A3980 Allegro MicroSystems, Inc., A3980 Datasheet - Page 13

• Manufacturer Part Number: A3980
• Description: Automotive DMOS Microstepping Driver with Translator
• Manufacturer: Allegro MicroSystems, Inc.

The A3980 is a power circuit, therefore careful consider-
ation must be given to power dissipation and the effects
of high currents on interconnect and supply wiring.
Power Dissipation. A fi rst order approximation of
the power dissipation in the A3980 can be determined
by examining the power dissipation in each of the
two full-bridges during each of the operation modes.
When synchronous rectifi cation is used, current fl ow
most of the time through the DMOS FETs that are
switched on. When synchronous rectifi cation is not
used, the current fl ows through the body diode of
the DMOS FETs during the decay phase. The use of
fast or slow decay also affects the dissipation. All the
above combinations can be calculated from fi ve basic
DMOS output states, shown in the following illustrations.
Both low-side DMOS output
transistors are on. Current circu-
lates through both transistors and
the load.
Dissipation is I
DMOS transistors:
Diagonally opposite DMOS output
transistors are on. Current fl ows
from ground through load to posi-
tive supply.
Dissipation is I
DMOS transistors:
P
Synchronous Slow Decay
Synchronous Fast Decay
SF
P
= I
SS
2
= I
(R
2
DSONH
(2
2
2
×
R losses in the
R losses in the
R
+ R
DSONL
DSONL
)
Automotive DMOS Microstepping Driver with Translator
)
Application Information
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www.allegromicro.com
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
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One low-side DMOS output tran-
sistor and one body diode conduct-
ing. Current circulates through the
diode, the transistor, and the load.
Dissipation is I
DMOS transistors plus IV loss in
the diode:
Diagonally opposite body diodes
conducting. Current fl ows from
ground through load to positive
supply.
Dissipation is IV losses in the
diodes:
Diagonally opposite DMOS
output transistors are on. Cur-
rent fl ows from positive supply
through load to ground. Used in
all combinations.
Dissipation is I
DMOS transistors:
Non-Synchronous Slow Decay
P
Non-Synchronous Fast Decay
NS
P
D
= (I
Drive Current Ramp
= I
P
NF
2
2
×
(R
= I (V
R
DSONH
DSONL
2
R losses in the
2
R losses in the
FH
A3980
+ R
+ V
) + (I
DSONL
Fl
)
×
V
)
F
13
)