Rainbow Electronics MAX98089 - Manual (Page 105)

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MAX98089
Low-Power, Stereo Audio Codec
with FlexSound Technology
Table 25. Power Limiter Registers
Power Limiter
The IC’s power limiter tracks the continuous power deliv-
ered 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
overheat. The result is that a loudspeaker can operate
above its rated power for a significant time before it heats
sufficiently 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.
REGISTER BIT NAME DESCRIPTION
0x44
7
PWRTH
Power Limiter Threshold
If the continuous output power from the speaker amplifiers exceeds this threshold,
the output is briefly muted to protect the speaker. The threshold is measured in watts
assuming an 8I load. VBAT must correctly reflect the voltage of SPKLVDD/SP-
KRVDD 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