Commit b2864829 authored by Bhuvanchandra DV's avatar Bhuvanchandra DV Committed by Kamal Mostafa

vf610_adc: Fix internal temperature calculation

commit 6219f432 upstream.

Calculate ADCR_VTEMP25 using VTEMP25 at VREFH_ADC 3V3. Existing
calculations consider the typical values provided in datasheet.
Those typical values are valid for VREFH_ADC at 3.0V. VTEMP25
is different for different VREFH_ADC voltages. With VREFH_ADC
at 3.3V, voltage at 25°C is 0.699V. Hence update the VTEMP25
to 0.699V which gives ADCR@Temp25 as 867.

Formula for finding ADCR@Temp25:
ADCR@Temp25 = (ADCR@Vdd * V@TEMP25 * 10) / VDDconv

ADCR@Vdd for 12-Bit ADC = 4095
VDDconv = VREFH_ADC * 10

VREFH_ADC@3.3V
ADCR@Temp25 = (4095 * .699 * 10) / 33
ADCR@Temp25 ~= 867

| VREFH_ADC | V@TEMP25 | VDDconv | ADCR@Temp25 |
|   3.0V    | 0.696mV  |    30   |     950     |
|   3.3V    | 0.699mV  |    33   |     867     |
Signed-off-by: default avatarBhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Acked-by: default avatarFugang Duan <B38611@freescale.com>
Signed-off-by: default avatarJonathan Cameron <jic23@kernel.org>
Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
parent 873c6cce
...@@ -98,6 +98,13 @@ ...@@ -98,6 +98,13 @@
#define VF610_ADC_CALF 0x2 #define VF610_ADC_CALF 0x2
#define VF610_ADC_TIMEOUT msecs_to_jiffies(100) #define VF610_ADC_TIMEOUT msecs_to_jiffies(100)
/* V at 25°C of 696 mV */
#define VF610_VTEMP25_3V0 950
/* V at 25°C of 699 mV */
#define VF610_VTEMP25_3V3 867
/* Typical sensor slope coefficient at all temperatures */
#define VF610_TEMP_SLOPE_COEFF 1840
enum clk_sel { enum clk_sel {
VF610_ADCIOC_BUSCLK_SET, VF610_ADCIOC_BUSCLK_SET,
VF610_ADCIOC_ALTCLK_SET, VF610_ADCIOC_ALTCLK_SET,
...@@ -514,10 +521,12 @@ static int vf610_read_raw(struct iio_dev *indio_dev, ...@@ -514,10 +521,12 @@ static int vf610_read_raw(struct iio_dev *indio_dev,
case IIO_TEMP: case IIO_TEMP:
/* /*
* Calculate in degree Celsius times 1000 * Calculate in degree Celsius times 1000
* Using sensor slope of 1.84 mV/°C and * Using the typical sensor slope of 1.84 mV/°C
* V at 25°C of 696 mV * and VREFH_ADC at 3.3V, V at 25°C of 699 mV
*/ */
*val = 25000 - ((int)info->value - 864) * 1000000 / 1840; *val = 25000 - ((int)info->value - VF610_VTEMP25_3V3) *
1000000 / VF610_TEMP_SLOPE_COEFF;
break; break;
default: default:
mutex_unlock(&indio_dev->mlock); mutex_unlock(&indio_dev->mlock);
......
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