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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>
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1 changed files with 14 additions and 5 deletions
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@ -103,6 +103,13 @@
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#define DEFAULT_SAMPLE_TIME 1000
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/* V at 25°C of 696 mV */
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#define VF610_VTEMP25_3V0 950
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/* V at 25°C of 699 mV */
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#define VF610_VTEMP25_3V3 867
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/* Typical sensor slope coefficient at all temperatures */
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#define VF610_TEMP_SLOPE_COEFF 1840
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enum clk_sel {
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VF610_ADCIOC_BUSCLK_SET,
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VF610_ADCIOC_ALTCLK_SET,
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@ -635,11 +642,13 @@ static int vf610_read_raw(struct iio_dev *indio_dev,
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break;
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case IIO_TEMP:
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/*
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* Calculate in degree Celsius times 1000
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* Using sensor slope of 1.84 mV/°C and
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* V at 25°C of 696 mV
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*/
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*val = 25000 - ((int)info->value - 864) * 1000000 / 1840;
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* Calculate in degree Celsius times 1000
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* Using the typical sensor slope of 1.84 mV/°C
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* and VREFH_ADC at 3.3V, V at 25°C of 699 mV
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*/
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*val = 25000 - ((int)info->value - VF610_VTEMP25_3V3) *
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1000000 / VF610_TEMP_SLOPE_COEFF;
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break;
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default:
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mutex_unlock(&indio_dev->mlock);
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