TS4974 datasheet(21/25 Pages) STMICROELECTRONICS

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TS4974

Application information

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The volume is controlled by means of two pins, UP/DVC and DOWN/DVC. When the VIL

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

10k

Ω 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 430k

to 1M

Ω (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 VU/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 tdebounce 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 tautorepeat. The first period of

each autorepeat sequence is longer (tautorepeat x 1.5) to avoid any parasitic activation. In this

mode, the time trange is necessary to cover the whole gain range of the device.

Figure 42 explains the meaning of the debounce, autorepeat and range times (respectively

tdebounce, tautorepeat and trange). 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

G=+12dB

G=-33dB

Gain

(dB)

debounce

range

1.5 x t

autorepeat

Time

G=3dB

autorepeat

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