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Document number: BST-BME690-DS001-04

as well as in the event of applications for industrial property rights

Table 16: Variable names and register addresses for res_heat_x calculation

Variable name

par_g1

0xED

par_g2

0xEB/0xEC

par_g3

0xEE

res_heat_range

0x02 <5:4>

res_heat_val

0x00

For each of the 10 temperature steps, the heating duration must be specified. Referring to Figure 2, the heating phase starts

after the temperature, pressure and humidity measurements are complete. This means there is no heating in parallel to these

measurements, which is desirable to minimize undesired cross-influences between the various sensor components.

The heating duration is specified by writing to the corresponding gas_wait_x<7:0> control register. Heating durations

between 1 ms and 4032 ms can be configured. In practice, approximately 20–30 ms are necessary for the heater to reach

the intended target temperature.

3.7 Data readout

The procedure goes as follows, the new_data bit (see Section 5.3.6.1) can be checked to see if a new data is generated. If

gas measurements are performed the gas_valid_r (see Section 5.3.6.5) and heat_stab_r (see Section 5.3.6.6) status bits of

the respectively field should be checked to ensure that the gas measurement was successful. If heat_stab_r is zero, it

indicates that either the heating time was not enough to allow the sensor to reach to configured target temperature or that

the target temperature was too high for the sensor to reach.

After the uncompensated values of temperature, pressure and humidity have been read, the actual humidity, pressure and

temperature need to be calculated using the compensation parameters stored in the device.

Gas resistance readout

Readout of gas resistance ADC value and calculation of gas resistance consists of 2 steps

1. Read gas ADC value (gas_adc) and gas ADC range (gas_range) (see Section 5.3.5)

2. Convert ADC value into gas resistance in ohm

Using the variables listed in Table 17, the conversion is done as follows:

Floating point:

uint32_t var1 = UINT32_C(262144) >> gas_range;

int32_t var2 = (int32_t) gas_adc - INT32_C(512);

var2 *= INT32_C(3);

var2 = INT32_C(4096) + var2;

gas_res = 1000000.0f * (float)var1 / (float)var2;

Integer:

uint32_t var1 = UINT32_C(262144) >> gas_range;

int32_t var2 = (int32_t) gas_adc - INT32_C(512);

var2 *= INT32_C(3);

var2 = INT32_C(4096) + var2;

/* multiplying 10000 then dividing then multiplying by 100 instead of multiplying by 1000000 to prevent overflow */

calc_gas_res = (UINT32_C(10000) * var1) / (uint32_t)var2;

gas_res = calc_gas_res * 100;

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