Obsolete
Product(s)
- Obsolete
Product(s)
TS4900
15/19
N
O
T
F
O
R
NEW
D
ES
IG
N
■ BTL Configuration Principle
The TS4900 is a monolithic power amplifier with a
BTL (Bridge Tied Load) output configuration. BTL
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 1)
In flat region (no effect of Cin), 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
180 phased with Vin. It means that the positive
terminal of the loudspeaker should be connected
to Vout2 and the negative to Vout1.
■ Low and high frequency response
In low frequency region, the effect of Cin starts.
Cin with Rin forms a high pass filter with a -3dB cut
off frequency
In high frequency region, you can limit the
bandwidth by adding a capacitor (Cfeed) in parallel
with Rfeed. Its form a low pass filter with a -3dB cut
off frequency
■ Power dissipation and efficiency
Hypothesis :
Voltage and current in the load are sinusoidal
(Vout and Iout)
Supply voltage is a pure DC source (Vcc)
Regarding the load we have:
and
Then, the average current delivered by the supply
voltage is:
The power delivered by the supply voltage is
Psupply = Vcc IccAVG (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 depending
on power supply voltage and load values.
The efficiency is the ratio between the output
)
W
(
R
)
Vout
2
(
Pout
L
2
RMS
=
Vout1 =
Vin
–
R fe ed
Ri n
-------------------- (V)
Vout2
Vo ut1 = 2Vin
–
Rfee d
Rin
-------------------- (V)
Gv =
Vout2
Vou t1
–
Vi n
--------------------------------------- = 2
Rfee d
Ri n
--------------------
F CL =
1
2
π Rin Cin
--------------------------------
Hz
()
FCH =
1
2
π Rfeed Cfeed
-----------------------------------------------
Hz
()
VOUT = VPEAK sinωt (V)
IOUT =
VOUT
R L
----------------- (A)
POUT =
VPEAK
2
2RL
---------------------- (W)
ICC
AVG
= 2
VPEAK
πRL
-------------------- (A)
Pdi ss =
22 Vcc
π RL
---------------------- POUT
POUT (W)
–
Pdiss
POUT
---------------------- = 0
)
W
(
R
Vcc
2
max
Pdiss
L
2
π
=