L9788 datasheet(86/264 Pages) STMICROELECTRONICS

86 / 264 page

Low-side drivers

L9788

86/264

DS12308 Rev 4

The Diagnostic in Off state is done by the following blocks:



An internal Buffer using the pull up/down currents is able to force the VOUTOPEN

voltage on the Low-Side Driver Output when the driver is in Open Load Condition.



A comparator to detect the Open load Condition. The Open Load fault is detected when

the Low-Side output pin is VLVT ≤ VOUT ≤ V_OL Threshold for a time longer than Diag

Filter Time.



A comparator to detect the Short to GND Condition. The Short to GND fault is detected

when the Low-Side output pin is VOUT <= VLVT Threshold for a time longer than Diag

Filter Time.

There is a bit IPUPD_MODE in CONFIG_REG2 which is controlled by a MSC bit, it is used

by external µController if it is needed to switch on/off the bigger diagnosis

current(I_LS_PU1) in fast mode.

The Fast pull up current is used to avoid the false short to tGND diagnosis when the driver

switches off in Open load condition. This current switches on after the falling edge of MSC

command (driver in off state) and remains on until the Diag Filter Time is expired or until the

VOUT is > VLVT Threshold.(note: if fast pull up current is selected, the filter time

Tflt_diagoff1 is suggested. Otherwise, the filter time Tflt_diagoff2 is suggested)

Figure 32. Low-side driver OFF state fast pull up current behavior

Despite the fast mode of all drivers in off diagnostic condition (Ipupd_MODE bit), for Injector

and Solenoid drivers there is a dedicated MSC bit (IDIAG_HIGH_SOL/IDIAG_HIGH_INJ in

CONFIG_REG13) for each kind of driver to select off diagnostic high or low pull up/down

current

By default diagnostic pull up/down currents are disabled and comparator outputs are

masked by internal logic, to enable OFF state diagnostic the channel must be put first in

tristate condition and then (if not already done with previous MSC frames) diagnostic must

be enabled.

A Filter Time (Diag Filter Time) is implemented in order to avoid detecting false diagnosis as

shown in Figure 33.

GADG0112161208PS

I_diag

Voutx

VLVT

Voutx

I_LS_PU1 + I_LS_PU2

I_LS_PU2

I_LS_PU1 + I_LS_PU2

I_diag

Tflt_diagoff1

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