L9800 datasheet(36/55 Pages) STMICROELECTRONICS

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Diagnosis

The SPI communication provides diagnosis information about the device and the load status. Diagnosis

information of each channel is independent from other channels. An error condition on one channel has no

influence on the diagnostic of the others.

9.1

Overload and overtemperature

When either an overload or an overtemperature occurs on one channel, the diagnosis bit DIAG_OVC_OVT.OUTn

is set accordingly. The channel latches OFF and must be reactivated setting the corresponding

DIAG_OVC_OVT_RLW.OUTn bit to “1”. The writing operation is necessary to remove the fault as a result of the

DIAG_OVC_OVT.OUTn register is clear on write.

9.2

Off diagnosis

This diagnosis is available only in active mode. The device is able to detect two kinds of fault in off, open-load and

short to ground.

This diagnosis is available after sending an SPI request. It is performed through two different phases: the first one

distinguishes between fault and no fault condition; the second one, completed only if a fault has been found, is

intended to investigate the type of the fault.

The first phase lasts for tOFF1LS. The current generator showed in the Figure 27, marked with ‘pldw’, and driven

by dw_on, is active, and the current generator ‘plup’ is off. In this phase, if the drain voltage remains above the

prefixed threshold, the comparator output is low and it means that a load is present; otherwise, if the drain

voltages decrease below threshold, the comparator output makes a transition to “1” and sets the presence of a

fault.

After the first diagnosis interval, if a fault happened the current generator indicated with ‘plup’ and driven by the

signal up_on is activated and the other one is switched off for a time tOFF2LS.

After the pull-up activation, if the drain voltage rises and overcomes the comparator threshold again, an open-load

fault is reported. On the other hand, if the voltage remains constant and equal to zero for the whole diagnosis time

a short to ground fault is detected. If DIS pin is high an off state diagnosis request is ignored and ongoing

diagnosis is reset

The diagnosis can be requested on one or more channels in parallel. Once the diagnosis has been started, a new

diagnosis should not be sent until the ongoing diagnostic cycle is finished. Once the diagnosis is completed

DIAG_OFF_EN register is automatically cleared.

Figure 27. OFF diagnosis circuit

GADG071120231033GT

up_on

dw_on

VDS(OL)

OFF diag

3V3

VBATT

Load

Out

plup

pldw

L9800

Diagnosis

DS14041 - Rev 2

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