TS4872_05 datasheet(21/29 Pages) STMICROELECTRONICS

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Fig. 83 : Flip Chip Demoboard Bottom Layer

■ BTL Configuration Principle

The TS4872 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

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

on 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

)

(

)

Vout

(

Pout

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 =

π Rin Cin

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

()

FCH =

π Rfeed Cfeed

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

()

VOUT = VPEAK sinωt (V)

IOUT =

VOUT

R L

----------------- (A)

POUT =

VPEAK

2RL

---------------------- (W)

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