TS4890IST View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

TS4890IST

RAIL TO RAIL OUTPUT 1W AUDIO POWER AMPLIFIER WITH STANDBY MODE ACTIVE LOW

STMicroelectronics 

TS4890

s Power amplifier design examples

Given :

• Load impedance : 8Ω

• Output power @ 1% THD+N : 0.5W

• Input impedance : 10kΩ min.

• Input voltage peak to peak : 1Vpp

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

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

• Ambient temperature max = 50°C

• SO8 package

First of all, we must calculate the minimum power

supply voltage to obtain 0.5W into 8Ω. See curves

in fig. 15, we can read 3.5V. Thus, the power

supply voltage value min. will be 3.5V.

Following the maximum power dissipation

equation :

Pdiss max

=

2 Vcc2

π2RL

(W)

with 3.5V we have Pdissmax=0.31W.

Refer to power derating curves (fig. 24), with

0.31W the maximum ambient temperature will be

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 will be :

GV

=

VOUTPP

VINPP

=

2

2RLPOUT

VINPP

= 5.65

We have Rin > 10kΩ. Let's take Rin = 10kΩ, then

Rfeed = 28.25kΩ. We could use for Rfeed = 30kΩ

in normalized value and the gain will be Gv = 6.

In lower frequency we want 20 Hz (-3dB cut off

frequency). Then

CIN

=

1

2π Rin FCL

= 795nF

So, we could use for Cin a 1µF capacitor value that

gives 16Hz.

In Higher frequency we want 20kHz (-3dB cut off

frequency). The Gain Bandwidth Product of the

TS4890 is 2MHz typical and doesn't change when

the amplifier delivers power into the load.

The first amplifier has a gain of

Rfeed = 3

Rin

and the theoretical value of the -3dB cut of higher

frequency is 2MHz/3 = 660kHz.

We can keep this value or limiting the bandwidth

by adding a capacitor Cfeed, in parallel on Rfeed.

Then

CFEED

=

1

2π RFEED

FCH

= 265pF

So, we could use for Cfeed a 220pF capacitor

value that gives 24kHz.

Now, we can choose the value of Cb with the

constraint THD+N in 20Hz to 20kHz < 0.5% @

Pout=0.45W. If you refer to the closest THD+N vs

frequency measurement : fig. 71 (Vcc=3.3V,

Gv=10), with Cb = 1µF, the THD+N vs frequency

is always below 0.4%. As the behaviour is the

same with Vcc = 5V (fig. 67), Vcc = 2.6V (fig. 67).

As the gain for these measurements is higher

(worst case), we can consider with Cb = 1µF, Vcc

= 3.5V and Gv = 6, that the THD+N in 20Hz to

20kHz range with Pout = 0.45W will be lower than

0.4%.

In the following tables, you could find three

another examples with values required for the

demoboard.

Remark : components with (*) marking are

optional.

Application n°1 : 20Hz to 20kHz bandwidth and

6dB gain BTL power amplifier.

Components :

Designator

Part Type

R1

22k / 0.125W

R4

22k / 0.125W

R6

Short Cicuit

R7*

(Vcc-Vf_led)/If_led

R8

10k / 0.125W

C5

470nF

C6

100µF

26/32

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