LMP90100MHESLASHNOPB datasheet(31/69 Pages) TI1

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1/ODR

SDO

LSB

D6 = drdyb

Valid

ADC_DOUT

(ADC Data 1)

MSB

LSB

Valid

ADC_DOUT

(ADC Data 2)

MSB

ADC

Data

ADC

Data

LMP90100

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SNAS510P – JANUARY 2011 – REVISED MARCH 2013

4. Enter the System Calibration Gain Coefficient Determination mode by programming 0x3 in the SCALCN

5. LMP90xxx starts a fresh conversion at the selected output data rate for the channel. At the end of the

conversion, the CHx_SCAL_GAIN is filled-in (or overwritten) with the System Calibration Gain coefficient.

6. The System Calibration Gain Coefficient Determination mode is automatically exited.

7. The computed calibration coefficient is accurate only to the effective resolution of the device and will

probably contain some noise. The noise factor can be minimized by computing over many times, averaging

(externally) and putting the resultant value back into the register. Alternatively, select the output data rate to

be 26.83 sps or 1.67 sps.

Post-calibration Scaling

LMP90xxx allows scaling (multiplication and shifting) for the System Calibrated result. This eases downstream

processing,

any.

Multiplication

done

using

the

System

Calibration

Scaling

Coefficient

the

CHx_SCAL_SCALING register and shifting is done using the System Calibration Bits Selector in the

CHx_SCAL_BITS_SELECTOR register.

The System Calibration Bits Selector value should ideally be the logarithm (to the base 2) of the System

Calibration Scaling Coefficient value.

There are four distinct sets of System Calibration Scaling and System Calibration Bits Selector Registers for use

with Channels 0-3. Channels 4-6 reuse the registers of Channels 0-2, respectively.

A data-flow diagram of these coefficients can be seen in Figure 47

Figure 47. Post-calibration Scaling Data-Flow Diagram

CHANNELS SCAN MODE

There are four scan modes. These scan modes are selected using the CH_SCAN: CH_SCAN_SEL bit. The first

scanned channel is FIRST_CH, and the last scanned channel is LAST_CH; they are both located in the

CH_SCAN register.

The CH_SCAN register is double buffered. That is, user inputs are stored in a slave buffer until the start of the

next conversion during which time they are transferred to the master buffer. Once the slave buffer is written,

subsequent updates are disregarded until a transfer to the master buffer happens. Hence, it may be appropriate

to check the CH_SCAN_NRDY bit before programming the CH_SCAN register.

ScanMode0: Single-Channel Continuous Conversion

LMP90xxx continuously converts the selected FIRST_CH.

Do not operate in this scan mode if gain

≥ 16 and the LMP90xxx is running in background calibration modes

BgcalMode1 or BgcalMode2. If this is the case, then it is more suitable to operate the device in ScanMode2

instead.

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