TS4890 datasheet(36/46 Pages) STMICROELECTRONICS

36 / 46 page

Application information

TS4890

36/46

DocID8396 Rev 7

and

5.7

Power amplifier design examples

Given:

•

Load impedance: 8

Ω

•

Output power @ 1% THD+N: 0.5 W

•

Input impedance:10 k

Ω min.

•

Input voltage peak to peak: 1 Vpp

•

Bandwidth frequency: 20 Hz to 20 kHz (0, -3 dB)

•

THD+N in 20 Hz to 20 kHz < 0.5% @Pout=0.45 W

•

Ambient temperature max. = 50 °C

•

SO8 package

First of all, we must calculate the minimum power supply voltage to obtain 0.5 W into 8 W.

See curves in Figure 15, we can read 3.5 V. Thus, the power supply voltage value min. is

3.5 V. Following the maximum power dissipation equation:

with 3.5 V we have Pdissmax = 0.31 W.

Refer to power derating curves (Figure 24), with 0.31 W the maximum ambient temperature

is 100 °C. This last value could be higher if you follow the example layout shows on the

demoboard (better dissipation).

The gain of the amplifier in flat region is:

We have Rin > 10 kW. Let us take Rin = 10 k

Ω, then Rfeed = 28.25 kΩ. We could use for

Rfeed = 30 k

Ω in normalized value and the gain is G

v = 6.

In lower frequency we want 20 Hz (-3dB cut off frequency). Then:

So, we could use for CIN a 1 µF capacitor value that gives 16 Hz. In higher frequency we

want 20 kHz (-3dB cut off frequency). The Gain bandwidth product of the TS4890 is 2 MHz

typical and does not change when the amplifier delivers power into the load. The first

amplifier has a gain of:

50k

Ω C

()

Pdissmax

2Vcc

----------------- W

()

OUTPP

INPP

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

LPOUT

INPP

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

5.65

πRinF

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

795nF

TS4890 数据表(PDF) 36 Page - STMicroelectronics

TS4890 数据表(HTML) 36 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

数据表下载