A4931MET-T Allegro Microsystems Inc, A4931MET-T Datasheet - Page 7

• Manufacturer Part Number: A4931MET-T
• Description: IC DC MOTOR PREDRIVER 3PH 28QFN
• Manufacturer: Allegro Microsystems Inc

Specifications of A4931MET-T

• Applications: DC Motor Driver, Brushless (BLDC), 3 Phase
• Number Of Outputs: 1
• Voltage - Supply: 8 V ~ 33 V
• Operating Temperature: -20°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 28-VFQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Voltage - Load: -

A4931
Current Regulation
fixed off-time PWM control circuit. When the outputs of the full
bridge are turned on, current increases in the motor winding until
it reaches a value, I
When I
enable latch, turning off the source driver. At this point, load
inductance causes the current to recirculate for the fixed off-time
period.
Enable Logic
external PWM. ENB low turns on the selected sink-source pair.
ENB high switches off the appropriate drivers and the load
current decays. If ENB is held low, the current will rise until it
reaches the level set by the internal current control circuit. Typi-
cally PWM frequency is in 20 kHz to 30 kHz range. If the ENB
high pulse width exceeds 3 ms, the gate outputs are disabled. The
Enable logic is summarized in the following table:
Fixed Off-Time
nominal.
PWM Blank Timer
spike occurs due to the reverse recovery currents of the clamp
diodes as well as switching transients related to distributed
capacitance in the load. To prevent this current spike from errone-
ously resetting the source Enable latch, the sense comparator is
blanked. The blanking timer runs after the off-time counter com-
1 for > 3 ms typical
ENB Pin Setting
TRIP
0
1
is reached, the sense comparator resets the source
The Enable input terminal (ENB pin) allows
TRIP
I
The A4931 fixed off-time is set to 25 μs
TRIP
, given by:
When a source driver turns on, a current
Source Chopped
= 200 mV / R
Load current is regulated by an internal
Outputs
On
Off
SENSE .
Slow Decay with
Outputs State
Synchronous
Rectification
Disable
Drive
Functional Description
3-Phase Brushless DC Motor Pre-Driver
pletes, in order to provide the blanking function. The blanking
timer is reset when ENB is chopped or DIR is changed. With
external PWM control, a DIR change or an ENB on triggers the
blanking function. The duration is fixed at 1.5 μs.
Synchronous Rectification
triggered, either by a chop command on ENB or by an internal
fixed off-time cycle, load current recirculates. The A4931 syn-
chronous rectification feature turns on the appropriate MOSFETs
during the current decay, and effectively shorts out the body
diodes with the low R
significantly and can eliminate the need for external Schottky
diodes.
Brake Mode
mode. A logic high allows normal operation. Braking turns on all
three sink drivers, effectively shorting out the motor-generated
BEMF. The BRAKEZ input overrides the ENB input and also the
Lock Detect function.
It is important to note that the internal PWM current control cir-
cuit does not limit the current when braking, because the current
does not flow through the sense resistor. The maximum current
can be approximated by V
insure that the maximum ratings of the A4391 are not exceeded
in the worse case braking situation, high speed and high inertial
load.
HBIAS Function
7.5 V, current-limited to 30 mA. This reference voltage is used to
power the logic sections of the IC and also to power the external
Hall elements.
Standby Mode
to the current draw of the external Hall elements, Standby mode
turns off the HBIAS output voltage. Standby mode is triggered
A logic low on the BRAKEZ pin activates Brake
To prevent excessive power dissipation due
This function provides a power supply of
DS(on)
BEMF
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
driver. This lowers power dissipation
/ R
LOAD
When a PWM-off cycle is
. Care should be taken to
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