Datasheet

TS419-TS421
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APPLICATION INFORMATION
■ BTL Configuration Principle
The TS419 & TS420 are monolithic power
amplifiers with a BTL output type. BTL (Bridge
Tied Load) means that each end of the load is
connected to two single-ended output amplifiers.
Thus, we have:
Single ended output 1 = Vout1 = Vout (V)
Single ended output 2 = Vout2 = -Vout (V)
And Vout1 - Vout2 = 2Vout (V)
The output power is :
For the same power supply voltage, the output
power in BTL configuration is four times higher
than the output power in single ended
configuration.
■ Gain In Typical Application Schematic
(cf. page 3 of TS419-TS421 datasheet)
In the flat region (no C
IN
effect), the output voltage
of the first stage is:
For the second stage : Vout2 = -Vout1 (V)
The differential output voltage is
The differential gain named gain (Gv) for more
convenient usage is :
Remark : Vout2 is in phase with Vin and Vout1 is
phased 180° with Vin. This means that the positive
terminal of the loudspeaker should be connected
to Vout2 and the negative to Vout1.
■ Low and high frequency response
In the low frequency region, C
IN
starts to have an
effect. C
IN
forms with R
IN
a high-pass filter with a
-3dB cut off frequency .
In the high frequency region, you can limit the
bandwidth by adding a capacitor (Cfeed) in
parallel with Rfeed. It forms a low-pass filter with a
-3dB cut off frequency .
■ Power dissipation and efficiency
Hypothesis:
• Load voltage and current are sinusoidal (Vout
and Iout)
• Supply voltage is a pure DC source (Vcc)
Regarding the load we have:
and
and
Then, the average current delivered by the supply
voltage is:
The power delivered by the supply voltage is:
Psupply = Vcc Icc
AVG
(W)
Then, the power dissipated by the amplifier is:
Pdiss = Psupply - Pout (W)
and the maximum value is obtained when:
and its value is:
Remark : This maximum value is only dependent
upon power supply voltage and load values.
)W(
R
)Vout2(
Pout
L
2
RMS
=
)V(
Rin
Rfeed
Vin1Vout −=
)V(
Rin
Rfeed
Vin21Vout2Vout =−
Rin
Rfeed
2
Vin
1Vout2Vout
Gv =
−
=
(Hz)
RinCin2
1
F
CL
π
=
)Hz(
CfeedRfeed2
1
F
CH
π
=
)V(tsinVV
PEAKOUT
ω=
)A(
R
V
I
L
OUT
OUT
=
)W(
R2
V
P
L
2
PEAK
OUT
=
)A(
R
V
2Icc
L
PEAK
AVG
π
=
)W(PP
R
Vcc22
Pdiss
OUTOUT
L
−
π
=
0
P
Pdiss
OUT
=
∂
∂
)W(
R
Vcc2
maxPdiss
L
2
2
π
=