TS486-TS487
27/31
APPLICATION NOTE:
TS486/487 GENERAL DESCRIPTION
TS486/487 is a family of dual audio amplifiers able
to drive16
or 32
headsets. Working in the 2V to
5.5V supply voltage range, they deliver 100mW at
5V and 12mW at 2V in a 16
load. An internal
output current limitation, offers protection against
short-circuits at the output over a limited time
period.
Fixed gain versions of the TS486 and TS487
including the feedback resistor and the input
resistors are also proposedto reduce the number
of external parts.
The TS486 and TS487 exhibit a low quiescent
current of typically 1.8mA, allowing usage in
portable applications.
The
SHUTDOWN input.
TS487), the deviceis in sleep modewhen PIN 5 is
connected at GND (resp. V
CC
).
standby
mode
is
selected
TS486 (respectively
using
the
For
GAIN SETTING
The gain of each inverter amplifier of the TS486
and TS487 is set by the resistors R
IN
and R
FEED
.
Gain
LINEAR
= -(R
FEED
/R
IN
)
Gain
dB
= 20 Log(R
FEED
/R
IN
)
Fixed
including R
IN
and R
FEED
are proposed to reduce
external parts.
gain versions
TS486-n and
TS487-n
LOW FREQUENCY ROLL-OFF WITH INPUT
CAPACITORS
The low roll-off frequency of the headphone
amplifiers depends on the input capacitors C
IN1
and C
IN2
and the input resistors R
IN1
and R
IN2
.
The C
IN
capacitor in series with the input resistor
R
IN
of the amplifier is equivalent to a first order
high pass filter.
Assuming that F
min
is the lowest frequency to be
amplified (with a 3dB attenuation), the minimum
value of C
IN
is:
C
IN
> 1 / (2*
π
*F
min
*R
IN
)
The
frequency roll-off versus the input capacitor C
IN
following curve
gives
directly
the
low
20k
20k
20k
20k
Vcc
+
220
μ
F
+
220
μ
F
Right In
Left In
+
ZL=32Ohms
+
ZL=32Ohms
+
1
μ
F
+
330nF
+
330nF
+
Cs
1
μ
F
Cin1
Cin2
Rin1
Cout2
Cout1
Rin2
Rfeed1
Rfeed2
Cb
+
-
+
-
8
VCC
4
1
7
2
3
5
6
BIAS
TS486=Stdby
TS487=Stdby
GND
Stdby
Stdby level
threshold=0.9V
Stdby ctrl
1k
1k