TS4974_07 Datasheet, PDF (22/25 Pages) STMicroelectronics – 1W differential audio power amplifier with up/down digital volume control pins

Application information
TS4974
4.10
Notes on PSRR measurement
What is the PSRR?
The PSRR is the power supply rejection ratio. The PSRR of a device is the ratio between a
power supply disturbance and the result on the output. In other words, the PSRR is the
ability of a device to minimize the impact of power supply disturbance to the output.
How is the PSRR measured?
The PSRR is measured as shown in Figure 43.
Figure 43. PSRR measurement
VCC VCC
Volume DOWN _S1
Rpu1
470k
Rpu2
470k
Volume UP
S2
Rpd1 Rpd1
470k 470k
U1
Vripple
Vcc
DIGITAL VOLUME
CONTROL
Cin1
10 Ohms
330nF
Cin2
330nF
10 Ohms
1 Vin-
2 Vin+
3 BYP ASS
BIAS
Vout- 9
+
Vout+ 8
Cb
1µF
STBY
TS4974 DFN10
STBY
STBY control
Principles of operation
● The DC voltage supply (V_CC) is fixed
● The AC sinusoidal ripple voltage (V_ripple) is fixed
● No bypasss capacitor Cs is used
The PSRR value for each frequency is calculated as:
PSRR = 20 × Log _-^R_-----^M_-----^S_----⁽_--^O_----^u_---^t_--^p_---^u_---^t_-⁾_- (dB)
RMS_(Vripple)
RMS is an rms selective measurement.
RL
8 Ohms
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