SSM3582ACPZ-R7 datasheet(33/58 Pages) AD

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Data Sheet

SSM3582A

Rev. A | Page 33 of 58

The threshold at which the output is limited is determined by

the LIM_THRES_L bits setting, Bits[7:3] in Register 0x0F for

the left channel, and the LIM_THRES_R bits setting, Bits[7:3]

in Register 0x12 for the right channel. When the ouput signal

level exceeds the set threshold level, the limiter activates and

limits the signal level to the set limit. Below the set threshold,

the output level is not affected.

The limiter threshold can be set above the maximum output

voltage of the amplifier. In this case, the limiter allows maximum

peak output. In other words, the output may clip depending on

the power supply voltage and not the limiter.

The limiter threshold can be set as fixed or to vary with the

battery voltage via the VBAT_TRACK_L bit (Register 0x0E, Bit 2)

for the left channel and VBAT_TRACK_R bit (Register 0x11,

Bit 2) for right channel. When set to fixed, the limiter threshold

is fixed and does not vary with battery voltage. The threshold

can be set from 2 V peak to 16 V peak using the LIM_THRES_x

bit (see Figure 76).

VBAT

LIM_THRES_x

LIMITER THRESHOLD FIXED AT SET VALUE

AND DOES NOT TRACK VBAT

Figure 76. Limiter Fixed (LIM_EN_x = 01, VBAT_TRACK_x = 0)

When set to a variable threshold, the SSM3582A monitors the

VBAT supply and automatically adjusts the limiter threshold

based on the VBAT supply voltage.

The VBAT supply voltage at which the limiter begins to decrease

the output level is determined by the VBAT inflection point

(the VBAT_INF _L bits (Register 0x10, Bits[7:0]) for the left

channel and VBAT_INF_R bits (Register 0x13, Bits[7:0]) for

the right channel).

The VBAT_INF_x point is defined as the battery voltage at

which the limiter either activates or deactivates depending on

the LIM_EN_x mode (see Table 22). When the battery voltage

is greater than VBAT_INF_x, the limiter is not active. When

the battery voltage is less than VBAT_INF_X, the limiter is

activated. The VBAT_INF_x bits can be set from 3.8 V to 16.2 V.

To calculate the 8-bit value for the voltage, use the following

equation:

Voltage = 3.8 + 12.4 × Decimal Value/255

Convert the decimal value to an 8-bit hexadecimal value and

use it to set the VBAT_INF_x bits.

The slope bits (Register 0x0F and Register 0x12, Bits[1:0])

determine the rate at which the limiter threshold is lowered

relative to the amount of change in VBAT below the

VBAT_INF_x point.

The slope is the ratio of the limiter threshold reduction to the

VBAT voltage reduction.

Slope = ∆Limiter Threshold/∆VBAT

The slope ratio can be set from 1:1 to 4:1. This function is

useful to prevent early shutdown under low battery conditions.

As the VBAT voltage falls, the limiter threshold is lowered. This

lower threshold results in the lower output level and therefore

helps to reduce the current drawn from the battery and in turn

helps prevent early shutdown due to low VBAT.

The limiter offers various active modes that can be set using the

LIM_EN_x bits (Register 0x0E and Register 0x11, Bits[1:0]) and

the VBAT_TRACK_x bit, as shown in Table 22.

When LIM_EN_x = 01, the limiter is enabled. When LIM_EN_x =

10, the limiter mutes the output if VBAT falls below VBAT_INF_x.

When LIM_EN_x = 11, the limiter engages only when the battery

voltage is lower than VBAT_INF_x. When VBAT is greater

than VBAT_INF_x, no limiting occurs. Note that there is

hysteresis on VBAT_INF_x for the limiter disengaging.

The limiter, when active, reduces the gain of the amplifier. The

rate of gain reduction or attack rate is determined by the

LIM_ATR_x bits (Register 0x0E and Register 0x11, Bits[5:4]).

Similarly, when the signal level drops below the limiter threshold,

the gain is restored. The gain release rate is determined by the

LIM_RRT_x bits (Register 0x0E and Register 0x11, Bits[7:6]).

INPUT LEVEL

AMPLIFIER CLIPPING LEVEL

LIM_EN_x = 00

VBAT_TRACK_x = 0 OR 1

Figure 77. Limiter Example (LIM_EN_x = 00, VBAT_TRACK_x = 0 or 1)

SSM3582ACPZ-R7 数据表(PDF) 33 Page - Analog Devices

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