Datasheet

LM4938
SNAS245B –FEBRUARY 2005–REVISED MAY 2013 www.ti.com
DC VOLUME CONTROL
The LM4938 has an internal stereo volume control whose setting is a function of the DC voltage applied to the
DC VOL CONTROL pin.
The LM4938 volume control consists of 31 steps that are individually selected by a variable DC voltage level on
the volume control pin. The range of the steps, controlled by the DC voltage, are from 0dB - 89dB. Each gain
step corresponds to a specific input voltage range, as shown in VOLUME CONTROL TABLE.
To minimize the effect of noise on the volume control pin, which can affect the selected gain level, hysteresis has
been implemented. The amount of hysteresis corresponds to half of the step width, as shown in Volume Control
Characterization Graph (DS200133-40).
For highest accuracy, the voltage shown in the 'recommended voltage' column of the table is used to select a
desired gain. This recommended voltage is exactly halfway between the two nearest transitions to the next
highest or next lowest gain levels.
The gain levels are 1dB/step from 0dB to -6dB, 2dB/step from -6dB to -36dB, 3dB/step from -36dB to -47dB,
4dB/step from -47db to -51dB, 5dB/step from -51dB to -66dB, and 12dB to the last step at -89dB.
VOLUME CONTROL TABLE
Gain (dB) Voltage Range (% of Vdd) Voltage Range (Vdd = 5) Voltage Range (Vdd = 3)
Low High Recommended Low High Recommended Low High Recommended
0 77.5% 100.00% 100.000% 3.875 5.000 5.000 2.325 3.000 3.000
-1 75.0% 78.5% 76.875% 3.750 3.938 3.844 2.250 2.363 2.306
-2 72.5% 76.25% 74.375% 3.625 3.813 3.719 2.175 2.288 2.231
-3 70.0% 73.75% 71.875% 3.500 3.688 3.594 2.100 2.213 2.156
-4 67.5% 71.25% 69.375% 3.375 3.563 3.469 2.025 2.138 2.081
-5 65.0% 68.75% 66.875% 3.250 3.438 3.344 1.950 2.063 2.006
-6 62.5% 66.25% 64.375% 3.125 3.313 3.219 1.875 1.988 1.931
-8 60.0% 63.75% 61.875% 3.000 3.188 3.094 1.800 1.913 1.856
-10 57.5% 61.25% 59.375% 2.875 3.063 2.969 1.725 1.838 1.781
-12 55.0% 58.75% 56.875% 2.750 2.938 2.844 1.650 1.763 1.706
-14 52.5% 56.25% 54.375% 2.625 2.813 2.719 1.575 1.688 1.631
-16 50.0% 53.75% 51.875% 2.500 2.688 2.594 1.500 1.613 1.556
-18 47.5% 51.25% 49.375% 2.375 2.563 2.469 1.425 1.538 1.481
-20 45.0% 48.75% 46.875% 2.250 2.438 2.344 1.350 1.463 1.406
-22 42.5% 46.25% 44.375% 2.125 2.313 2.219 1.275 1.388 1.331
-24 40.0% 43.75% 41.875% 2.000 2.188 2.094 1.200 1.313 1.256
-26 37.5% 41.25% 39.375% 1.875 2.063 1.969 1.125 1.238 1.181
-28 35.0% 38.75% 36.875% 1.750 1.938 1.844 1.050 1.163 1.106
-30 32.5% 36.25% 34.375% 1.625 1.813 1.719 0.975 1.088 1.031
-32 30.0% 33.75% 31.875% 1.500 1.688 1.594 0.900 1.013 0.956
-34 27.5% 31.25% 29.375% 1.375 1.563 1.469 0.825 0.937 0.881
-36 25.0% 28.75% 26.875% 1.250 1.438 1.344 0.750 0.862 0.806
-39 22.5% 26.25% 24.375% 1.125 1.313 1.219 0.675 0.787 0.731
-42 20.0% 23.75% 21.875% 1.000 1.188 1.094 0.600 0.712 0.656
-45 17.5% 21.25% 19.375% 0.875 1.063 0.969 0.525 0.637 0.581
-47 15.0% 18.75% 16.875% 0.750 0.937 0.844 0.450 0.562 0.506
-51 12.5% 16.25% 14.375% 0.625 0.812 0.719 0.375 0.487 0.431
-56.5 10.0% 13.75% 11.875% 0.500 0.687 0.594 0.300 0.412 0.356
-62.5 7.5% 11.25% 9.375% 0.375 0.562 0.469 0.225 0.337 0.281
-68.5 5.0% 8.75% 6.875% 0.250 0.437 0.344 0.150 0.262 0.206
-89 0.0% 6.25% 0.000% 0.000 0.312 0.000 0.000 0.187 0.000
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