A3981KLPTR-T Allegro Microsystems Inc, A3981KLPTR-T Datasheet - Page 31

• Manufacturer Part Number: A3981KLPTR-T
• Description: AUTOMOTIVE PROGRAMMABLE STEPPER DRVR
• Manufacturer: Allegro Microsystems Inc

Specifications of A3981KLPTR-T

• Applications: Stepper Motor Driver, 2 Phase
• Number Of Outputs: 1
• Voltage - Load: 7 V ~ 28 V
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP (0.173", 4.40mm Width) Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A3981
Layout
Traces
PCB The printed circuit board (PCB, or printed wiring board)
should use a higher weight copper thickness than a standard small
signal or digital circuit board. This helps to reduce the impedance
of the printed traces when conducting high currents. PCB traces
carrying switching currents should be as wide and short as pos-
sible to reduce the inductance of the trace. This will help reduce
any voltage transients caused by current switching during PWM
current control.
For optimum thermal performance, the exposed thermal pad on
the underside of the A3981 should be soldered directly onto the
board. A solid ground plane should be added to the opposite side
of the board, and multiple vias through the board to the ground
plane should be placed in the area under the thermal pad.
Decoupling
All supplies should be decoupled with an electrolytic capacitor in
parallel with a ceramic capacitor. The ceramic capacitor should
have a value of 100 nF and should be placed as close as pos-
sible to the associated supply and ground pins of the A3981. The
electrolytic capacitor connected to VBB should be rated at least
1.5 times the maximum circuit voltage, and selected to support
the maximum ripple current provided to the motor. The value of
the capacitor is unimportant but should be the lowest value with
the necessary ripple current capability.
The pump capacitor between CP1 and CP2, the pump storage
capacitor between VCP and VBB, and the compensation capaci-
tor between VREG and ground should be connected as close as
possible to the respective pins of the A3981.
Grounding
A star ground system, with the common star point located close to
the A3981, is recommended. The reference ground, AGND (pin
7), and the power ground, PGND (pin 21), must be connected
Automotive, Programmable Stepper Driver
together externally. The copper ground plane located under the
exposed thermal pad is typically used as the star ground point.
Current Sense Resistor
In sensing the output current level, to minimize inaccuracies
caused by ground-trace IR drops, the current sense resistor (R
should have an independent ground return to the star ground
point. This path should be as short as possible. For low-value
sense resistors, the IR drop in the PCB trace to the sense resis-
tor can be significant and should be taken into account. Surface
mount chip resistors are recommended to minimize contact
resistance and parasitic inductance. The value, R
resistor is given by:
There is no restriction on the value of R
range of V
teed. However, it is recommended that the value of V
as high as possible to improve the current accuracy. The table
below provides increasing values of I
of V
REF
and standard E96 values of R
REF
over which the output current precision is guaran-
I
(mA)
1008
SMAX
100
200
300
405
501
610
702
812
912
Suggested Values
R
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
S
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.

16
(mΩ)
499
499
417
309
249
205
178
154
137
124
R
V

REF
S
I
SMAX
SMAX
S
.
S
V
(V)
0.8
1.6
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
REF
or V
for suggested values
REF
S
, other than the
, of the sense
REF
be kept
S
)
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