diff options
| author | Bhuvanchandra DV <bhuvanchandra.dv@toradex.com> | 2015-10-19 18:54:36 +0300 |
|---|---|---|
| committer | Jonathan Cameron <jic23@kernel.org> | 2015-10-25 15:12:29 +0300 |
| commit | 6219f432ec037317a77c40910da12a626c34af1c (patch) | |
| tree | 82e046705eabcaae564989f3e7cae6381be73575 | |
| parent | b94e22805a2224061bb263a82b72e09544a5fbb3 (diff) | |
| download | linux-6219f432ec037317a77c40910da12a626c34af1c.tar.xz | |
vf610_adc: Fix internal temperature calculation
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: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Acked-by: Fugang Duan <B38611@freescale.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
| -rw-r--r-- | drivers/iio/adc/vf610_adc.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c index 6bf4c20eb231..42d7c87ea5be 100644 --- a/drivers/iio/adc/vf610_adc.c +++ b/drivers/iio/adc/vf610_adc.c @@ -103,6 +103,13 @@ #define DEFAULT_SAMPLE_TIME 1000 +/* 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 { VF610_ADCIOC_BUSCLK_SET, VF610_ADCIOC_ALTCLK_SET, @@ -635,11 +642,13 @@ static int vf610_read_raw(struct iio_dev *indio_dev, break; case IIO_TEMP: /* - * Calculate in degree Celsius times 1000 - * Using sensor slope of 1.84 mV/°C and - * V at 25°C of 696 mV - */ - *val = 25000 - ((int)info->value - 864) * 1000000 / 1840; + * Calculate in degree Celsius times 1000 + * Using the typical sensor slope of 1.84 mV/°C + * and VREFH_ADC at 3.3V, V at 25°C of 699 mV + */ + *val = 25000 - ((int)info->value - VF610_VTEMP25_3V3) * + 1000000 / VF610_TEMP_SLOPE_COEFF; + break; default: mutex_unlock(&indio_dev->mlock); |