TS4956 datasheet(36/51 Pages) STMICROELECTRONICS

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TS4956

Application information

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4.1.4

BTL output configuration (modes 1, 2, 7)

In a BTL (Bridge Tied Load) output configuration (modes 1, 2 and 4), active outputs are

biased to the VCC/2 voltage. All other inactive outputs are in the high impedance state

except for the MLO output, which is biased to VCC/2 voltage.

BTL means that each end of the load is connected to two single-ended output amplifiers.

Therefore we have:

single-ended output 1 = Vout1 = Vout (V)

single-ended output 2 = Vout2 = -Vout (V)

and

Vout1 - Vout2 = 2Vout (V)

For the same power supply voltage, the output voltage amplitude is 2 times higher than the

output voltage in the single-ended or phantom ground configurations and the output power

is 4 times higher than the output power in the single-ended or phantom ground

configurations.

4.2

Power limitation in the phantom ground configuration

A power limitation is imposed on the headphones in mode 3 and 4. Limitation of output

power is achieved by limiting the output voltage and output current on each amplifier.

The maximum value of the output voltage, Vout max, is set to a value of 1.65V in order to

reach a maximum output power of the sinusoidal signal of around 40mW per channel with a

Ω load resistance and THD+N<1%.

The maximum value of output current Iout max is set to value 70mA in order to reach a

maximum output power of the sinusoidal signal of around 40mW per channel with a 16

Ω

load resistance and THD+N<1%.

The maximum output power with these voltage and current limitations is reached with load

values more than 16

Ω and less than 32Ω as explained by Figure 125.

Figure 48 shows the functionality of the power limitation with different load resistances.

Figure 125. Voltage and current limitation on headphones

Vout

Iout

Vpeak

MAX=1.65V

Ipeak

MAX=70mA

RL=16 Ohms

RL=32 Ohms

RL=24 Ohms

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