91 lines
3.6 KiB
ReStructuredText
91 lines
3.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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Kernel driver max31827
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======================
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Supported chips:
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* Maxim MAX31827
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Prefix: 'max31827'
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Addresses scanned: I2C 0x40 - 0x5f
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Datasheet: Publicly available at the Analog Devices website
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* Maxim MAX31828
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Prefix: 'max31828'
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Addresses scanned: I2C 0x40 - 0x5f
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Datasheet: Publicly available at the Analog Devices website
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* Maxim MAX31829
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Prefix: 'max31829'
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Addresses scanned: I2C 0x40 - 0x5f
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Datasheet: Publicly available at the Analog Devices website
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Authors:
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- Daniel Matyas <daniel.matyas@analog.com>
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Description
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-----------
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The chips supported by this driver are quite similar. The only difference
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between them is found in the default power-on behaviour of the chips. While the
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MAX31827's fault queue is set to 1, the other two chip's fault queue is set to
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4. Besides this, the MAX31829's alarm active state is high, while the other two
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chip's alarms are active on low. It is important to note that the chips can be
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configured to operate in the same manner with 1 write operation to the
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configuration register. From here on, we will refer to all these chips as
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MAX31827.
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MAX31827 implements a temperature sensor with a 6 WLP packaging scheme. This
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sensor measures the temperature of the chip itself.
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MAX31827 has low and over temperature alarms with an effective value and a
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hysteresis value: -40 and -30 degrees for under temperature alarm and +100 and
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+90 degrees for over temperature alarm.
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The alarm can be configured in comparator and interrupt mode. Currently only
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comparator mode is implemented. In Comparator mode, the OT/UT status bits have a
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value of 1 when the temperature rises above the TH value or falls below TL,
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which is also subject to the Fault Queue selection. OT status returns to 0 when
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the temperature drops below the TH_HYST value or when shutdown mode is entered.
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Similarly, UT status returns to 0 when the temperature rises above TL_HYST value
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or when shutdown mode is entered.
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Putting the MAX31827 into shutdown mode also resets the OT/UT status bits. Note
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that if the mode is changed while OT/UT status bits are set, an OT/UT status
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reset may be required before it begins to behave normally. To prevent this,
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it is recommended to perform a read of the configuration/status register to
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clear the status bits before changing the operating mode.
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The conversions can be manual with the one-shot functionality and automatic with
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a set frequency. When powered on, the chip measures temperatures with 1 conv/s.
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Enabling the device when it is already enabled has the side effect of setting
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the conversion frequency to 1 conv/s. The conversion time varies depending on
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the resolution. The conversion time doubles with every bit of increased
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resolution. For 10 bit resolution 35ms are needed, while for 12 bit resolution
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(default) 140ms. When chip is in shutdown mode and a read operation is
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requested, one-shot is triggered, the device waits for 140 (conversion time) + 1
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(error) ms, and only after that is the temperature value register read.
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The LSB of the temperature values is 0.0625 degrees Celsius, but the values of
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the temperatures are displayed in milli-degrees. This means, that some data is
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lost. The step between 2 consecutive values is 62 or 63. This effect can be seen
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in the writing of alarm values too. For positive numbers the user-input value
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will always be rounded down to the nearest possible value, for negative numbers
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the user-input will always be rounded up to the nearest possible value.
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Notes
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-----
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Currently fault queue, alarm polarity and resolution cannot be modified.
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PEC is not implemented either.
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