- Device state: ACTIVE - high-side
recirculation
- Mechanism and threshold: On-state diagnostics
(OLA) can detect an open load detection in the
ACTIVE state during high-side recirculation. This
includes high-side load connected directly to VM
or through a high-side FET on the other
half-bridge. During a PWM switching transition,
the inductive load current re-circulates into VM
through the HS body diode when the LS FET is
turned OFF. The device looks for a voltage spike
on OUTx above VM during the brief dead time,
before the HS FET is turned ON. To observe the
voltage spike, this load current needs to be
higher than the pull down current
(IPD_OLA) on the output asserted by the
FET driver. Device has configurable bit OLA_FLTR
(CONFIG4) for either "16" or "1024"
consecutive re-circulation switching cycles with
absence of this voltage spike to indicate a loss
of load inductance or increase in load resistance
and is detected as an OLA fault.
- Action:
- nFAULT pin is asserted low
- Output - normal function maintained
- IPROPI pin - normal function maintained
- Reaction configurable between latch setting and
retry setting. In retry setting, OLA fault is
automatically cleared with the detection of either
"16" or "1024" consecutive voltage spikes during
re-circulation switching cycles.
- OLA Fault Behavior during direction change:
-
Retry mode - If an open load condition is
detected on OUTx, OLAx bit is set if condition
persists for longer than the filter time. OLAx
filter is cleared on direction change.
-
Latch mode - If an open load condition is
detected on OUTx, OLAx is set if condition
persists for longer than the filter time. OLAx
remains latched until a CLR_FLT command is issued.
OLAx filter is cleared on direction change.
- OLA Fault Behavior during CLR_FLT command:
-
Retry mode - CLR_FLT command is not used.
-
Latch mode - If an open load condition is
detected on OUT1, OLA1 is set if condition
persists for
longer than the filter time. OLAx remains latched
until a CLR_FLT command is issued, which is
cleared regardless of open load condition. If the
condition does exist, OLA fault is reported again
after the filter time.
This monitoring is optional and can be
disabled.
Note: OLA
is not supported for low-side loads (low-side
recirculation).