A3980(2011) View Datasheet(PDF) - Allegro MicroSystems

Part Name

Description

Manufacturer

A3980
(Rev.:2011)

Automotive DMOS Microstepping Driver with Translator

Allegro MicroSystems 

A3980

Automotive DMOS Microstepping Driver

with Translator

While the fault persists, the A3980 continues this cycle at

each step command: enabling the outputs for a short period,

and then disabling the outputs. This allows the A3980 to

handle a continuous short circuit without damage. If, while

stepping rapidly, a short circuit appears and no action is

taken, the repeated short-circuit current pulses eventually

cause the temperature of the A3980 to rise and an overtem-

perature fault occurs.

Low Load Current Fault Operation. A low load current

is detected by monitoring the measured phase current in

each output while driving the motor in the Home microstep

position. At the Home microstep position, each phase current

should reach 70% of ITripMax. If either phase current does

not exceed half of this expected value (more than 35% of

ITripMax) while in the Home microstep position, then a low

load current condition is reported on the next rising edge

of the STEP input. If the measured current in both phases

exceeds 35% of ITripMax) then no fault will be generated on

the next rising edge of the STEP input.

If an open load condition appears while stepping, then it is

detected after the translator cycles through the Home state.

Although the A3980 continues to drive the DMOS outputs

during an open load condition, it does not clear the fault flags

until the next Home state occurs.

There are two conditions that can cause a low load current.

The first is an open circuit on either or both motor phase con-

nections. In this condition, current can never flow through

the phase so a low load current will always be flagged. The

second condition is where the back EMF of the motor limits

the phase current to less than the low load current trip level.

This will happen when the stepper motor is running close to

its limiting speed. To confirm an open load condition when

a low load current is flagged, the step rate should be reduced

to a level below half the maximum step rate. If the low

load current flag remains active at the lower step rate, after

completing the number of steps required to pass the home

condition, then an open circuit condition is confirmed.

To allow immediate detection of an open load condition

at power up or after coming out of sleep mode, the A3980

translator is reset to the Home microstep position and the

low load current fault flags are set. If no open load condition

exists then the fault flags will be reset on the next rising edge

of the STEP input.

Supply Monitors. External and internal supplies are

monitored to ensure that they are within the correct operat-

ing range. If the main supply exceeds the overvoltage limit,

VOVB, the fault flags are set and the A3980 enters a safety

mode in which all low-side DMOS FETs are enabled and all

high-side DMOS FETs are disabled. This allows the A3980

to survive a load dump transient condition that has up to

50 V on VBATT and a duration of up to 500 ms. If the inter-

nal regulator VREG or the logic supply VDD go below their respec-

tive undervoltage limits (VUVR or VUVD), then: the fault flags are

set, the DMOS outputs are disabled, and the internal logic is reset

to the power-on state (the translator is set to the Home state).

Diagnostic Fault Flags (FF1, FF2). Diagnostic fault

conditions are reported using the two fault flag outputs.

These are active-low outputs which are coded as shown in

table 2 to discriminate between the fault conditions. When

both fault flags are high, no fault exists.

Allegro MicroSystems, Inc.

13

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

www.allegromicro.com

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