TECHNICAL DATA
1
Low Voltage Audio Power AMP
The IL386 is a power amplifier designed for use in low voltage
consumer applications. The gain is internally set to 20 to keep external
part count low, but the addition of an external resistor and capacitor
between pins 1 and 8 will increase the gain to any value up to 200.
The inputs are ground referenced while the output is automatically
biased to one half the supply voltage. The quiescent power drain is
only 24 milliwatts when operating from a 6 volt supply, making the
IL386 ideal for battery operation.
Battery Operation
Minimum External Parts
Wide Supply Voltage Range: 4 V - 12 V
Low Quiescent Current Drain: 4 mA
Voltage Gains from 20 to 200
Ground Referenced Input
Self-Centering Output Quiescent Voltage
Low Distortion
Eight Pin Dual-In-Line Package
IL386
ORDERING INFORMATION
IL386N Plastic
IL386D SOIC
T
A
= 0
to 70
C for
package
PIN ASSIGNMENT
LOGIC DIAGRAM
Pin 4 = GND
Pin 6 = Supply Voltage V
+
IL386
2
MAXIMUM RATINGS
*
Symbol
Parameter
Value
Unit
V
CC
Supply Voltage
15
V
V
IN
Input Voltage
0.4
V
P
D
Power Dissipation
1.25
W
Tstg
Storage Temperature
-65 to +150
C
T
J
Junction Temperature
+150
C
T
L
Lead Temperature
+300
C
*
Maximum Ratings are those values beyond which damage to the device may occur.
Functional operation should be restricted to the Recommended Operating Conditions.
RECOMMENDED OPERATING CONDITIONS
Symbol
Parameter
Min
Max
Unit
V
CC
Supply Voltage
4.0
12
V
T
A
Operating Temperature, All Package Types
0
+70
C
This device contains protection circuitry to guard against damage due to high static voltages or electric
fields. However, precautions must be taken to avoid applications of any voltage higher than maximum rated
voltages to this high-impedance circuit. For proper operation, V
IN
and V
OUT
should be constrained to the range
GND
(V
IN
or V
OUT
)
V
CC
.
Unused inputs must always be tied to an appropriate logic voltage level (e.g., either GND or V
CC
).
Unused outputs must be left open.
ELECTRICAL CHARACTERISTICS
(T
A
= 25
C)
Symbol
Parameter
Test Conditions
Guaranteed Limits
Unit
Min
Typ
Max
V
+
Operating Supply
Voltage
4
12
V
I
+
Quiescent Current
V
+
= 6 V, V
IN
= 0
8
mA
P
O
Output Power
V
+
= 6V, R
L
=8
, THD=10%
V
+
= 9V, R
L
=8
, THD=10%
325
1000
mW
A
V
Voltage Gain
V
+
= 6V, f=1kHz
10
F from Pin 1 and 8
26
46
dB
BW
Bandwidth
V
+
= 6V, Pins 1 and 8 Open
250
KHz
THD
Total Harmonic
Distortion
V
+
= 6V, R
L
=8
, P
OUT
=125mW,
f=1kHz,
Pins 1 and 8 Open
1.0
%
PSRR
Power Supply Rejection
Ratio
V
+
= 6V, f=1kHz, C
BYPASS
=10
F,
Pins 1 and 8 Open
45
dB
R
IN
Input Resistance
30
80
K
I
B
Input Bias Current
V
+
= 6V, Pins 2 and 3 Open
250
nA
IL34119
3
APPLICATION INFORMATION
GAIN CONTROL
To make the IL386 a more versatile amplifier, two
pins (1 and 8) are provided for gain control. With
pins 1 and 8 open the 1.35 K
resistor sets the gain
at 20 (26 dB). If a capacitor is put from pin 1 to 8,
bypassing the 1.35 K
resistor, the gain will go up to
200 (46 dB). If a resistor is placed in series with the
capacitor, the gain can be set to any value from 20 to
200. Gain control can also be done by capacitively
coupling a resistor (or FET) from pin 1 to ground.
Additional external components can be placed in
parallel with the internal feedback resistors to tailor
the gain and frequency response for individual
applications. For example, we can compensate poor
speaker bass response by frequency shaping the
feeback path. This is done with a series RC from pin
1 to 5 (paralleling the internal 15 K
resistor). For
6 dB effective bass boots: R
15 K
, the lowest
value for good stable operation is R=10 K
if pin 8
is open. If pins 1 and 8 are bypassed then R as low as
2 K
can be used. This restriction is because the
amplifier is only compensated for closed-loop gains
greater the 9.
INPUT BIASING
The schematic shows that both inputs are biased to
ground with a 50 K
resistor. The base current of
the input transistors is about 250 nA, so the inputs
are at at out 12.5 mV when left open. If the dc source
resistance oriving the IL386 is higher than 250 K
it
will contribute very little additional offset (about
2.5 mV at the input, 50 mV at the output). If the dc
source resistance is less than 10 K
, then shorting
the unused input to ground will keep the offset low
(about 2.5 mV at the input, 50 mV at the output). For
dc source resistances between these values we can
eliminate excess offset by putting a resistor from the
unesed input to ground, equal in value to the dc
source resistance. Of course all affset problems are
eliminated if the input is capacitively coupled.
When using the IL386 with higher gains (by pessing
the 1.35 K
resistor between pins 1 and 8) it is
necessary to bypass the unused input, preventing
degradation of gain and possible instabilities. This is
done with a 0.1
F capacitor or a short to ground
depending on the dc source resistance on the driven
input.
SCHEMATIC DIAGRAM
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