L9374LF datasheet(37/80 Pages) STMICROELECTRONICS

37 / 80 page

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L9374LF

Circuit description

The error average is a twos complement number. The range value is {-[value] … +([value]-

LSB)} and

This value is available in the SPI Status registers 13 and 14 (refer to 5.2.9: Error average

(address 13 + 14)).

Figure 22. Integration of the error average

The current controller calculates the correction factor ISAT out of the error average within an

output period (1/f_A). During a period (n) it calculates the control variable y(n) with the

current deviation e(n). At the next period n+1 the control variable y(n) is used. The value

ISAT is always stable if the load resistor value is stable. More details about the usage of

ISAT you will find in the following chapters.

4.5.3

Duty cycle calculation in the ALU

The ALU is shared between outputs 3 and 4 in the L9374LF. The following equation is used

by the ALU to provide the output PWM duty cycle information to the Duty cycle Generator.

Where:

VDR: Forward voltage of the recirculation diode (measured value stored in register V_FWD_Qx)

ITARGET: Value programmed by the SPI and provided by the Set Point Unit

RS: Sense resistor value (measured value stored in register RS)

RLSPI: Value given by the SPI

VBAT: Supply voltage of the load (measured on pin D1/3 stored in register VD)

RDS(on): fixed value of 500mOhm temperature coefficient is not respected

ISAT: Current Controller correction factor

LSB erroraverage



3.6mA

VDR ITARGET Rs



VDR VBAT ITARGET Rs RDS on



–





-------------------------------------------------------------------------------------------------------------

ITARGET RLSPI



VDR VBAT ITARGET Rs RDS on



–





-------------------------------------------------------------------------------------------------------------

ISAT 1







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