SSM2166

REV. A

–3–

PIN DESCRIPTION

Pin #

Mnemonic

Function

1

GND

Ground

2

GAIN ADJUST

VCA Gain Adjust Pin. A resistor from this pin to ground sets the fixed gain of the VCA. To

check the setting of this pin the compression pin (Pin 10) should be grounded for no com-

pression. The gain can be varied from 0 dB to 20 dB. For 20 dB leave the pin open. For

0 dB of fixed gain, a typical resistor value is approximately 1 k

Ω. For 10 dB of fixed gain, the

resistor value is approximately 2 k

Ω–3 kΩ. For resistor values < 1 kΩ, the VCA can attenu-

ate or mute. Refer to Figure 6.

3

VCA Input Pin. A typical connection is a 10

µF capacitor from the buffer output pin (Pin 5)

to this pin.

4

Inverting Input to the VCA. This input can be used as a nonground reference for the audio

input signal (see application notes).

5

BUF OUT

Input Buffer Amplifier Output Pin. Must not be loaded by capacitance to ground.

6

–IN

Inverting Input to the Buffer. A 10 k

Ω feedback resistor R1 from the buffer output Pin 5 to

this input pin, and a resistor R2, from this pin through a 1

µF to ground gives gains of 6 dB

to 20 dB for R2 = 10 k

Ω to 1.1 kΩ.

7

AUDIO +IN

Input Audio Signal. The input signal should be ac-coupled (0.1

µF typical) into this pin.

8

AVG CAP

Detector Averaging Capacitor. A capacitor, 2.2

µF–22 µF, to ground from this pin is the

averaging capacitor for the detector circuit.

9

NOISE GATE SET

Noise Gate Threshold Set Point. A resistor to V+ sets the level below which input signals are

downward-expanded. For a 0.7 mV threshold, the resistor value is approximately 380 k

Ω.

Increasing the resistor value reduces the threshold. See Figure 4.

10

COMP RATIO SET

Compression Ratio Set Pin. A resistor to ground from this pin sets the compression ratio as

shown in Figure 1. Figure 5 gives resistor values for various rotation points.

11

ROTATION SET

Rotation Point Set Pin. This is set by a resistor to the positive supply. This resistor together

with the gain adjust pin determines the onset of limiting. A typical value for this resistor is

17K for a 100 mV “rotation point.” Increasing the resistor value reduces the level at which

limiting occurs. Refer to Figure 9.

12

POWER DOWN

Power-Down Pin. Connect to ground for normal operation. Connect to positive supply for

power-down mode.

13

OUTPUT

Output Signal.

14

V+

Positive Supply, +5 V Nominal.

PIN CONFIGURATION

14

13

12

11

10

9

8

1

2

3

4

7

6

5

TOP VIEW

(Not to Scale)

GND

ROTATION SET

POWER DOWN

OUTPUT

V+

GAIN ADJUST

SSM2166

AVG CAP

NOISE GATE SET

COMP RATIO SET

BUF OUT

–IN

AUDIO +IN