MAX98372 Datasheet, PDF (54/91 Pages) Maxim Integrated Products – Digital Input Class D Amplifier with DHT and Brownout Protection

MAX98372
Digital Input Class D Amplifier
with DHT and Brownout Protection
MODE 2: V_PVDD is less than V_MPO, and greater than the
output voltage as set by the Rotation Point register set-
ting (V_{EXP_RP}). For example, if the RP is set for -6dBFS,
then the peak voltage on the output (V_{EXP_RP}) would
be V_MPO/2). If this is the case, the transfer function for
signals below the RP is reproduced exactly as in Mode 1.
Any signals between RP and 0dBFS are now subject to
an audio compression function, acting in the DSP block
of the MAX98372. This acts with appropriate attenuation
for peaks over the RP in magnitude with programmable
attack and release times (see the DHT Ballistics section).
Figure 9 and Figure 10 show the effect on the transfer
function.
The compression ratios in Mode 2 are effectively defined
by the combination of: PVDD, RP, SPK_GAIN_MAX, and
SPK_GAIN_MIN settings. The ballistics of the compressor
(in both Mode 2 and Mode 3) are set by the parameters
in Table 16 and Figure 21.
MODE 3a: PVDD voltage is less than the rotation points
maximum output voltage, V_{EXP_RP}. When the rotation
point is set to a high value (for example -6dBFS) this
mode applies. If V_PVDD is less than V_{EXP_RP}, then
hard limiting is applied to peaks and the effective RP is
now set by the need to fit peak signals into the available
PVDD range. The MAX98372 automatically determines
a new RP based on the PVDD ADC. Normally, RP is set
so that this mode is never used, and the V_{EXP_RP} as
set by the RP and SPK_GAIN_MAX combination should
reflect the lowest PVDD value expected. In this mode, the
SPK_GAIN_MIN parameter is set to be well below the
V_{EXP_RP}.
VMPO
VEXP_RP
SPK_GAIN_MAX
PVDD < VMPO
PEAK OUTPUT SCALED TO
FIT AVAILABLE PVDD
COMPRESSION RATIO IS SCALED TO
FIT TRANSFER FUNCTION
AUTOMATICALLY BETWEEN
ROTATION POINT AND THEORETICAL
PEAK OUTPUT VOLTAGE (AS
DETERMINED BY PVDD ADC BLOCK)
INPUT SIGNAL LEVEL (dBFS)
-6
0 _{INPUT (dBFS)}
Figure 9. Example of Dynamic Headroom Tracking in Mode 2 Operation with a High RP
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