33931 datasheet(16/21 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33931

FUNCTIONAL DEVICE OPERATION

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 EN/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 EN/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 ILIM via the internal PWM current

limiting circuitry. When the ILIM threshold current value is

reached, the output stages are tri-stated for a fixed time (TA)

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 <TJ <160°C, ILIM is

between the specified minimum/maximum values. When TJ

exceeds 160°C, the ILIM threshold decreases to 4.2 A. Shortly

above 175°C the device over-temperature circuit will detect

TLIM and an over-temperature 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.

OVER-TEMPERATURE SHUTDOWN AND

HYSTERESIS

If an over-temperature 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 EN/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 over-temperature 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 33931 from the fault condition.

OUTPUT AVALANCHE PROTECTION

If VPWR were to become an open circuit, the outputs

would likely tri-state simultaneously due to the disable logic.

This could result in an unclamped inductive discharge. The

VPWR input to the 33931 should not exceed 40 V during this

transient condition, to prevent electrical overstress of the

output drivers.This can be accomplished with a zener clamp

or MOV, and/or an appropriately valued input capacitor with

sufficiently low ESR (see Figure 13).

Figure 13. Avalanche Protection

OUT1

OUT2

I/Os

AGND

PGND

Bulk

Low ESR

Cap.

VPW R

100nF

VPWR

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