Application information

TS4990

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DocID9309 Rev 14

4

Application information

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:

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):

For the second stage: Vout2 = -Vout1 (V)

The differential output voltage is (in Volts):

The differential gain named gain (Gv) for more convenience is:

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.

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.

P

out

2V

out

RMS



2

R

L

------------------------------

=

V

out1

V

–

in



R

feed

R

in

--------------

=

V

out2

V

out1

–

2V

in

R

feed

R

in

--------------

=

G

v

V

out2

V

out1

–

V

in

----------------------------------

2

R

feed

R

in

--------------

==

F

CL

1

2

R

inCin

------------------------

=

F

CH

1

2

R

feedCfeed

-------------------------------------

=