TS4994IST STMicroelectronics, TS4994IST Datasheet - Page 23

• Manufacturer Part Number: TS4994IST
• Description: IC AMP AUDIO PWR 1W MONO 8MSOP
• Manufacturer: STMicroelectronics
• Type: Class ABr

Specifications of TS4994IST

• Output Type: 1-Channel (Mono)
• Max Output Power X Channels @ Load: 1W x 1 @ 8 Ohm
• Voltage - Supply: 2.5 V ~ 5.5 V
• Features: Depop, Differential Inputs, Short-Circuit and Thermal Protection, Standby
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• For Use With: 497-6396 - BOARD EVAL FOR LV TS4984IQT497-6395 - BOARD EVAL FOR LP DIFF TS4994IQT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-4452-2

TS4994
4.5
●
●
Calculating the influence of mismatching on PSRR
performance
For calculating PSRR performance, we consider that C
We 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
bypass 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
PSRR
impedance decreases to a finite value. Due to tolerance of C
in,
and the C
≤
20
×
PSRR
log
in
in
b
-------------------------------------------------------------------------------------------------------- -
(1000
feed
impedance is low to be neglected when compared to R
impedance is low enough to be neglected when
≤
= 0, the minimum PSRR would be -60dB. With a 100nF
20
impedance is high enough to be neglected as well. In
feed1
×
–
Log
Δ
in1
R
b
2
⎡
⎢
⎣
x C
x C
)
in microFarad and F in Hz) is:
(
10000
×
Δ
Δ
R
feed1
in
R
×
1
≠ R
×
100
+
−
100
F
≠ R
Δ
2
in2
R
×
in
2
feed2
x C
)
C b
⎤
⎥
⎦
and C
2
in2
(
×
dB
x C
) that will decrease the PSRR
22.2
)
feed
feed2
Application information
(
have no influence.
dB
) that will decrease the
)
feed1,2
, we
23/35
in,