Datasheet

LMV1089
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010 www.ti.com
SHUTDOWN VIA I
2
C
The LMV1089 offers an additional shutdown function by reprogramming an I
2
C register (see Table 5). The
LMV1089 will only consume power in a mode where it can perform its normal functions. So at least one of the
microphone amplifier circuits must be enabled ('1'). Writing '0' to the both bit 4 and bit 5 of the I
2
C 'A' register
(address 0x01h) of the LMV1089 will force the part into shutdown mode, even if the EN pin is 'High', the only part
that remains active in this state is the I
2
C, which consumes neglectible power when compared to the standby
current.
Adjustable Gain
The LMV1089 has two gain stages where the gain can be adjusted to meet the requirements for the application.
There is a preamplifier and a post amplifier that can be varied independent of each other. In most applications
the gain will be set via the I
2
C interface, see Table 5.
SETTING ADJUSTABLE GAIN
The LMV1089 provides four pins to set the default gain settings during power up of the device, which is
convenient for applications without a micro controller . The default gain of the preamplifier is controlled by the
GA0 and GA1 pins and can be set by wiring those pins to either V
DD
or GND. In this way, one of the four
possible values in the 12dB to 36dB range (see Table 1) can be chosen. The default post amplifier gain is set in
the same way by connecting the GB0 and GB1 pins to either V
DD
or GND to select a gain between 6dB and
15dB (see Table 2). Setting the gain of the preamplifier and post amplifier via the I
2
C interface (see Table 5) will
override this default gain.
The default gain is only set during power up of the device. Toggling the logic level of the enable pin (EN) will not
change the current gain setting of the part. Any gain setting done via the I
2
C interface will remain valid during
activation of the function.
Table 1. Default preamplifier gain
GA1 GA0 Gain
0 0 12dB
0 1 20dB
(1)
1 0 28dB
1 1 36dB
(1) Default value used for performance measurements
Table 2. Default post amplifier gain
GB1 GB0 Gain
0 0 6dB
(1)
0 1 9dB
1 0 12dB
1 1 15dB
(1) Default value used for performance measurements
Gain Balance and Gain Budget
In systems where input signals have a high dynamic range, critical noise levels or where the dynamic range of
the output voltage is also limited, careful gain balancing is essential for the best performance. Too low of a gain
setting in the preamplifier can result in higher noise levels while too high of a gain setting in the preamplifier will
result in clipping and saturation in the noise cancelling processor and output stages.
The gain ranges and maximum signal levels for the different functional blocks are shown in Figure 22. Two
examples are given as a guideline on how to select proper gain settings.
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