參數(shù)資料
型號(hào): TS4972EIJT
廠商: STMICROELECTRONICS
元件分類: 音頻/視頻放大
英文描述: 1.2 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA8
封裝: LEAD FREE, FLIP CHIP, 8 PIN
文件頁(yè)數(shù): 19/30頁(yè)
文件大?。?/td> 810K
代理商: TS4972EIJT
TS4972
Application Information
26/30
■ Note on how to use the PSRR curves
(page 7)
We have finished a design and we have chosen
the components values :
Rin=Rfeed=22k
Cin=100nF
Cb=1F
Now, on fig. 13, we can see the PSRR (input
grounded) vs frequency curves. At 217Hz we
have a PSRR value of -36dB.
In reality we want a value about -70dB. So, we
need a gain of 34dB !
Now, on fig. 12 we can see the effect of Cb on the
PSRR (input grounded) vs. frequency. With
Cb=100F, we can reach the -70dB value.
The process to obtain the final curve (Cb=100F,
Cin=100nF,
Rin=Rfeed=22k
) is a simple
transfer point by point on each frequency of the
curve on fig. 13 to the curve on fig. 12.
The measurement result is shown on the next
figure.
■ Note on PSRR measurement
What is the PSRR?
The PSRR is the Power Supply Rejection Ratio.
It's a kind of SVR in a determined frequency
range. The PSRR of a device, is the ratio between
a power supply disturbance and the result on the
output. We can say that the PSRR is the ability of
a device to minimize the impact of power supply
disturbances to the output.
How we measure the PSRR ?
■ Principle of operation
We fixed the DC voltage supply (Vcc)
We fixed the AC sinusoidal ripple voltage
(Vripple)
No bypass capacitor Cs is used
The PSRR value for each frequency is:
Remark : The measure of the Rms voltage is not a
Rms selective measure but a full range (2 Hz to
125 kHz) Rms measure. It means that we
measure the effective Rms signal + the noise.
Figure 85: PSRR changes with Cb
10
100
1000
10000
100000
-70
-60
-50
-40
-30
Cin=100nF
Cb=100
F
Cin=100nF
Cb=1
F
Vcc = 5, 3.3 & 2.6V
Rfeed = 22k, Rin = 22k
Rg = 100
, RL = 8
Tamb = 25
°C
P
S
RR
(
d
B)
Frequency (Hz)
Figure 86: PSRR measurement schematic
Vcc
Vripple
Vs-
Vs+
RL
Cb
Rfeed
Rin
Rg
100 Ohms
Cin
Bias
AV = -1
Vin-
Vin+
Bypass
Standby
VC
C
GN
D
Vout 1
Vout 2
+
-
+
-
1
3
6
8
2
5
7
4
TS4972
PSRR dB
() = 20 x Log
10
Rms Vri ppl e
()
Rms Vs + - Vs-
()
---------------------------------------------
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