LMV1089RLEVAL National Semiconductor, LMV1089RLEVAL Datasheet - Page 15

• Manufacturer Part Number: LMV1089RLEVAL
• Description: BOARD EVALUATION LMV1089
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LMV1089RLEVAL

• Main Purpose: Audio, Microphone Amp
• Embedded: No
• Utilized Ic / Part: LMV1089
• Primary Attributes: Dual Input, Single Output
• Secondary Attributes: Graphical User Interface, I²C Interface
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Data
INTRODUCTION
The LMV1089 is a fully analog single chip solution to reduce
the far field noise picked up by microphones in a communi-
The output signal of the microphones is first amplified by a
pre-amplifier stage with an adjustable gain of 6dB to 36dB.
The signal is then processed by the noise cancelling proces-
sor. The noise cancelling processor matches the gain and
frequency responses of the microphones and the acoustic
characteristics of the enclosure using coefficients derived
during the auto-calibration step and the stored in EEPROM.
The resulting noise-suppressed signal is then amplified by the
6dB to 18dB gain-adjustable post-amplifier. For optimum
noise and EMI immunity, the microphones have a differential
connection to the LMV1089 and the output of the LMV1089
is also differential. The adjustable gain functions can be con-
trolled via I
scribed later in the application section.
Power Supply Circuits
A low drop-out (LDO) voltage regulator in the LMV1089 allows
the device to be independent of supply voltage variations.
The Power On Reset (POR) circuitry in the LMV1089 requires
the supply voltage to rise from 0V to V
The Mic Bias output is provided as a low noise supply source
for the electret microphones. The noise voltage on the Mic
Bias microphone supply output pin depends on the noise volt-
age on the internal the reference node. The de-coupling
capacitor on the V
internal reference. This capacitor should be larger than 1nF;
having a larger capacitor value will result in a lower noise
voltage on the Mic Bias output.
Most of the logic levels for the digital control interface are rel-
ative to I
controller of the application containing the LMV1089. The
supply voltage on the I
age on the V
Only the four pins that determine the default power up gain
(as described in
levels relative to V
Shutdown Function
As part of the Powerwise™ family, the LMV1089 consumes
only 1.1mA of current. In many applications the part does not
need to be continuously operational. To further reduce the
power consumption in the inactive period, the LMV1089 pro-
2
CV
2
C and four control pins. Both methods are de-
DD
DD
pin.
voltage. This eases interfacing to the micro
SETTING ADJUSTABLE
REF
DD
.
pin determines the noise voltage on this
2
CV
DD
pin must never exceed the volt-
FIGURE 4. Simplified Block Diagram of the LMV1089
DD
in less than 100ms.
GAIN) have logic
15
cation system. A simplified block diagram is provided in
Figure
vides two individual microphone power down functions. When
either one of the shutdown functions is activated the part will
go into shutdown mode consuming only a few μA of supply
current.
SHUTDOWN VIA HARDWARE PIN
The hardware shutdown function is operated via the EN pin.
In normal operation the EN pin must be at a 'high' level
(V
the part will go into shutdown mode disabling all internal cir-
cuits.
SHUTDOWN VIA I
The LMV1089 offers an additional shutdown function by re-
programming an I
only consume power in a mode where it can perform its nor-
mal 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
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
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 inde-
pendent of each other. In most applications the gain will be
set via the I
SETTING ADJUSTABLE GAIN
The LMV1089 provides four pins to set the default gain set-
tings 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
one of the four possible values in the 12dB to 36dB range (see
Table
in the same way by connecting the GB0 and GB1 pins to ei-
ther V
Table
DD
). Whenever a 'low' level (GND) is applied to the EN pin
DD
3). Setting the gain of the preamplifier and post amplifier
2) can be chosen. The default post amplifier gain is set
4.
or GND to select a gain between 6dB and 15dB (see
2
2
C interface, see
C 'A' register (address 0x01h) of the LMV1089
2
C register (see
2
C
Table
Table
6.
DD
6). The LMV1089 will
30047224
or GND. In this way,
www.national.com
2
C,