A3941KLPTR-T Allegro Microsystems Inc, A3941KLPTR-T Datasheet - Page 16

• Manufacturer Part Number: A3941KLPTR-T
• Description: IC,Motor Controller,TSSOP,28PIN
• Manufacturer: Allegro Microsystems Inc

Specifications of A3941KLPTR-T

• Configuration: H Bridge
• Input Type: PWM
• Delay Time: 90ns
• Number Of Configurations: 1
• Number Of Outputs: 4
• Voltage - Supply: 5.5 V ~ 50 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Number Of Drivers: 4
• Driver Configuration: Non-Inverting
• Driver Type: High and Low Side
• Rise Time: 35ns
• Fall Time: 20ns
• Propagation Delay Time: 150ns
• Operating Supply Voltage (max): 50V
• Operating Supply Voltage (min): 5.5V
• Operating Temp Range: -40C to 150C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 28
• Package Type: TSSOP EP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Peak: -
• High Side Voltage - Max (bootstrap): -
• Lead Free Status / Rohs Status: Compliant
• Other names: 620-1236-2

A3941
voltage of the Zener diodes between the Cx and Sx pins. In most
applications, with a good ceramic capacitor the working voltage
can be limited to 16 V.
Bootstrap Charging
It is good practice to ensure the high-side bootstrap capacitor is
completely charged before a high-side PWM cycle is requested.
The time required to charge the capacitor, t
approximated by:
where C
∆V is the required voltage of the bootstrap capacitor.
At power-up and when the drives have been disabled for a long
time, the bootstrap capacitor can be completely discharged. In
this case ∆V can be considered to be the full high-side drive
voltage, 12 V. Otherwise, ∆V is the amount of voltage dropped
during the charge transfer, which should be 400 mV or less.
The capacitor is charged whenever the Sx pin is pulled low and
current flows from VREG through the internal bootstrap diode
circuit to C
Bootstrap Charge Management
The A3941 provides automatic bootstrap capacitor charge
management. The bootstrap capacitor voltage for each phase
is continuously checked to ensure that it is above the bootstrap
under-voltage threshold, V
age drops below this threshold, the A3941 will turn on the neces-
sary low-side FET, and continue charging until the bootstrap
capacitor exceeds the undervoltage threshold plus the hysteresis,
V
7 μs, but may be longer for very large values of bootstrap capaci-
tor (>1000 nF). If the bootstrap capacitor voltage does not reach
the threshold within approximately 200 μs, an undervoltage fault
will be flagged.
VREG Capacitor Selection
The internal reference, VREG, supplies current for the low-side
gate drive circuits and the charging current for the bootstrap
BOOTUV
BOOT
+ V
BOOT
BOOTUVhys
is the value of the bootstrap capacitor, in nF, and
.
t
CHARGE
. The minimum charge time is typically
BOOTUV
=
C
BOOT
100
. If the bootstrap capacitor volt-
× ∆V
CHARGE
,
(μs), is
Automotive Full Bridge MOSFET Driver
(6)
capacitors. When a low-side FET is turned on, the gate-drive
circuit will provide the high transient current to the gate that is
necessary to turn on the FET quickly. This current, which can be
several hundred milliamperes, cannot be provided directly by the
limited output of the VREG regulator, and must be supplied by an
external capacitor connected to VREG.
The turn-on current for the high-side FET is similar in value to
that for the low-side FET, but is mainly supplied by the boot-
strap capacitor. However the bootstrap capacitor must then be
recharged from the VREG regulator output. Unfortunately the
bootstrap recharge can occur a very short time after the low-
side turn-on occurs. This requires that the value of the capacitor
connected between VREG and AGND should be high enough to
minimize the transient voltage drop on VREG for the combina-
tion of a low-side FET turn-on and a bootstrap capacitor recharge.
A value of 20 × C
working voltage will never exceed V
rated as low as 15 V. This capacitor should be placed as close as
possible to the VREG pin.
Supply Decoupling
Because this is a switching circuit, there are current spikes from all
supplies at the switching points. As with all such circuits, the power
supply connections should be decoupled with a ceramic capacitor,
typically 100 nF, between the supply pin and ground. These capaci-
tors should be connected as close as possible to the device supply
pins VBB and V5, and the ground pin, GND.
Power Dissipation
In applications where a high ambient temperature is expected, the
on-chip power dissipation may become a critical factor. Careful
attention should be paid to ensure the operating conditions allow
the A3941 to remain in a safe range of junction temperature.
The power consumed by the A3941, P
given:
P
BIAS
P
D
=
=
P
V
BIAS
BB
BOOT
× I
+ P
BB
is a reasonable value. The maximum
CPUMP
;
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
+ P
SWITCHING
REG
D
, can be estimated by:
, so the capacitor can be
,
(7)
(8)
16