L9374LF datasheet(36/80 Pages) STMICROELECTRONICS

36 / 80 page

Circuit description

L9374LF

36/80

DocID025414 Rev 1

4.5.2

Analog signal measure blocks

All internal analog measurements are converted into digital values for use internal to the

L9374LF. These values are accessible via SPI. The supply of the load, an equivalent

measured resistor, as well as an equivalent recirculation diode forward voltage are

measured with the same analog to digital converter sequentially.



VD, Register 5, bits D0-D8



RS, Register 11, bits D0-D8



V_FWD, Register 10, bits D0-D8

The V

D is measured by the L9374LF as the voltage present at pin D13.The value for VD

can be read in the SPI register 5 (refer to 3.3.12: VD measurement and 5.2.3: VD (address

5)).

An equivalent sense resistor is measured internal to the L9374LF. The digital value is stored

in SPI-register 11. The value is corresponding to the measurement resistor which is used for

the current controller. The digital value is multiplied with the factor of 1.8 (refer to 3.3.13: Rs

measurement and 5.2.7: Sense resistor measurement (Rs) (address 11).

This means:

Rs(SPI) = 1.8 · Rsmeasured

To get the right value of Rs it is necessary to divide the SPI-value by 1.8.

The resolution of the LSB is 8.7m

 (typ.) and the parameter range is:

V_FWD

An internal reference diode forward voltage is measured using a fixed bias current. This

corresponds to the forward voltage drop across one of the current controller freewheeling

diodes. The digital value is stored in SPI Status register 10 (refer to 3.3.14: V_FWD

measurement and 5.2.6: Reference diode voltage measurement (V_FWD) (address 10)).

Load current measurements

The load current is measured in both the on and the off state of the output. This measured

current is subtracted from the target current which is set by a digital to analog converter. The

load current difference is converted into a digital signal for each output. This digital signal is

called error average. The error average is an internal value of the current controller. The

error average is the integral of the difference between the target current and real current

within a PWM period (250 μs).

Condition

Rs-value (Ω) (after division by 1.8)

Min

0.62

Typ

1.00 (TK = 1.57 mV/K)

Max

1.58

ERRORAVG_Qx

---

Itet

arg

Ireal

–

 t



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