A4931
3-Phase Brushless DC Motor Pre-Driver
age on the VCP pin is internally monitored, and in case of a fault
condition, the outputs of the device are disabled.
Hall State Reporting The FG1 pin is an open drain output
that changes state at each transition of an external Hall element.
The FG2 pin is an open drain output that changes state at each
HAx transition.
Fault Shutdown In the event of a fault due to excessive
junction temperature or due to low voltage on VCP or VBB,
the outputs of the device are disabled until the fault condition
is removed. At power-up the UVLO circuit disables the drivers.
These fault conditions are latched and can only be cleared by any
one of the following actions:
Lock Detect Function The IC will evaluate a locked rotor
condition under either of these two different conditions:
• The FG1 signal is not consistently changing.
• The proper commutation sequence is not being followed. The
motor can be locked in a condition in which it toggles between
two specific Hall device states.
• Rising or falling edge on the DIR pin
• VBB UVLO threshold exceeded (during power-up cycle)
• ENB pin held high for > tlock / 2
Both of these fault conditions are allowed to persist for period
of time, tlock. tlock is set by capacitor connected to CLD pin. CLD
produces a triangle waveform (1.67 V peak-to-peak) with fre-
quency linearly related to the capacitor value. tlock is defined as
127 cycles of this triangle waveform, or:
Overvoltage Protection VBB is monitored to determine if
a hazardous voltage is present due to the motor generator pump-
ing up the supply bus. When the voltage exceeds VBBOV, the
synchronous rectification feature is disabled.
tlock = CLD × 20 s/μF
After the wait time, tlock , has expired, the outputs are disabled,
and the fault is latched. The Lock Detect function can be disabled
by connecting CLD to GND.
Overtemperature Protection If die temperature exceeds
approximately 170°C, the Thermal Shutdown function will dis-
able the outputs until the internal temperature falls below the
15°C hysteresis.
When the A4931 is in Brake mode, the Lock Detect counter is
disabled.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
8
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ALLEGRO [ ALLEGRO MICROSYSTEMS ]
