing or decreasing the resistance causes oscillation to occur easily.
External Muting
Pull down the electric potential of the ripple filter pin (pin 3).
Muting becomes possible by inserting the discharge resistor R1
between pin 3 and GND. If the resistance value of R1 is too low, a
popping noise is generated; if the resistance value is too high, the
muting effect is reduced. (A value of 750
is recommended for R1.)
Voltage Gain
The voltage gain is fixed at 40dB by the ratio of the 30k
and 300
internal resistors. Therefore, it is not possible to use this IC with a
voltage gain greater than 40dB. Although it is possible to use this IC
with a voltage gain of less than 40dB by adding a feedback resistor
(RNF) and external resistors (R) as shown in the diagram, doing so
causes oscillation to occur easily. Therefore, do not use this IC with a
voltage gain of 30dB or less.
Notes on Using the IC
Maximum ratings
When this IC is used near its maximum ratings, it is possible that a slight fluctuation in the operating conditions
could cause the maximum ratings to be exceeded, damaging the IC. Therefore, allow for an adequate safety margin
in regards to supply voltage, etc., so that the IC is never used under conditions that exceed its maximum ratings.
Short circuit between pins
Applying power to the IC while a short circuit exists between two pins can cause damage or deterioration in the IC.
Therefore, after mounting the IC on a board, make sure that there are no solder bridges, etc., causing a short circuit
between any of the pins before applying power to the IC.
Using the IC in a radio
When using this IC in a radio, make sure that there is enough distance between the IC and the bar antenna.
Printed circuit pattern
When designing the printed circuit pattern, keep power, output, and ground lines thick and short, and determine the
placement of the pattern and the components in such a way as to prevent the generation of an I/O feedback loop.
In addition, power supply capacitor C6 and oscillation blocking capacitor C5 should be placed as close as possible to
the IC pins in order to prevent oscillation.