L9679ETR datasheet(93/127 Pages) STMICROELECTRONICS

93 / 127 page

10-bit data is filtered inside the digital section. The number of samples that are filtered varies depending on the

chosen conversion. As SYS_CFG, the number of used samples in converting DC sensor, squib/pyroswitch or

temperature measurements defaults to 8. The number of samples for all other measurements defaults to 4. The

sample number can be configured by accessing the SYS_CFG register. After low pass filter, the residual total

error is ±4 LSB. This error figure applies to the case of an ideal reference voltage: the spread of reference voltage

causes a proportional error in the conversion output. The reference voltage of the ADC is set to 2.5 V.

The conversion time is comprised of several factors: the number of measurements loaded into the queue, the

number of samples taken for any one measurement, and the various settling times. An example of conversion

time calculation for a full ADC request queue is reported in Figure 26. ADC conversion time. The timings reported

in the figure below are nominal ones, min/max values can be obtained by considering the internal oscillator

frequency variation reported in the DC characteristics section.

Figure 26. ADC conversion time

IQ:

Intra-Queue Settling Time = 3.5 µs

Post-ADC: Final ADC Settling Time = 3.44 µs

T_SC:

Single Sample Conversion Time = 2.25 µs

# of Samples (default = 4 for voltage only measurements)

Pre-AD C: I nitial ADC Settling Time = 4.81 µs

ADC

Pre-

DIAGCTRL_ A

S * T_SC

DIAGCTRL_B

S * T_SC

DIAGCTRL_C

S * T_SC

DIAGCTRL_D

S * T_SC

ADC

Post

GADG1203181038PS

L9679E

System voltage diagnostics

DS12485 - Rev 8

page 93/127

L9679ETR Datasheet(PDF) 93 Page - STMicroelectronics