Data Sheet SSM2529
Rev. 0 | Page 21 of 52
DRC Hold Time
Two types of hold time are used in the DRC. One is used in normal
mode to prevent the calculated gain from increasing too quickly,
and the other is used during DRC transiting from expander
mode to noise gating mode to prevent the DRC from entering
noise gating too quickly. The DRCHTNOR and DRCHTNG bits
in Register 0x5E set which type is used.
Table 35. DRC_HOLD_TIME Register
D7 D6 D5 D4 D3 D2 D1 D0
DRCHTNG[3:0] DRCHTNOR[3:0]
Table 36. Bit Description of DRC_HOLD_TIME Register
Bit Name Description Settings
DRCHTNG[3:0] DRC hold time for
noise gating
0000: 0 ms
0001: 0.67 ms
xxxx: double time
0111: 42.67 ms (default)
1111: 43.7 sec
DRCHTNOR[3:0] DRC hold time for
normal operation
0000: 0 ms
0001: 0.67 ms
0010: 1.33 ms
0011: 2.67 ms
1111: 43.7 sec
GAIN RIPPLE REMOVE
Due to the swing of the peak/rms value detected by the level
measurement, the gain to apply to the input signal has a little
ripple, which leads to the modulation of the output signal. The
ripple remove function suppresses this effect. The ripple
threshold is defined by the DRCRRH bit in Register 0x5F.
Table 37. DRC_RIPPLE_CTRL Register
D7 D6 D5 D4 D3 D2 D1 D0
Reserved DRCRRH[1:0]
Table 38. Bit Description of DRC_RIPPLE_CTRL Register
Bit Name Description Settings
DRCRRH[1:0] DRC ripple
remove threshold
00: 0 dB
01: 0.28 dB
11: 0.75 dB (default)
SPEAKER PROTECTION
The IC includes a speaker temperature prediction module to
protect the loudspeaker. Loudspeakers can be damaged when the
voice coil overheats due to operation higher than the rated
power. Typically, the thermal time constants of the loudspeakers
are long, approximately 1 sec for voice coil and 60 sec for core.
They can handle momentary power spikes without overheating;
however, they cannot handle sustained high power. The speaker
protection method used in the IC can reduce the volume when
the temperature of the loudspeaker exceeds the temperature
threshold set by the user while preserving the maximum power
of the loudspeaker. The temperature prediction method is based
on the general thermal model of the loudspeaker.
In this thermal model, R1, R2, C1, and C2 are temperature
coefficients derived by measuring loudspeaker characteristics.
They are set by the I2C control registers, Register 0x84 to
Register 0x8B (SP_CF1_H, SP_CF1_L, SP_CF2_H, SP_CF2_L,
SP_CF3_H, SP_CF3_L, SP_CF4_H and SP_CF4_L).
Other critical parameters needed include ambient temperature,
dc resistance of the loudspeaker, and temperature coefficient of
the voice coil material. These parameters are set by Register 0x81 to
Register 0x83 (TEMP_AMBIENT, SPKR_DCR, and SPKR_TC).
After running the thermal model by setting the speaker protection
enable bit (SP_EN, Register 0x80), the speaker voice coil temperature
status and speaker magnet temperature status can be obtained
by an I2C reading of the SPKR_TEMP register (Register 0x8C)
and the SPKR_TEMP_MAG register (Register 0x8D). The user
sets the voice coil temperature threshold (maximum speaker
voice coil temperature before gain reduction occurs) by using
the MAX_SPKR_TEMP register (Register 0x8E). If this threshold
is crossed, the output volume is reduced according to the speed
set by the SP_AR bits (speaker protection gain reduction attack
rate, Register 0x8F, Bits[7:4]) and the SP_RR bits (speaker
protection gain reduction release rate, Register 0x8F, Bits[3:0]).
POWER SUPPLIES
The SSM2529 has two internal power supplies that must be
provided: SPKVDD and DVDD. The SPKVDD supply powers
to the full bridge power stage of the MOSFET and its associated
drive, control, and protection circuitry. SPKVDD can operate
from 2.5 V to 5.5 V and must be present to obtain audio output.
Lowering the SPKVDD supply results in lower output power
and correspondingly lower power consumption, and it does not
affect audio performance.
DVDD provides power to the digital logic and analog components.
DVDD can operate from 1.08 V to 1.98 V, and it must be provided
to write to the I2C or to obtain audio output. Lowering the supply
voltage results in lower power consumption; however, it also
results in lower audio performance.
POWER CONTROL
The SSM2529 includes various programmable power-down modes
that are contained in the first I2C register (Register 0x00), power/
reset control. By default, the IC is set in software power-down,
which is the I2C programmable master power-down. Only I2C
functionality operates when in software power-down mode.
The SSM2529 also contains a smart power-down feature that,
when enabled, looks at the incoming digital audio. In addition,
if the audio is zero for 1024 consecutive samples, regardless of
sample rate, it puts the IC in a smart power-down state. In this
state, all circuitry, except the I2S and I2C ports, are placed in a
low power state. After a single nonzero input is received, the
SSM2529 leaves this state and resumes normal operation.