LMP90100MHE National Semiconductor, LMP90100MHE Datasheet - Page 26

• Manufacturer Part Number: LMP90100MHE
• Description: AFE, SENSOR, 28TSSOP
• Manufacturer: National Semiconductor

Specifications of LMP90100MHE

• Brief Features: 24bit Low Power Sigma Delta ADC, Automatic Channel Sequencer
• Supply Voltage Range: 2.7V To 5.5V
• Operating Temperature Range: -40°C To +105°C
• Digital Ic Case Style: TSSOP
• No. Of Pins: 28
• Base: RoHS Compliant
• Ic Function: Multi-Channel, Low Power 24-bit Sensor AFE
• Rohs Compliant: Yes

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16.2.1 Background Calibration
Background calibration is the process of continuously deter-
mining and applying the offset and gain calibration coeffi-
cients to the output codes to minimize the LMP90100’s offset
and gain errors. Background calibration is a feature built into
the LMP90100 and is automatically done by the hardware
without interrupting the input signal.
Four differential channels, CH0-CH3, each with its own gain
and ODRs, can be calibrated to improve the accuracy.
Types of Background Calibration:
Figure 11
calibration:
1.
2.
The benefits of using type 2 calibration is a higher throughput,
lower power consumption, and slightly better noise. The exact
savings would depend on the number of channels being
scanned, and the ODR and gain of each channel.
Using Background Calibration:
There are four modes of background calibration, which can
be programmed using the BGCALCN bits. They are as fol-
lows:
1.
2.
3.
4.
Type 1: Correction - the process of continuously
determining and applying the offset and gain calibration
coefficients to the output codes to minimize the
LMP90100’s offset and gain errors.
This method keeps track of changes in the LMP90100's
gain and offset errors due to changes in the operating
condition such as voltage, temperature, or time.
Type 2: Estimation - the process of determining and
continuously applying the last known offset and gain
calibration coefficients to the output codes to minimize
the LMP90100’s offset and gain errors.
The last known offset or gain calibration coefficients can
come from two sources. The first source is the default
coefficient which is pre-determined and burnt in the
device’s non-volatile memory. The second source is from
a previous calibration run of Type 1: Correction.
BgcalMode0: Background Calibration OFF
BgcalMode1: Offset Correction / Gain Estimation
BgcalMode2: Offset Correction / Gain Correction
Follow
using this mode.
BgcalMode3: Offset Estimation / Gain Estimation
also shows that there are two types of background
Figure 12
to set other appropriate registers when
FIGURE 11. Types of Calibration
26
If operating in BgcalMode2, four channels (with the same
ODR) are being converted, and FGA_BGCAL = 0 (default),
then the ODR is reduced by:
1.
2.
3.
4.
5.
6.
7.
8.
16.2.2 System Calibration
The LMP90100 provides System Calibration Offset and Gain
coefficients that can be used to remove system offset and
system gain errors respectively. The system offset calibration
coefficient is subtracted from the result prior to the division by
the system gain coefficient. These coefficients are typically
filled up by performing system zero-scale and system full-
scale calibrations. System zero-scale and full-scale calibra-
tions can be performed by setting up the respective calibrating
0.19% of 1.6775 SPS
0.39% of 3.355 SPS
0.78% of 6.71 SPS
1.54% of 13.42 SPS
3.03% of 26.83125 SPS
5.88% of 53.6625 SPS
11.11% of 107.325 SPS
20% of 214.65 SPS
FIGURE 12. BgcalMode2 Register Settings
30139579
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