TS4990 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TS4990' PDF : 33 Pages View PDF
Application information
4
Application information
TS4990
4.1
BTL configuration principle
The TS4990 is a monolithic power amplifier 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:
Pout
=
(---2----V----o---u---t-R---M---S---)--2-
RL
For the same power supply voltage, the output power in BTL configuration is four times
higher than the output power in single-ended configuration.
4.2
Gain in a typical application
The typical application schematics are shown in Figure 1 on page 4.
In the flat region (no Cin effect), the output voltage of the first stage is (in Volts):
Vout1
=
(
–Vin
)
R-----f--e---e---d-
Rin
For the second stage: Vout2 = -Vout1 (V)
The differential output voltage is (in Volts):
Vout2 – Vout1
=
2Vin
R-----f--e---e---d-
Rin
The differential gain named gain (Gv) for more convenience is:
Gv
=
V-----o---u---t-2----–-----V----o---u---t--1-
Vin
=
2
-R----f--e---e---d-
Rin
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.
4.3
Low and high frequency response
In the low frequency region, Cin starts to have an effect. Cin forms with Rin a high-pass filter
with a -3 dB cut-off frequency. FCL is in Hz.
FCL
=
-----------1-------------
2πRinCin
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 -3 dB cut-off frequency. FCH is in Hz.
FCH
=
-----------------1-------------------
2πRfeedCfeed
18/32
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