From 6219f432ec037317a77c40910da12a626c34af1c Mon Sep 17 00:00:00 2001 From: Bhuvanchandra DV Date: Mon, 19 Oct 2015 21:24:36 +0530 Subject: [PATCH] vf610_adc: Fix internal temperature calculation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Acked-by: Fugang Duan Cc: Signed-off-by: Jonathan Cameron --- drivers/iio/adc/vf610_adc.c | 19 ++++++++++++++----- 1 file 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); -- 2.34.1