TS4994EIKJT STMICROELECTRONICS [STMicroelectronics], TS4994EIKJT Datasheet - Page 25

• Manufacturer Part Number: TS4994EIKJT
• Description: 1.2 W differential input/output audio power amplifier with selectable standby
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TS4994FC
4.5
●
●
Calculating the influence of mismatching on PSRR
performance
For calculating PSRR performance, we consider that C
use the same kind of resistor (same tolerance) and ΔR is the tolerance value in %.
The following PSRR equation is valid for frequencies ranging from DC to about 1kHz.
The PSRR equation is (ΔR in %):
This equation doesn't include the additional performance provided by bypass capacitor
filtering. If a bypass capacitor is added, it acts, together with the internal high output
impedance bias, as a low-pass filter, and the result is a quite important PSRR improvement
with a relatively small bypass capacitor.
The complete PSRR equation (ΔR in %, C
Example: With ΔR = 0.1% and C
capacitor, at 100Hz the new PSRR would be -93dB.
This example is a worst case scenario, where each resistor has extreme tolerance. It
illustrates the fact that with only a small bypass capacitor, the TS4994 provides high PSRR
performance.
Note also that this is a theoretical formula. Because the TS4994 has self-generated noise,
you should consider that the highest practical PSRR reachable is about -110dB. It is
therefore unreasonable to target a -120dB PSRR.
must introduce a mismatch factor (R
performance.
From 200Hz to 5kHz, the C
compared with R
this range, we can reach the PSRR performance of the TS4994 itself.
From 5kHz to 20kHz, the C
and the C
introduce a mismatching factor (R
PSRR performance.
feed
impedance decreases to a finite value. Due to tolerance of C
PSRR
in,
and the C
≤
20
PSRR
×
log
in
in
b
feed
impedance is low to be neglected when compared to R
impedance is low enough to be neglected when
≤
-------------------------------------------------------------------------------------------------------- -
(1000
= 0, the minimum PSRR is -60dB. With a 100nF bypass
20
impedance is high enough to be neglected as well. In
feed1
×
–
Log
in1
Δ
b
R
⎡
⎢
⎣
x C
x C
2
in microFarad and F in Hz) is:
(
10000
)
×
Δ
Δ
feed1
in
R
R
≠ R
×
×
1
−
100
100
+
≠ R
Δ
F
in2
R
2
in
2
feed2
×
x C
)
⎤
⎥
⎦
and C
C b
in2
(
2
dB
x C
×
) that will decrease the PSRR
)
22.2
feed
feed2
Application information
have no influence. We
(
) that will decrease the
dB
)
feed1,2
, we
25/35
in,