a4935 Allegro MicroSystems, Inc., a4935 Datasheet - Page 9

• Manufacturer Part Number: a4935
• Description: Automotive 3-phase Mosfet Driver
• Manufacturer: Allegro MicroSystems, Inc.

A4935
In some applications a safety resistor is added between the gate
and source of each FET in the bridge. When a high-side FET is
held in the on-state, the current through the associated high-side
gate-source resistor (R
therefore appears as a static resistive load on the top-off charge
pump. The minimum value of R
pump can provide current is shown in the Electrical Characteris-
tics table.
GLA, GLB, and GLC Pins
outputs for the external N-channel MOSFETs. External resistors
between the gate drive output and the gate connection to the FET
(as close as possible to the FET) can be used to control the slew
rate seen at the gate, thereby providing some control of the di/dt
and dv/dt of the SA, SB, and SC outputs. GLx going high turns on
the upper half of the drive, sourcing current to the gate of the low-
side FET in the external power bridge, turning it on. GLx going
low turns on the lower half of the drive, sinking current from the
external FET gate circuit to the LSS pin, turning off the FET.
SA, SB, and SC Pins
terminals sense the voltages switched across the load. These
terminals are also connected to the negative side of the bootstrap
capacitors and are the negative supply connections for the floating
high-side drives. The discharge current from the high-side FET
gate capacitance flows through these connections, which should
have low impedance circuit connections to the FET bridge.
GHA, GHB, and GHC Pins
drive outputs for the external N-channel FETs. External resistors
between the gate drive output and the gate connection to the FET
(as close as possible to the FET) can be used to control the slew
rate seen at the gate, thereby controlling the di/dt and dv/dt of the
SA, SB, and SC outputs. GHx going high turns on the upper half of
the drive, sourcing current to the gate of the high-side FET in the
external motor-driving bridge, turning it on. GHx going low turns
on the lower half of the drive, sinking current from the external
FET gate circuit to the corresponding Sx pin, turning off the FET.
CA, CB, and CC Pins
for the bootstrap capacitors and are the positive supply for the
high-side gate drives. The bootstrap capacitors are charged to
approximately V
low. When the Sx output swings high, the charge on the bootstrap
capacitor causes the voltage at the corresponding Cx terminal to
rise with the output to provide the boosted gate voltage needed
for the high-side FETs.
REG
when the associated output Sx terminal is
Directly connected to the motor, these
GSH
These are the high-side connections
) is provided by the high-side drive and
These are the low-side gate drive
These terminals are the high-side gate
GSH
for which the top-off charge
Automotive 3-Phase MOSFET Driver
LSS Pin
capacitance on the FET gates. It should be tied directly to the
common sources of the low-side external FETs through an inde-
pendent low impedance connection.
RDEAD Pin
during FET switching.
• When a resistor greater than 3 kΩ is connected between
• When RDEAD is connected directly to VDD, cross-conduction
• When RDEAD is connected directly to AGND, internal dead
Logic Control Inputs
Low voltage-level digital inputs provide control for the gate
drives. The input logic is shown in table 1.
These logic inputs can be driven from either 3.3 or 5 V logic. All
have a nominal hysteresis of 500 mV to improve noise perfor-
mance.
AHI, BHI, CHI, ALO, BLO, and CLO Pins
control inputs. The xHI inputs control the high-side drives and
the xLO inputs control the low-side drives. Internal lockout
logic ensures that the high-side output drive and low-side output
drive cannot be active simultaneously, except when RDEAD is
connected to AGND and at the same time CCEN is set high, as
described in the CCEN pin section.
PWMH and PWML Pins
control motor torque and speed.
• Setting PWMH low turns off active high-side drives and turns
RDEAD and AGND, cross-conduction is prevented by the gate
drive circuits, which introduce a dead time, t
switching one FET off and the complementary FET on. The
dead time is derived from the resistor value connected between
the RDEAD and AGND pins.
is prevented by the gate drive circuits. In this case, t
defaults to a value of 6 μs typical.
time generation is disabled. This allows dead times of any
duration to be determined by the external controller through the
relative timing of the phase logic control inputs, xHI and xLO.
Note that when using an external controller to determine the
dead time, care must be taken to ensure that unintentional shorts
across the supply are avoided.
on the complementary low-side drives. This provides high-
side–chopped slow-decay PWM with synchronous rectification.
This is the low-side return path for discharge of the
This pin controls internal generation of dead time
These inputs can be used to externally
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
These are the phase
DEAD
, between
DEAD
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