L9305 datasheet(43/107 Pages) STMICROELECTRONICS

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8.3.1

Safety switch-off path electrical characteristics

4.75 V ≤ VDD ≤ 5.5 V; 5.5 V ≤ VBATP ≤ 19 V; -40 °C ≤ Tj ≤ 175 °C unless otherwise noted. All voltages refer to

GNDA pin.

Table 31. Oscillator safety switch-off path parameter

Symbol

Parameter

Test condition

Min

Typ

Max

Unit

tSAFETYn echo_deglitch

Digital deglitch of safetyn echo

Guaranteed by scan

0.2

–

µs

8.4

Valve drivers

To verify current control integrity, various diagnostic tests are integrated throughout the control path and are

explained in the following sections.

8.4.1

High side – low side current sense compare

Load current is monitored in both the high side and low side solenoid drivers. The current sensing circuits are

independent. The current sense output is multiplexed into an analog to digital converter to close the control loop.

To verify the correct current sense functionality, an automatic check between the high and low side current

measurements can be made. In the Measured H/L Delta Current register is stored the actual difference between

the current sensed from HS and LS circuits, this measured delta current value can be read at power-on by the

microcontroller and its value can be written into the Base H/L Delta Current Register, in order to compensate

known systematic offsets or delta induced by asymmetrical load transient response and to improve check

accuracy. Once the device has the Base H/L Delta Current value recorded, it will continuously monitor the high

and low side current values and should the difference exceed the Base H/L Current value, the HS/LS compare

fault bit is set (EXCEPTIONS2 register, D[1]). The microcontroller may also perform the same test by simply

reading the Measured H/L Delta Current value on a continuous basis and check for deviations.

The current step value is 2 mA per bit. The HS/LS compare fault bit, ie D[1] in the EXCEPTIONS2 register is set

high in case the measured current delta exceed the value ± (25 mA + 12.5%*Isetpoint). An example waveform is

shown below in Figure 19.

The current step value is measured and sensed. Delta values are stored in SPI registers with two’s complement

format:

MeasuredDeltaCurrent=2ComplementMeasDeltaCurrent7:0 *2mA

(3)

Figure 19. HS/LS current compare example

1.15

1.1

1.05

0.95

0.9

0.85

PWM

Current

DeltaLS→HS

DeltaHS→LS

Delta(I) = average(DeltaLS→HS, DeltaHS→LS)

GADG2709181329PS

L9305

Safety features

DS12774 - Rev 10

page 43/107

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