33926 Datasheet, PDF (15/24 Pages) Freescale Semiconductor, Inc – 5.0 A Throttle Control H-Bridge

FUNCTIONAL DEVICE OPERATION
PROTECTION AND DIAGNOSTIC FEATURES
PROTECTION AND DIAGNOSTIC FEATURES
SHORT CIRCUIT PROTECTION
If an output short circuit condition is detected, the power
outputs tri-state (latch-OFF) independent of the input (IN1
and IN2) states, and the fault status output flag (SF) is SET
to logic LOW. If the D1 input changes from logic HIGH to logic
LOW, or if the D2 input changes from logic LOW to logic
HIGH, the output bridge will become operational again and
the fault status flag will be reset (cleared) to a logic HIGH
state.
The output stage will always switch into the mode defined
by the input pins (IN1, IN2, D1, and D2), provided the device
junction temperature is within the specified operating
temperature range.
INTERNAL PWM CURRENT LIMITING
The maximum current flow under normal operating
conditions should be less than 5.0 A. The instantaneous load
currents will be limited to I_LIM via the internal PWM current
limiting circuitry. When the I_LIM threshold current value is
reached, the output stages are tri-stated for a fixed time (T _A)
of 20 µs typical. Depending on the time constant associated
with the load characteristics, the output current decreases
during the tri-state duration until the next output ON cycle
occurs.
The PWM current limit threshold value is dependent on the
device junction temperature. When - 40°C < T_J < 160°C, I_LIM is
between the specified minimum/maximum values. When T_J
exceeds 160 °C, the I_LIM threshold decreases to 4.2 A.
Shortly above 175 °C the device overtemperature circuit will
detect T_LIM and an overtemperature shutdown will occur. This
feature implements a graceful degradation of operation
before thermal shutdown occurs, thus allowing for
intermittent unexpected mechanical loads on the motor’s
gear-reduction train to be handled.
Important Die temperature excursions above 150×C are
permitted only for non-repetitive durations < 30 seconds.
Provision must be made at the system level to prevent
prolonged operation in the current-foldback region.
OVERTEMPERATURE SHUTDOWN AND
HYSTERESIS
If an overtemperature condition occurs, the power outputs
are tri-stated (latched-OFF) and the fault status flag (SF) is
SET to logic LOW.
To reset from this condition, D1 must change from logic
HIGH to logic LOW, or D2 must change from logic LOW to
logic HIGH. When reset, the output stage switches ON again,
provided that the junction temperature is now below the
overtemperature threshold limit minus the hysteresis.
Important Resetting from the fault condition will clear the
fault status flag. Powering down and powering up the device
will also reset the 33926 from the fault condition.
OUTPUT AVALANCHE PROTECTION
An inductive fly-back event, namely when the outputs are
suddenly disabled (tri-stated) and VPWR is lost, could result
in electrical overstress of the drivers. To prevent this the
VPWR input to the 33926 should not exceed 40 V during a
fly-back condition. This may be done with either a zener
clamp or MOV, and/or an appropriately valued input
capacitor with sufficiently low ESR (see Figure 12).
VPW _R
Bu lk
Low ESR
Cap.
10 0nF
VPW R
OUT1
M
9
I/Os
OUT2
AGND PGND
Figure 12. Avalanche Protection
Analog Integrated Circuit Device Data
Freescale Semiconductor
33926
15