SSM3582BCPZ datasheet(33/59 Pages) AD

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Data Sheet

SSM3582

Rev. 0| Page 33 of 59

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 77).

When set to a variable threshold, the SSM3582 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. The 8-bit

value for the voltage can be calculated using 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 = ΔLimiter Threshold/ΔVBAT

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 bits

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

INPUT LEVEL

AMPLIFIER CLIPPING LEVEL

LIM_EN_x = 00

VBAT_TRACK_x = 0

Figure 76. Limiter Example (LIM_EN_x = 0b0, VBAT_TRACK_x = 0bX)

VBAT

LIM_THRES_x

LIMITER THRESHOLD FIXED AT SET VALUE

AND DOES NOT TRACK VBAT

Figure 77. Limiter Fixed (LIM_EN_x = 0b01, VBAT_TRACK_x = 0b0)

Table 22. Limiter Modes

LIM_EN_x

VBAT_TRACK_x

Limiter

VBAT < VBAT_INF_x

VBAT > VBAT_INF_x

Comments

0 or 1

Not applicable

See Figure 76

Fixed

Use the set threshold

See Figure 77

Variable

Lowers the threshold

Use the set threshold

See Figure 78 and Figure 79

0 or 1

Fixed

Mutes the output

Use the set threshold

Not shown

Fixed

Use the set threshold

No limiting

See Figure 80 and Figure 81

Variable

Lowers the threshold

No limiting

See Figure 82 and Figure 83

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