5

Application information

5.1

BTL configuration principle

The TS419 and TS421 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:

Pout (2VoutRMS)2 / RL (W)

For the same power supply voltage, the output power in BTL configuration is four times higher than the output

power in single ended configuration.

5.2

Gain in typical application schematic

In flat region (no effect of Cin), the output voltage of the first stage is:

Vout= −VinRfeedRin V

(1)

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

The differential output voltage is:

Vout2−Vout1=2VinRfeedRinV

(2)

The differential gain named gain (Gv) for more convenient usage is:

Gv= Vout2−Vout1

Vin =2RfeedRin

(3)

Remark : Vout2 is in phase with Vin and Vout1 is 180° phased with Vin. It means that the positive terminal of the

loud speaker should be connected to Vout2 and the negative to Vout1.

5.3

Low and high frequency response

In low frequency region, the effect of Cin starts. Cin with Rin forms a high pass filter with a -3 dB cut-off frequency

FCL= 12πRinCinHz

In high frequency region, you can limit the bandwidth by adding a capacitor (Cfeed) in parallel on Rfeed. Its form a

low pass filter with a -3 dB cut-off frequency.FCH= 1

2πRfeedCfeed Hz

5.4

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:

VOUT=VPEAKsinωtt

(4)

and

IOUT= VOUTRLA

(5)

TS419, TS421

Application information

DS3048 - Rev 7

page 29/42