TS472_06 Datasheet, PDF (16/24 Pages) STMicroelectronics – Very low noise microphone preamplifier with 2.0V bias output and active low standby mode

Application information
TS472
5.5
Gain settings
The gain in the application depends mainly on:
● the sensitivity of the microphone
● the distance to the microphone
● the audio level of the sound
● the desired output level
The sensitivity of the microphone is generally expressed in dB/Pa, referenced to 1V/Pa. For
example, the microphone used in testing had an output voltage of 6.3mV for a sound
pressure of 1 Pa (where Pa is the pressure unit, Pascal). Expressed in dB, the sensitivity is:
20Log(0.0063) = -44 dB/Pa
To facilitate the first approach, Table 11 below gives voltages and gains used with a low cost
omnidirectional electret condenser microphone of -44dB/Pa.
Table 11. Typical TS472 gain vs. distance to the microphone (sensitivity -44dB/Pa)
Distance to microphone Microphone output voltage
TS472 Gain
1cm
20cm
30mV_RMS
20
3mV_RMS
100
The gain of the TS472 microphone preamplifier can be set:
1. From -1.5 dB to 41 dB by connecting an external grounded resistor R_GS to the GS pin.
It allows to adapt more precisely the gain to each application.
Table 12. Selected gain vs. gain select resistor
Gain (dB)
0
10
20
30
40
R_GS (Ω)
470k
27k
4k7
1k
68
Figure 35. Gain in dB vs. gain select resistor Figure 36. Gain in V/V vs. gain select resistor
50
Tamb=25°C
40
30
20
10
0
-10
10
100
1k
10k
100k
1M
R (Ω)
GS
Tamb=25°C
100
10
1
10
100
1k
10k
100k
1M
R (Ω)
GS
2. To 20dB by applying V_GS > 1V_DC on Gain Select (GS) pin. This setting can help to
reduce a number of external components in an application, because 2.0 V_DC is
provided by TS472 itself on BIAS pin.
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