TS4974_07 Datasheet, PDF (21/25 Pages) STMicroelectronics – 1W differential audio power amplifier with up/down digital volume control pins

TS4974
Application information
The volume is controlled by means of two pins, UP/DVC and DOWN/DVC. When the V_IL
voltage is applied, it activates the increase or decrease in gain. When one of the input pins
is grounded, volume changing is activated. When both volume UP and DOWN functions are
activated at the same time, there is no effect on the volume.
The UP/DVC and DOWN/DVC inputs need to be pulled-up or pulled-down, so a pair of
external pull-up or pull-down resistors are required. When pull-up resistors are used, it is
dependent on the application which values of resistors you should choose in the range from
10kΩ to 1MΩ. The current flowing through the switch S1 or S2 during volume changing is
adjusted by the value of the pull-up resistors.
When pull-down resistors are used, the values are chosen in the range from at least 430kΩ
to 1MΩ (a value 470kΩ is recommended). Typically, in this case a 10µA current flows through
the switch S1 or S2 during volume changing.
Table 2 on page 3 indicates the values of the V_U/D voltages required to activate an increase
or decrease in volume. The volume can also be controlled by a microcontroller. In this case,
transistors can be used as switches for grounding the UP/DVC and DOWN/DVC pins.
The TS4974 integrates a debouncing system which does not take into account UP or
DOWN pulses that are shorter than the t_debounce time. In addition, an autorepeat function is
implemented. When a continuous voltage is applied to the UP or DOWN pin, the gain is
continuously increased or decreased after a certain time called t_autorepeat. The first period of
each autorepeat sequence is longer (t_autorepeat x 1.5) to avoid any parasitic activation. In this
mode, the time t_range is necessary to cover the whole gain range of the device.
Figure 42 explains the meaning of the debounce, autorepeat and range times (respectively
t_debounce, t_autorepeat and t_range). It shows how the volume increases over the whole volume
range from the minimum gain -33 dB to the maximum gain +12 dB by 3 dB steps.
Figure 42. Example of volume change
Gain
(dB)
t_autorepeat
G=+12dB
1.5 x t_autorepeat
G=3dB
G=-33dB
V_UP
Time
t_debounce
t_range
Time
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