drivers/temp_sensor: add thermistor resistance table doc

Add the resistance table we used in the lookup table calculation in the
thermistor.c file.

BRANCH=none
BUG=none
TEST=none

Change-Id: If9d2e11b5e1b40bf67698187d99849220ff97ea6
Signed-off-by: Jett Rink <jettrink@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2904831
Reviewed-by: Tomasz Michalec <tm@semihalf.com>

2 files changed, 110 insertions, 1 deletions

diff --git a/driver/temp_sensor/thermistor.c b/driver/temp_sensor/thermistor.c
index 5a704bf990..550b2447c2 100644
--- a/driver/temp_sensor/thermistor.c
+++ b/driver/temp_sensor/thermistor.c
@@ -3,7 +3,10 @@
  * found in the LICENSE file.
  */
 
-/* Common thermistor code for Chrome EC */
+/*
+ * Common thermistor code for Chrome EC. See ./thermistor.md for table of
+ * resistance of a 47kΩ B4050 thermistor
+ */
 
 #include "adc.h"
 #include "common.h"
diff --git a/driver/temp_sensor/thermistor.md b/driver/temp_sensor/thermistor.md
new file mode 100644
index 0000000000..bb9faa04ef
--- /dev/null
+++ b/driver/temp_sensor/thermistor.md
@@ -0,0 +1,106 @@
+We used the following resistance table for a 47kΩ B4050 thermistor in the
+[thermistor.c](./thermistor.c) tables.
+
+C°   | kΩ
+--- | -----
+0   | 155.7
+1   | 147.9
+2   | 140.6
+3   | 133.7
+4   | 127.2
+5   | 121.0
+6   | 115.1
+7   | 109.6
+8   | 104.3
+9   | 99.31
+10  | 94.6
+11  | 90.13
+12  | 85.89
+13  | 81.87
+14  | 78.07
+15  | 74.45
+16  | 71.02
+17  | 67.77
+18  | 64.68
+19  | 61.75
+20  | 58.97
+21  | 56.32
+22  | 53.81
+23  | 51.43
+24  | 49.16
+25  | 47.0
+26  | 44.95
+27  | 42.99
+28  | 41.13
+29  | 39.36
+30  | 37.68
+31  | 36.07
+32  | 34.54
+33  | 33.08
+34  | 31.69
+35  | 30.36
+36  | 29.1
+37  | 27.9
+38  | 26.75
+39  | 25.65
+40  | 24.61
+41  | 23.61
+42  | 22.66
+43  | 21.75
+44  | 20.88
+45  | 20.05
+46  | 19.26
+47  | 18.5
+48  | 17.78
+49  | 17.09
+50  | 16.43
+51  | 15.8
+52  | 15.2
+53  | 14.62
+54  | 14.07
+55  | 13.54
+56  | 13.03
+57  | 12.55
+58  | 12.09
+59  | 11.64
+60  | 11.21
+61  | 10.8
+62  | 10.41
+63  | 10.04
+64  | 9.676
+65  | 9.331
+66  | 8.999
+67  | 8.68
+68  | 8.374
+69  | 8.081
+70  | 7.799
+71  | 7.528
+72  | 7.268
+73  | 7.018
+74  | 6.777
+75  | 6.546
+76  | 6.324
+77  | 6.111
+78  | 5.906
+79  | 5.708
+80  | 5.518
+81  | 5.335
+82  | 5.16
+83  | 4.99
+84  | 4.827
+85  | 4.671
+86  | 4.519
+87  | 4.374
+88  | 4.233
+89  | 4.098
+90  | 3.968
+91  | 3.842
+92  | 3.721
+93  | 3.605
+94  | 3.492
+95  | 3.384
+96  | 3.279
+97  | 3.179
+98  | 3.082
+99  | 2.988
+100 | 2.898