TS2007_11 Datasheet, PDF (23/29 Pages) STMicroelectronics – 3 W filter-free Class D audio power amplifer with 6-12 dB fixed gain select

TS2007
Application information
4.5
4.6
Note:
F_CL
=
-----------------¹------------------
2 ⋅ π ⋅ Z_in ⋅ C_in
So, for a desired cutoff frequency F_CL we can calculate C_in:
C_in = -₂----_â‹---_π-----_â‹---_Z--¹--_i-_n-----_â‹--_F----_C----_L-
with F_CL in Hz, Z_in in Ω and C_in in F.
The input impedance Z_in is for the whole power supply voltage range, typically 75 kΩ . There
is also a tolerance around the typical value (see Table 5 to Table 9). With regard to the
tolerance, you can also calculate tolerance of F_CL:
● F_CLmax = 1.103 ⋅ F_CL
● F_CLmin = 0.915 ⋅ F_CL
Decoupling of the circuit
A power supply capacitor, referred to as C_S, is needed to correctly bypass the TS2007.
The TS2007 has a typical switching frequency of 280 kHz and output fall and rise time of
about 5 ns. Due to these very fast transients, careful decoupling is mandatory.
A 1 µF ceramic capacitor is enough, but it must be located very close to the TS2007 in order
to avoid any extra parasitic inductance created by a long track wire. Parasitic loop
inductance, in relation with di/dt, introduces overvoltage that decreases the global efficiency
of the device and may cause, if this parasitic inductance is too high, a TS2007 breakdown.
In addition, even if a ceramic capacitor has an adequate high frequency ESR value, its
current capability is also important. A 0603 size is a good compromise, particularly when a
4 Ω load is used.
Another important parameter is the rated voltage of the capacitor. A 1µF/6.3V capacitor
used at 5 V, loses about 50% of its value. With a power supply voltage of 5 V, the decoupling
value, instead of 1 µF, could be reduced to 0.5 µF. As C_S has particular influence on the
THD+N in the medium to high frequency region, this capacitor variation becomes decisive.
In addition, less decoupling means higher overshoots which can be problematic if they reach
the power supply AMR value (6 V).
Wake-up time (t_wu)
When the standby is released to set the device ON, there is a wait of 5 ms typically. The
TS2007 has an internal digital delay that mutes the outputs and releases them after this
time in order to avoid any pop noise.
The gain increases smoothly (see Figure 49) from the mute to the gain selected by the GS
pin (Section 4.2).
Doc ID 13123 Rev 4
23/29