VNF9D5F datasheet(52/108 Pages) STMICROELECTRONICS

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Diagnostic

The device is capable of providing digital diagnostic information through the SPI interface.

5.1

Digital current sense diagnostic

5.1.1

ADC characteristics

Here are the “Differential Non Linearity” and “Integral Non Linearity” typical curves for the 10-bit ADC converter.

Figure 22. ADC characteristics and error definition

1023

1022

1021

1020

1019

1018

101710181019 10201021 10221023

code out

Iout(LSBideal)

1 LSB (Ideal)

1 LSB Ideal – VDO_ADC / 1024

Offset error (EO)

Offset error (EG)

Offset error (EO)

(2)

(3)

(4)

(5)

(1)

(1) Example of an actual transfer curve

(2)The ideal transfer curve

(3) Differential non-linearity error (DNL)

(4) Integral non-linearity error (INL)

(5) Center of a step of the actual transfer curve

5.1.2

ADC operating principle

The device provides a 10-bit Successive Approximation Register (SAR) analog to digital converter. It is used to

provide a digital information about the current sense feedback proportional to the output current and the

temperature read by the internal sensor. An integrated LP (Progressive Average) Filter can be used to filter data

coming from the ADC conversion reducing the effect of random noise coming from the analog Current Sense

amplifier.

Note:

The internal ADC is able to work in both Normal and Fail Safe conditions.

The integrated ADC control logic is designed to lead to a good 10-bit approximation of current sense/temperature

feedback.

After each conversion, an updated bit “UPDTSR” is set to advise about new conversion data. This bit is reset after

the Read process of the dedicated RAM register.

The data is maintained in the register until the next conversion results are available. The ADC register is

refreshed at the end of each conversion and maintained during the conversion of the current sample. The data is

converted on the 10-bit register, the formula is equal to: Iout_conv = data (10bit)/K.

VNF9D5F

Diagnostic

DS13946 - Rev 8

page 52/108

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