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drivers: hwmon: max31827: add max31875
MAX31875 Low-Power I2C Temperature Sensor Signed-off-by: John Erasmus Mari Geronimo <[email protected]>
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@@ -29,9 +29,18 @@ Supported chips: | |
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Datasheet: Publicly available at the Analog Devices website | ||
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* Maxim MAX31875 | ||
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Prefix: 'max31875' | ||
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Addresses scanned: I2C 0x48 - 0x4f | ||
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Datasheet: Publicly available at the Analog Devices website | ||
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Authors: | ||
- Daniel Matyas <[email protected]> | ||
- John Erasmus Mari Geronimo <[email protected]> | ||
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Description | ||
----------- | ||
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@@ -45,13 +54,20 @@ configured to operate in the same manner with 1 write operation to the | |
configuration register. From here on, we will refer to all these chips as | ||
MAX31827. | ||
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MAX31827 implements a temperature sensor with a 6 WLP packaging scheme. This | ||
sensor measures the temperature of the chip itself. | ||
This driver also supports the MAX31875. Its fault queue is set to 1 and it has | ||
no alarm polarity. | ||
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MAX31827 implements a temperature sensor with a 6 WLP packaging scheme while | ||
MAX31875 has a 4 WLP packaging scheme. This 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 | ||
hysteresis value: -40 and -30 degrees for under temperature alarm and +100 and | ||
+90 degrees for over temperature alarm. | ||
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MAX31875 has only an over temperature alarm with an effective value and a | ||
hysteresis value: +80 and +75 degrees. | ||
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The alarm can be configured in comparator and interrupt mode from the | ||
devicetree. In Comparator mode, the OT/UT status bits have a value of 1 when the | ||
temperature rises above the TH value or falls below TL, which is also subject 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 | ||
a set frequency. When powered on, the chip measures temperatures with 1 conv/s. | ||
a set frequency. When powered on, the MAX31827 measures temperatures with 1 | ||
conv/s while the MAX31875 measures temperatures with 0.25 conv/s or 1 conv/4s. | ||
The conversion rate can be modified with update_interval attribute of the chip. | ||
Conversion/second = 1/update_interval. Thus, the available options according to | ||
the data sheet are: | ||
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- 64000 (ms) = 1 conv/64 sec | ||
- 32000 (ms) = 1 conv/32 sec | ||
- 16000 (ms) = 1 conv/16 sec | ||
- 4000 (ms) = 1 conv/4 sec | ||
- 1000 (ms) = 1 conv/sec (default) | ||
- 4000 (ms) = 1 conv/4 sec (MAX31875 default) | ||
- 1000 (ms) = 1 conv/sec (MAX31827 default) | ||
- 250 (ms) = 4 conv/sec | ||
- 125 (ms) = 8 conv/sec | ||
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The MAX31875 only supports the last four values above. | ||
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Enabling the device when it is already enabled has the side effect of setting | ||
the conversion frequency to 1 conv/s. The conversion time varies depending on | ||
the resolution. | ||
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@@ -97,16 +116,16 @@ available resolutions are: | |
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- 8 bit -> 8.75 ms conversion time | ||
- 9 bit -> 17.5 ms conversion time | ||
- 10 bit -> 35 ms conversion time | ||
- 12 bit (default) -> 140 ms conversion time | ||
- 10 bit (MAX31875 default) -> 35 ms conversion time | ||
- 12 bit (MAX31827 default) -> 140 ms conversion time | ||
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There is a temp1_resolution attribute which indicates the unit change in the | ||
input temperature in milli-degrees C. | ||
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- 1000 mC -> 8 bit | ||
- 500 mC -> 9 bit | ||
- 250 mC -> 10 bit | ||
- 62 mC -> 12 bit (default) - actually this is 62.5, but the fil returns 62 | ||
- 250 mC -> 10 bit (MAX31875 default) | ||
- 62 mC -> 12 bit (MAX31827 default) - actually this is 62.5, but the fil returns 62 | ||
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When chip is in shutdown mode and a read operation is requested, one-shot is | ||
triggered, the device waits for <conversion time> ms, and only after that is | ||
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@@ -125,7 +144,8 @@ Bus timeout resets the I2C-compatible interface when SCL is low for more than | |
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Alarm polarity determines if the active state of the alarm is low or high. The | ||
behavior for both settings is dependent on the Fault Queue setting. The ALARM | ||
pin is an open-drain output and requires a pullup resistor to operate. | ||
pin is an open-drain output and requires a pullup resistor to operate. The | ||
MAX31875 does not have this feature. | ||
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The Fault Queue bits select how many consecutive temperature faults must occur | ||
before overtemperature or undertemperature faults are indicated in the | ||
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