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| SSM2317 Datasheet, PDF (16/20 Pages) Analog Devices – Filterless High Efficiency Mono 3 W Class-D Audio Amplifier | |||
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SSM2317
OUTPUT THRESHOLD
The maximum output amplitude threshold (VTH) during the
limiting mode can be changed from 90% to 45% of VDD by
having an external resistor, RTH, between the VTH pin and GND.
Shorting the VTH pin to GND sets VTH to 90% of VDD. Leaving
the VTH pin unconnected sets VTH to 45% of VDD. The relation
of RTH to VTH is shown by the following equation:
VTH
= 0.9 Ã
50 kΩ + RTH
50 kΩ + 2 à RTH
à VDD
Maximum output power is derived from VTH by the following
equation:
ââ VTH ââ2
POUT
=â
2â
RSP
where RSP is the speaker impedance.
Figure 43 shows the relationship between the RTH value and
VTH. Figure 44 shows the relationship between the maximum
output power and the RTH value.
100
90
80
70
60
50
40
0.1
1
10
100
1k
10k
RTH (kâ¦)
Figure 43. Output Threshold (VTH) vs. RTH
1400
1200
1000
800
600
5V (8â¦)
4.2V (8â¦)
3.6V (8â¦)
400
2.5V (8â¦)
200
0
0.1
1
10
100
1k
10k
RTH (kâ¦)
Figure 44. Maximum Output Power vs. RTH
ENABLE/DISABLING ALC
The ALC function is enabled when the ALC_EN pin is set to
VDD. The ACL function can be enabled and disabled during
amplifier operation. As a result of enabling ALC, ISY increases
by 100 μA and there is less than 50 μA source current from the
VTH pin to GND via RTH. When ALC is disabled, the source
current is 0 μA and the VTH pin is tied to GND.
Rev. A | Page 16 of 20
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