REV. A

–8–

SSM2167

Setting the Noise Gate Threshold (Downward Expansion)

Noise gate threshold is another programmable point using an

threshold may be set between –40 dBV and –55 dBV, as shown

in Table II. The downward expansion threshold is inversely

proportional to the value of this resistance: setting this resistance

to 0

Ω sets the threshold at approximately 10 mV rms (–40 dBV),

whereas a 5 k

Ω resistance sets the threshold at approximately

1 mV rms (–55 dBV). This relationship is illustrated in Figure 5.

We do not recommend more than 5 k

the noise floor of the SSM2167 prevents the noise gate from

being lowered further without causing problems.

Table II. Setting Noise Gate Threshold

Noise Gate (dBV)

–40

0

Ω (short to V+)

–48

1 k

Ω

–54

2 k

Ω

–55

5 k

Ω

Rotation Point (Limiting)

Input signals above a particular level, “the rotation point,” are

attenuated (limited) by internal circuitry. This feature allows the

SSM2167 to limit the maximum output, preventing clipping of

the following stage, such as a CODEC or ADC. The rotation

point for SSM2167 is set internally to –24 dBV (63 mV rms) for

SSM2167-1 and –20 dBV (100 mV rms) for SSM2167-2.

Shutdown Feature

The supply current of the SSM2167 can be reduced to under 10

µA

by applying an active LOW, 0 V CMOS compatible input to the

SSM2167’s /SHUTDOWN Pin (Pin 3). In this state, the input

and output circuitry of the SSM2167 will assume a high imped-

ance state; as such, the potentials at the input pin and the output

pin will be determined by the external circuitry connected to the

SSM2167. The SSM2167 takes approximately 200 ms to settle

from a SHUTDOWN to POWER-ON command. For POWER-ON

to SHUTDOWN, the SSM2167 requires more time, typically less

than 1 s. Cycling the power supply to the SSM2167 can result in

quicker settling times: the off-to-on settling time of the SSM2167 is

less than 200 ms, while the on-to-off settling time is less than 1 ms.

The SSM2167 shutdown current is related to both temperature

and voltage.

PC Board Layout Considerations

Since the SSM2167 is capable of wide bandwidth operation and

can be configured for as much as 60 dB of gain, special care must

be exercised in the layout of the PC board that contains the IC

and its associated components. The following applications hints

should be considered for the PC board.

The layout should minimize possible capacitive feedback from

the output of the SSM2167 back to its input. Do not run input

and output traces adjacent to each other.

A single-point (“star”) ground implementation is recommended

in addition to maintaining short lead lengths and PC board runs.

In applications where an analog ground and a digital ground are

available, the SSM2167 and its surrounding circuitry should be

connected to the system’s analog ground. As a result of these

recommendations, wire-wrap board connections and grounding

implementations are to be explicitly avoided.

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

Revision History

Location

Page

Data Sheet changed from REV. 0 to REV. A.

Edits to Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Edits to Figures 2 and 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

10-Lead MSOP

(RM-10)

1

10

6

5

0.199 (5.05)

0.187 (4.75)

PIN 1

0.0197 (0.50) BSC

0.124 (3.15)

0.112 (2.84)

0.124 (3.15)

0.112 (2.84)

0.122 (3.10)

0.110 (2.79)

SEATING

PLANE

0.006 (0.15)

0.002 (0.05)

0.016 (0.41)

0.006 (0.15)

0.038 (0.97)

0.030 (0.76)

0.043 (1.09)

0.037 (0.94)

0.011 (0.28)

0.003 (0.08)

0.022 (0.56)

0.021 (0.53)

0.120 (3.05)

0.112 (2.84)

6

0