A3955 Allegro MicroSystems, Inc., A3955 Datasheet - Page 10

• Manufacturer Part Number: A3955
• Description: Full-Bridge PWM Microstepping Motor Driver
• Manufacturer: Allegro MicroSystems, Inc.

A3955
Thermal Considerations.
turns off all output transistors when the junction temperature
reaches approximately +165°C. This is intended only to protect
the device from failures due to excessive junction temperatures
and should not imply that output short circuits are permitted. The
output transistors are re-enabled when the junction temperature
cools to approximately +150°C.
Stepper Motor Applications.
optimize performance in microstepping/sinusoidal stepper-motor
PHASE
V
V
+5 V
D 2A
PFD
REF
A
1
2
3
5
6
7
8
4
BRIDGE A
LOGIC
Thermal-protection circuitry
The A3955 is used to
Full-Bridge PWM Microstepping Motor Driver
Figure 5 — Microstepping/Sinusoidal Drive Current
MIXED DECAY
16
15
14
13
12
11
10
11
9
Figure 4 — Typical Application
V
BB
SLOW DECAY
47 μF
D 0A
D 1A
drive applications (see fi gures 4 and 5). When the load current
is increasing, the slow current-decay mode is used to limit the
switching losses in the driver and iron losses in the motor. This
also improves the maximum rate at which the load current can
increase (as compared to fast decay) due to the slow rate of
decay during t
current-decay mode is used to regulate the load current to the
desired level. This prevents tailing of the current profi le caused
by the back-EMF voltage of the stepper motor (see fi gure 3A).
MIXED DECAY
D 1B
D 0B
V
47 μF
BB
OFF
SLOW DECAY
10
11
12
13
14
15
16
9
. When the load current is decreasing, the mixed
BRIDGE B
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
LOGIC
Dwg. WK-004-3
8
7
6
5
4
3
2
1
Dwg. EP-047-3
D 2B
PHASE
+5 V
V
V
REF
PFD
B
10