Datasheet

PE
CAL
Calibration
Start
Calibration
Ready
Calibrating in
progress
LMV1089
SNAS441H –SEPTEMBER 2008–REVISED MAY 2010 www.ti.com
The compensation or calibration technology is achieved via memory stored coefficients when the FFNS circuitry
activates the calibration sequence. The purpose of the calibration sequence is to choose the optimized
coefficients for the FFNS circuitry for the given microphones, spacing, and acoustical design of the product
containing the LMV1089.
A basic calibration can be performed with a single 1kHz tone, however to take full advantage of this calibration
feature a three tone calibration (See PERFORMING A THREE TONE CALIBRATION) is preferred .
The automatic calibration process can be initiated from either a digital interface CALIBRATE pin (CAL) or via the
I
2
C interface.
The logic level at the PROGRAM ENABLE (PE) pin determines if the result of the calibration is volatile or
permanent. To make the result of the calibration permanent (stored in the EEPROM) the PROGRAM ENABLE
(PE) pin must be high during the automatic calibration process.
AUTOMATIC CALIBRATION VIA CAL PIN
To initiate the automatic calibration via the CAL pin, the following procedure is required. See timing diagram
Figure 30:
• From the initial condition where both PE and CAL are at 'low' level
• bring PE to a 'high' level (enable EEprom write)
• bring CAL to a 'high' level to start Calibration
• Apply Audio stimulus (single tone 1kHz or three tone sequence as described in PERFORMING A THREE
TONE CALIBRATION) (see Figure 31).
• Hold CAL 'high' for at least 790ms
• Remove Audio stimulus
• bring CAL to a 'low' level to stop Calibration
• bring PE to a 'low' level (disable EEprom write)
A tone may be applied prior to the rising of CAL and PE. Signals applied to the microphone inputs before rising
of CAL and PE are ignored by the calibration system.
Figure 29. Automatic Calibration via CAL pin
NOTE
When the I
2
C is operated, make sure that register 'R' (address 0x12) bit 0 is '0'
before operating the CAL pin (default value for this bit). When this bit is set '1' the
calibration engine of the LMV1089 is started and will remain active with a higher
supply current than normal operation. The state of the calibration remains active
until this bit is reset, '0”. With the bit set the 'low' to' high' transfer of the CAL pin
will be ignored.
AUTOMATIC CALIBRATION VIA I
2
C COMMAND
To initiate the automatic calibration via the I
2
C interface, the following procedure is required:
• From the initial condition where PE is 'low' level
• Bring PE to a 'high' level (enable EEprom write)
• Write '1' into I
2
C register 'R' (address 0x12) bit 0 to start calibration
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