TS4990 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TS4990' PDF : 33 Pages View PDF
Application information
TS4990
Note:
Therefore, the power dissipated by each amplifier is:
Pdiss = Psupply - Pout (W)
Pdiss
=
2--------2----V----C----C--
π RL
Pout–Pout
and the maximum value is obtained when:
δ---P-----d---i-s---s---
δP o u t
=
0
and its value is:
Pdissmax
=
2----V----C2----C--
π2RL
(W)
This maximum value is only dependent on power supply voltage and load values.
The efficiency is the ratio between the output power and the power supply:
η=
----P-----o---u---t---
Psupply
=
--π----V----P----E---A----K-
4VCC
The maximum theoretical value is reached when VPEAK = VCC, so:
π----
4
=
78.5%
4.5
Decoupling of the circuit
Two capacitors are needed to correctly bypass the TS4990: a power supply bypass
capacitor Cs and a bias voltage bypass capacitor Cb.
Cs has particular influence on the THD+N in the high frequency region (above 7 kHz) and
an indirect influence on power supply disturbances. With a value for Cs of 1 µF, you can
expect THD+N levels similar to those shown in the datasheet.
In the high frequency region, if Cs is lower than 1 µF, it increases THD+N and disturbances
on the power supply rail are less filtered.
On the other hand, if Cs is higher than 1 µF, those disturbances on the power supply rail are
more filtered.
Cb has an influence on THD+N at lower frequencies, but its function is critical to the final
result of PSRR (with input grounded and in the lower frequency region).
If Cb is lower than 1 µF, THD+N increases at lower frequencies and PSRR worsens.
If Cb is higher than 1 µF, the benefit on THD+N at lower frequencies is small, but the benefit
to PSRR is substantial.
Note that Cin has a non-negligible effect on PSRR at lower frequencies. The lower the value
of Cin, the higher the PSRR.
20/32
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