A4936MET-T ALLEGRO [Allegro MicroSystems], A4936MET-T Datasheet - Page 8

• Manufacturer Part Number: A4936MET-T
• Description: 3-Phase Brushless DC Motor Pre-Driver
• Manufacturer: ALLEGRO [Allegro MicroSystems]

A4936
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 V
synchronous rectification feature is disabled.
Overtemperature Protection If die temperature exceeds
approximately 165°C, the Thermal Shutdown function will dis-
able the outputs until the internal temperature falls below the
threshold, by the hysteresis.
Lock Detect Function The A4936 monitors the Hall inputs
and the control inputs to determine if a locked rotor condition is
present. A locked rotor is determined to be present under either of
these two different conditions:
• The Hall inputs are not consistently changing.
• The proper commutation sequence is not being followed. The
If there are no Hall input changes within the lock time, t
the Hall inputs toggle between two adjacent states for longer then
t
The fault remains latched until cleared by any one of the follow-
ing actions:
• Rising or falling edge on the DIR pin.
• VBB UVLO threshold exceeded (during power-up cycle).
• PWM pin held low for > t
The lock time, t
lock
motor can be locked in a condition in which it toggles between
two specific Hall device states.
, then the outputs are disabled, and the fault is latched.
lock
, is set by a capacitor connected to the CLD
lock
/ 2.
BBOV
3-Phase Brushless DC Motor Pre-Driver
lock
, the
, or
pin. CLD produces a triangle waveform (1.67 V peak-to-peak)
with frequency linearly related to the capacitor value. t
defined as 127 cycles of this triangle waveform, or:
where:
The Lock Detect function is disabled by connecting CLD to
GND.
When BRAKE is high, lock detection is disabled. It also is dis-
abled if the PWM input remains low for the duration of the Hall
input lock detection.
FG Amplifier and Comparator A differential amplifier and
a comparator are integrated into the A4936 to amplify and shape
the FG signal from the FG coil underneath the motor. This coil
is typically created with a copper PCB trace, and as the motor
spins, the coil creates a low amplitude sinusoidal voltage with a
frequency proportional to the motor speed.
The FG input differential amplifier is biased at 2.5 V, and the gain
is set by the impedance between the FGFB pin and the FG– input.
This amplified signal is then compared to 2.5 V to create the
FGS output signal. The recommended value for the gain setting
feedback resistor is 50 to 500 kΩ. The recommended value for
the capacitor between FB+ and GND is 10 nF to 10 μF.
t
CLD is the value of the capacitor in μF.
lock
is the lock time in μs, and
t
lock
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
= CLD × 20
lock
is
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