Messages in this thread | | | Subject | Re: [PATCH] vf610_adc: Fix internal temperature calculation | From | Bhuvanchandra <> | Date | Tue, 29 Sep 2015 10:22:57 +0530 |
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Hi Fugang,
On 09/27/2015 09:23 PM, Jonathan Cameron wrote:
> On 23/09/15 14:43, Bhuvanchandra DV wrote: >> There is an observed temperature difference of ~20°C with the >> internal temperature reading and the temperature measured on >> SoC package. Existing calculations consider the typical values >> provided in datasheet. Those typical values are valid for >> VREFH_ADC at 3.0V. Voltage at 25°C 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 and the final temperature readings differs with ~5°C from >> the external readings. >> >> 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> > Looks fine to me, but I'll need an Ack from Fugang on this one > as I don't know or have the part I'm afraid.
Can you please give your ACK if the patch looks fine.
Best regards, Bhuvan
> > Jonathan >> --- >> 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 f4df2a7..e7abc13 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, >> @@ -636,11 +643,13 @@ 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); >>
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