SSM2529ACBZ-R7 datasheet(21/52 Pages) AD

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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

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

0100: 5.33 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

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

10: 0.47 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

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

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.

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