33887 datasheet(24/37 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33887

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 is SET 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.

ACTIVE CURRENT LIMITING

The maximum current flow under normal operating

conditions is internally limited to ILIM (5.2 A to 7.8 A). When

the maximum 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

current decreases during the tri-state duration until the next

output ON cycle occurs (see Figures 11 and 14, page 13 and

page 15, respectively).

The current limiting threshold value is dependent upon the

device junction temperature. When -40

°C ≤ T

J ≤ 160°C, ILIM

is between 5.2 A to 7.8 A. When TJ exceeds 160°C, the ILIM

current decreases linearly down to 4.0 A typical at 175

°C.

Above 175

°C the device overtemperature circuit detects T

LIM

and overtemperature shutdown occurs (see Figure 9,

page 12). This feature allows the device to remain

operational for a longer time but at a regressing output

performance level at junction temperatures above 160

°C.

Output Avalanche Protection

An inductive fly-back event, namely when the outputs are

suddenly disabled and V+ is lost, could result in electrical

overstress of the drivers. To prevent this the V+ input to the

33887 should not exceed the maximum rating during a fly-

back condition. This may be done with either a zener clamp

and/or an appropriately valued input capacitor with

sufficiently low ESR.

OVERTEMPERATURE SHUTDOWN AND

HYSTERESIS

If an overtemperature condition occurs, the power outputs

are tri-stated (latched-OFF) and the fault status flag 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.

Note Resetting from the fault condition will clear the fault

status flag.

33887 Datasheet(PDF) 24 Page - Freescale Semiconductor, Inc

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