A3941 Allegro MicroSystems, Inc., A3941 Datasheet - Page 11

• Manufacturer Part Number: A3941
• Description: Automotive Full Bridge MOSFET Driver
• Manufacturer: Allegro MicroSystems, Inc.

A3941
the event that two or more faults are detected simultaneously, the
state of the fault flags will be determined by a logical OR of the
flag states for all detected faults.
Table 3. Fault Definitions
Fault States
Overtemperature
temperature threshold, typically 165°C, the A3941 will enter the
overtemperature fault state and FF1 will go high. The overtem-
perature fault state, and FF1, will only be cleared when the tem-
perature drops below the recovery level defined by T
No circuitry will be disabled. External control circuits must take
action to limit the power dissipation in some way so as to prevent
overtemperature damage to the A3941 chip and unpredictable
device operation.
VREG Undervoltage
and the bootstrap charge current. It is critical to ensure that the
voltages are sufficiently high before enabling any of the outputs.
If the voltage at VREG, V
undervoltage lockout threshold, V
enter the VREG undervoltage fault state. In this fault state, both
FF1 and FF2 will be high, and the outputs will be disabled. The
VREG undervoltage fault state and the fault flags will be cleared
when V
threshold, V
The VREG undervoltage monitor circuit is active during pow-
er-up, and the A3941 remains in the VREG undervoltage fault
state until V
lockout threshold, V
*Yes indicates all gate drives low, and all FETs off.
High
High
High
High
Low
Low
Low
Low
FF1
Flag State
REG
High
High
High
High
High
High
FF2
Low
Low
rises above the rising VREG undervoltage lockout
REG
REGUVon
No fault
Short-to-ground
Short-to-supply
Shorted load
Overtemperature
V5 undervoltage
VREG undervoltage
Bootstrap undervoltage
is greater than the rising VREG undervoltage
Fault Description
If the junction temperature exceeds the over-
.
REGUVon
VREG supplies the low-side gate driver
REG
.
, drops below the falling VREG
REGUVoff
Outputs*
Disable
, then the A3941 will
Yes
Yes
Yes
Yes
Yes
Yes
No
No
Automotive Full Bridge MOSFET Driver
JF
Latched
Fault
– T
Yes
Yes
Yes
Yes
No
No
No
–
JFhys
.
Bootstrap Capacitor Undervoltage
voltage across the individual bootstrap capacitors to ensure they
have sufficient charge to supply the current pulse for the high-
side drive. Before a high-side drive can be turned on, the voltage
across the associated bootstrap capacitor must be higher than the
turn-on voltage limit. If this is not the case, then the A3941 will
start a bootstrap charge cycle by activating the complementary
low-side drive. Under normal circumstances, this will charge the
bootstrap capacitor above the turn-on voltage in a few microsec-
onds and the high-side drive will then be enabled.
The bootstrap voltage monitor remains active while the high-side
drive is active and, if the voltage drops below the turn-off volt-
age, a charge cycle is initiated.
In either case, if there is a fault that prevents the bootstrap capaci-
tor charging, then the charge cycle will timeout, the fault flags
(indicating an undervoltage) will be set, and the outputs will be
disabled. The bootstrap undervoltage fault state remains latched
until RESET is set low.
V5 Undervoltage
age at V5 is monitored to ensure correct logical operation. If
the voltage at V5, V
lockout threshold, V
undervoltage fault state. In this fault state, both FF1 and FF2 will
be high, and the outputs will be disabled. In addition, because
the state of other reported faults cannot be guaranteed, all fault
states and fault flags are reset and replaced by the fault flags cor-
responding to a V5 undervoltage fault state. For example, a V5
undervoltage will reset an existing short circuit fault condition
and replace it with a V5 undervoltage fault. The V5 undervoltage
fault state and the fault flags will be cleared when V5 rises above
the rising V5 undervoltage lockout threshold defined by V
+ V
The V5 undervoltage monitor circuit is active during power-up,
and the A3941 remains in the V5 undervoltage fault state until V5
is greater than the rising VREG undervoltage lockout threshold,
V
Short Fault Operation
by monitoring the drain-souce voltage, V
and comparing it to the fault threshold voltage at the VDSTH pin.
Because power MOSFETs take a finite time to reach the rated
on-resistance, the measured drain-source voltages will show a
fault as the phase switches. To avoid such false short fault detec-
5UVoff
5UVhys
+V
.
5UVhys
.
The output of the logic supply regulator volt-
5
5UVoff
, drops below the falling V5 undervoltage
Shorts in the power bridge are determined
, then the A3941 will enter the V5
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
The A3941 monitors the
DS
, of each active FET
5UVoff
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