A3935 Allegro MicroSystems, Inc., A3935 Datasheet - Page 10

• Manufacturer Part Number: A3935
• Description: Three-Phase Power MOSFET Controller
• Manufacturer: Allegro MicroSystems, Inc.

Motor Lead Protection. A fault detection circuit monitors
the voltage across the drain to source of the external MOSFETs.
A fault is asserted “low” on the output terminal, FAULT, if the
drain-to-source voltage of any MOSFET that is instructed to turn
on is greater than the voltage applied to the V
When a high-side switch is turned on, the voltage from V
the appropriate motor phase output, V
motor lead is shorted to ground before the high side is turned on,
the measured voltage will exceed the threshold and the FAULT
terminal will go “low”. Similarly, when a low-side MOSFET is
turned on, the differential voltage between the motor phase
(drain) and the LSS terminal (source) is monitored. V
by a resistor divider to V
The V
side, drain-source monitor circuit. Voltage drops across the
power bus are eliminated by connecting an isolated PCB trace
from the V
This allows improved accuracy in setting the V
voltage. The low-side, drain-source monitor uses the LSS
terminal, rather than V
The A3935 merely reports these motor faults.
Fault Outputs. Transient faults on any of the fault outputs are
to be expected during switching and will not disable the gate
drive outputs. External circuitry or controller logic must
determine if the faults represent a hazardous condition.
FAULT. This terminal will go active “low” when any of the
following conditions occur:
10
3935
THREE-PHASE POWER
MOSFET CONTROLLER
DRAIN
V
V
V
Motor lead short-to-ground,
Motor lead short-to-supply (or battery),
Bridge (or V
V
Thermal shutdown.
BAT
BAT
REG
DD
DRAIN
is intended to be a Kelvin connection for the high-
undervoltage, or
overvoltage,
undervoltage,
undervoltage,
terminal to the drain of the MOSFET bridge.
DRAIN
DRAIN
DD
) open,
.
, in comparing against V
SX
, is examined. If the
DSTH
DSTH
input terminal.
Functional Description
threshold
DSTH
DSTH
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
.
DRAIN
is set
to
OVFLT. Asserts “high” when a V
and resets “low” after a recovery hysteresis. It has a high-
impedance state when a thermal shutdown or V
occurs. The voltage at the OVSET terminal, V
the V
where K
V
variables must be in range and below maximum operating
specification.
UVFLT. Asserts “high” when a V
and resets “low” after a recovery hysteresis. It has a high-
impedance state when a thermal shutdown or V
occurs. OVFLT and UVFLT are mutually exclusive by defini-
tion.
Current Sensing. A current-sense amplifier is provided to
allow system monitoring of the load current. The differential
amplifier inputs are intended to be Kelvin connected across a
low-value sense resistor or current shunt. The output voltage is
represented by:
where V
and A
Shutdown. If a fault occurs because of excessive junction
temperature or undervoltage on V
outputs are driven “low” until the fault condition is removed. In
addition, the boost supply switch and the VREG are turned “off”
until those undervoltages and junction temperatures recover.
Boost Supply. V
control loop, and by an outer voltage-feedback loop. The
current-control loop turns “off” the boost switch for 5 µs
whenever the voltage across the boost current-sense resistor
exceeds 500 mV. A diode reverse-recovery current flows
through the sense resistor whenever the boost switch turns “on”,
which could turn it “off” again if not for the “blanking time”
circuit. Adjustment of this external sense resistor determines the
maximum current in the inductor. Whenever V
predefined threshold, nominally 16 V, the boost switch is
inhibited.
BAT(ov)
BAT
V
is the differential amplifier gain of about 19.2.
when V
BAT(ov)
OS
V
V
overvoltage set point V
BAT(ov)
CSOUT
is the output voltage calibrated at zero load current
is the gain (12) and V
SET(ov)
= ( I
= (K
BOOST
LOAD
BAT(ov)
is zero (~22.4). For valid formula, all
is controlled by an inner current-
x A
x V
V
x R
SET(ov)
BAT(ov)
DD
BAT
BAT
S
) + V
BAT(ov)
or V
) + V
, i.e.,
overvoltage fault occurs
undervoltage fault occurs
OS
BAT
(0) is the value of
BAT(ov)
, all gate driver
OVSET
DD
DD
BOOST
(0),
undervoltage
undervoltage
, controls
exceeds the