L9654 datasheet(28/59 Pages) STMICROELECTRONICS

28 / 59 page

Functional description

L9654

28/59

DocID14218 Rev 3

A low pass filter (10 kΩ + 330 pF) is recommended in order to cancel the noise caused by

internal offset compensation.

Figure 15. Resistance measurement flow chart

4.10.6

MOS diagnostics

During diagnostic, IBIAS is connected to SQH pin. In a normal condition, SQH voltage is

below SBTH and SQL voltage is higher than SGTH. Prior to turning on the MOS, the

processor is expected to check for a short to battery and a short to ground fault. This step is

intended to prevent a large amount of current from flowing through the MOS. Also, this step

is intended to precondition SQH and SQL pins prior to diagnostics. DEPEN pin is asserted

in order to turn on the low or high-side driver. If DEPEN is negated during diagnostic, the

MOS is not turned on and a fail MOS diagnostic is expected.

4.10.7

Low-side MOS diagnostic

When L9654 receives an SPI command to initiate the low-side driver diagnostic, verification

of following conditions is done before turning on the low-side driver:



VSQL greater than SGTH threshold voltage



VSQH less than SBTH threshold voltage

If both conditions above are satisfied, execution of low-side driver diagnostic is performed.

Otherwise, the low-side MOS diagnostic request is ignored and both bit D13 and bit D7 in

SPI diagnostic mode response are set. Upon detection of the following conditions, the

device turns the low-side driver off and terminates the diagnostic within the specified time,

tPROP_DLY.



VSQL less than SGTH threshold voltage



(VSQHx – VSQLx) greater than VI_TH



VSQH greater than SBTH threshold voltage

The state of each comparator above is reported through SPI. When the device detects one

of the above conditions, the respective SPI status bit indicates that the condition is set. Any

of the above conditions is considered as normal in a low-side MOS diagnostic.

The low-side driver is turned off when tTIMEOUT is expired. A fault detection filter, tFLT_DLY, is

provided to protect against short-transients on SQH and SQL pins.

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