TS4890 ST Microelectronics, Inc., TS4890 Datasheet - Page 26

• Manufacturer Part Number: TS4890
• Description: 1W Mono Audio Amplifier With Standby Active High
• Manufacturer: ST Microelectronics, Inc.

TS4890
Given :
• Load impedance : 8
• Output power @ 1% THD+N : 0.5W
• Input impedance : 10k
• 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 8 . See curves
in fig. 15, we can read 3.5V. Thus, the power
supply voltage value min. will be 3.5V.
Following
equation :
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 :
We have Rin > 10k . Let's take Rin = 10k , then
Rfeed = 28.25k . We could use for Rfeed = 30k
in normalized value and the gain will be Gv = 6.
In lower frequency we want 20 Hz (-3dB cut off
frequency). Then
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.
26/32
Power amplifier design examples
G
V
the
C
Pdiss
V
IN
V
OUTPP
INPP
maximum
2
max
Rin
1
2
F
2
min.
CL
2
V
Vcc
R
2
INPP
R
L
P
power
L
2
795
OUT
(
W
nF
)
. 5
dissipation
65
The first amplifier has a gain of
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
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 :
R1
R4
R6
R7*
R8
C5
C6
Designator
C
FEED
2
Rfeed
R
Rin
FEED
1
22k / 0.125W
22k / 0.125W
Short Cicuit
(Vcc-Vf_led)/If_led
10k / 0.125W
470nF
100µF
F
3
CH
Part Type
265
pF