8

FN6788.0

September 29, 2008

This terminal allows to set up the threshold level of audio

input to be detected. When audio input to either Left or Right

channel is below this threshold - the FLAG output is Low;

when audio input is above this threshold - the FLAG output

is High. The threshold level is maintained over an external

±10µA current, and VB pin. To calculate the actual threshold

we need to multiply 10µA by a resistor value and divide the

result by 1000. For example, a 100k

Ω resistor is a subject of

1mV audio detection threshold, e.g. 10µA*100k/1000 = 1mV.

1/2 of AVCC. The maximum resistor value for detection

threshold can be found in Table 2.

Device Operation

There are four sections in the ISL22102: the input control,

counter and decode section, two resistor arrays with

buffered wiper outputs, reference voltage generator of VB

output, and audio detection block with programmable delay

FLAG output. The input control section operates just like an

up/down counter. The output of this counter is decoded to

turn on a single electronic switch, connecting a point on the

resistor array to the wiper output. Each resistor array is

comprised of 31 individual resistors connected in series and

its wiper output pass an attenuated audio input to the power

amplifier. Both resistor arrays have logarithmic taper with

-72dB dynamic range as shown in Table 2.

The ISL22102 is designed to interface directly to two

push-button switches for effectively moving the wipers up or

down. The UP and DN inputs increment or decrement 5-bit

counters respectively. The output of these counters are

decoded to select one of the thirty-two wiper positions along

the resistive array. The wiper increment input, UP, and the

wiper decrement input, DN, are both connected to an

internal pull-up so that they normally remain High. When

pulled Low by an external push button switch or a logic Low

level input, the wipers will be switched to the next adjacent

tap position.

Internal debounce circuitry prevents inadvertent switching of

the wipers position if UP or DN remain Low for less than

15ms, typical. Each of the buttons can be pushed either

once for a single increment/decrement or continuously for a

multiple increments/decrements. When making a continuous

push, after the first second, the device is going to auto

increment/decrement mode. If the button is held for longer

than 1s, the wiper position will be auto

increment/decremented with rate of 4Hz for 4s, and with rate

of 8Hz after that. As soon as the button is released, the

ISL22102 will return to a low power standby condition.

Each wiper acts like its mechanical equivalent and does not

move beyond the last position. That is, the counter does not

wrap around when clocked to either extreme.

Table 3 contains information about attenuation level for each

tap position.

AVCC (V)

5.5

188

5.25

177

5.0

167

4.75

156

4.5

146

4.25

135

4.0

125

3.75

115

3.5

104

3.25

94

3.0

83

2.75

73

TABLE 3. WIPER TAP POSITION vs ATTENUATION

TAP POSITION

ATTENUATION

00

1-2dB

2-4dB

3-6dB

4-8dB

5

-10dB

6

-12dB

7

-14dB

8

-16dB

9

-18dB

10

-20dB

11

-22dB

12

-24dB

13

-26dB

14

-28dB

15

-30dB

16

-32dB

17

-34dB

18

-36dB

19

-38dB

20

-40dB

21

-42dB

22

-44dB

23

-46dB

24

-48dB

25

-50dB

26

-52dB

ISL22102