Rainbow Electronics MAX98088 - Manual (Page 101)

Stereo Audio Codec
with FLEXSOUND Technology
MAX98088
101
Power Limiter
The IC's power limiter tracks the RMS power delivered to
the loudspeaker and briefly mutes the speaker amplifier
output if the speaker is at risk of sustaining permanent
damage.
Loudspeakers are typically damaged when the voice coil
overheats due to extended operation above the rated
power. During normal operation, heat generated in the
voice coil is transferred to the speaker’s magnet, which
transfers heat to the surrounding air. For the voice coil to
overheat, both the voice coil and the magnet must over-
heat. The result is that a loudspeaker can operate above
its rated power for a significant time before it heats suf-
ficiently to cause damage.
The IC's power limiter includes user-programmable time
constants and power thresholds to match a wide range
of loudspeakers. Program the power limiter’s threshold to
match the loudspeaker’s rated power handling. This can
be determined through measurement or the loudspeak-
er’s specification. Program time constant 1 to match the
voice coil’s thermal time constant. Program time constant
2 to match the magnet’s thermal time constant. The time
constants can be determined by plotting the voice coil’s
resistance vs. time as power is applied to the speaker.
Table 25. Power Limiter Registers
REGISTER BIT NAME DESCRIPTION
0x44
7
PWRTH
Power Limiter Threshold
If the RMS output power from the speaker amplifiers exceeds this threshold, the out-
put is briefly muted to protect the speaker. The threshold is measured in watts assum-
ing an 8I load. VBAT must correctly reflect the voltage of SPKLVDD/SPKRVDD to
achieve accurate thresholds.
6
VALUE
THRESHOLD
(W)
VALUE
THRESHOLD
(W)
0x0
Power limiter
disabled
0x8 0.27
5
0x1 0.05 0x9 0.35
0x2 0.06 0xA 0.48
0x3 0.09 0xB 0.72
0x4 0.11 0xC 1.00
4
0x5 0.13 0xD 1.43
0x6 0.18 0xE 1.57
0x7 0.22 0xF 1.80
2
PWRK
Power Limiter Weighting Factor
Determines the balance between time constant 1 and 2 to match the dominance of
each time constant in the loudspeaker.
1
VALUE T1 (%) T2 (%)
000 50 50
001 62.5 37.5
010 75 25
011 87.5 12.5
0
100 100 0
101 12.5 87.5
110 25 75
111 37.5 62.5