MC34932 Datasheet, PDF(15/24 Page) Freescale Semiconductor, Inc

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MC34932 Datasheet, PDF (15/24 Pages) Freescale Semiconductor, Inc – Dual 5.0 A H-Bridge

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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 becomes operational again and the

fault status flag resets (cleared) to a logic HIGH state.

The output stage always switches 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 is 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 (T A) of 20 Âµs

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 Â°C < TJ < 160 Â°C, ILIM

is between the specified minimum/maximum values. When

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

Shortly above 175 Â°C the device overtemperature circuit

detects tLIM and an overtemperature shutdown occurs. This

feature implements a graceful degradation of operation

before thermal shutdown occurs, thus allowing for

intermittent unexpected mechanical loads on the motorâs

gear-reduction train to be handled.

Important Die temperature excursions above 150 Â°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 EN/D2 must change from logic LOW

to logic HIGH. When reset, the output stage switches ON

again, provided the temperature is below the

overtemperature threshold limit, EN/D2 will clear the fault.

When the junction temperature is below the overtemperature

threshold limit minus the hysteresis, D1 will clear the fault.

Important Resetting from the fault condition clears the fault

status flag. Powering down and powering up the device also

resets the 34932 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 34932 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).

VPW R

Bu lk

Low ESR

Cap.

10 0nF

VPW R

OUT1

I/Os

OUT2

AGND PGND

Figure 13. Avalanche Protection

Analog Integrated Circuit Device Data

Freescale Semiconductor

34932

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