L99UDL01 datasheet(25/88 Pages) STMICROELECTRONICS

25 / 88 page

DS12511 Rev 5

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L99UDL01

Device description

2.6

Diagnostics and protections

2.6.1

Shorted load detection

All integrated drivers are protected for shorts to ground or supply by a simple over current

detection and latch off strategy. At turn on there is a blanking time (tOC_BLANKING) where the

output is given time to turn on. After the blanking time if the output current exceeds (IOC) for

longer than the filter time the faulted output(s) will be latched off.

If a shorted condition occurs after an output is active just the filtering time applies to the

latch-off action.

The fault will be reported in the fault register (Register 10H). The Global fault Functional

Error 1 bit (FE1) will also be set.

IOC applies to a single output. Multiple outputs in parallel will multiply the IOC value

accordingly. Two outputs in parallel will garner a 2x increase in the IOC value. The same

concept applies in order to have three outputs in parallel.

Since this system relies on current limitation for normal running IOC can occur in one of two

ways. First, the IOC threshold can occur if the current rise time is longer than the minimum

on time (tOC_BLANKING) of the driver. This occurs as a shorted load has very little inductance.

The second method is when the integrated driver is programmed as a simple switch and

does not provide the current regulation. Then IOC is the only means of overcurrent

protection.

The external half bridges are used as a simple switch (not current regulated). However,

when both sides of the H-Bridge are set up by the use of integrated half bridges



(outputs 1-6) then one of the integrated half bridges should be programmed as a simple

switch. This is done by programming the output to be Voltage controlled (by setting the

PWM_SW_x bit to 1) and setting the duty cycle to 100%.

This allows the other half bridge to provide the lock motor current regulation without

confusion.

Shorted outputs may be detected in the off-state as well (see Section 2.6.3).

Limitations due to active freewheeling

Due to how active freewheeling is performed (see Active freewheeling) a short to the drive

rail (a short to B+ for high side drive / low side freewheeling and vice versa) prior to

activation is not detected. The freewheeling element is never active and cannot experience

a shorted condition.

As a result, a shorted drive element during current regulation (C/PWM_SW_x=0) may

appear as a CNR (current not reached). A shorted drive element cannot be detected if PWM

control (C/PWM_SW_x=1) is selected.

A shorted driving element can be detected by reading the current feedback for that output or

by an off state fault detection. Only if the short occurs while freewheeling, can a short be

detected on the freewheeling element of the output.

External MOSFET protection

In case of the external half bridges Drain-Source voltage detection is implemented as an

overload protection once the driver is active. The Drain-Source threshold, VDS_TH, and

duration, tVDS_BLANK, are both programmable with a wide range to select from.

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