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参数资料
| 型号： | TS4902IST |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.7 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8 |
| 封装： | MINI, PLASTIC, SO-8 |
| 文件页数： | 9/19页 |
| 文件大小： | 404K |
| 代理商： | TS4902IST |
TS4902
17/19
At power OFF of the supply, Cs is discharged by a
constant current Icc. The discharge time from 5V
to 0V of Cs is
Now, we must consider the discharge time of Cb.
At power OFF or standby ON, Cb is discharged by
a 100k
resistor. So the discharge time is about
τb
Disch ≈ 3xCbx100k (s).
In the majority of application, Cb=1F, then
τb
Disch≈300ms >> tdischCs.
s 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 fact, we want a value of 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 figure A.
Fig. A : PSRR changes with Cb
s Remark on PSRR measurement conditions
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 the
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 do we measure the PSRR ?
Fig. B : PSRR measurement schematic
s Measurement process:
Fix the DC voltage supply (Vcc)
Fix the AC sinusoidal ripple voltage (Vripple)
No bypass capacitor Cs is used
The PSRR value for each frequency is :
Remark
: The measurement of the RMS voltage is
not a selective RMS measurement but a full range
(2 Hz to 125 kHz) RMS measurement. This means
we have: the effective RMS signal + the noise.
tDischCs =
5Cs
Icc
-------------- = 83 ms
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
PSR
R
(dB
)
Frequency (Hz)
Vripple
Vcc
Rin
Cin
Rg
100 Ohms
Cb
Rfeed
4
3
2
1
5
8
Vin-
Vin+
-
+
-
+
Bypass
Standby
Bias
6
Vout1
Vout2
Av=-1
TS4902
Vs-
Vs+
RL
Vcc
GND
7
PSRR d B
() = 20 x Log
10
Rm s Vrippl e
()
Rm s Vs + - Vs-
()
---------------------------------------------
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