A4980LP View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A4980LP' PDF : 44 Pages View PDF
A4980
Automotive, Programmable Stepper Driver
Power Dissipation
The A4980 is a power circuit, therefore careful consideration
must be given to power dissipation and the effects of high cur-
rents on interconnect and supply wiring.
A first order approximation of the power dissipation in the A4980
can be determined by examining the power dissipation in each of
the two bridges during each of the operation modes. When syn-
chronous rectification is used current will flow most of the time
through the DMOS transistors that are switched on. When syn-
chronous rectification is not used the current will flow through
the body diode of the DMOS transistors during the decay phase.
The use of fast or slow decay will also affect the dissipation. All
the above combinations can be calculated from five basic DMOS
output states as shown in figure 16.
Synchronous Fast Decay
• Diagonally opposite DMOS output
transistors are on
• Current flows from ground through
load to positive supply
Dissipation is I2R losses in the
DMOS transistors:
PD(SF) = I2 × (RDS(on)H+RDS(on)L )
Non-Synchronous Fast Decay
• Diagonally opposite body diodes
conducting
• Current flows from ground through
load to positive supply
Dissipation is IV losses in the diodes:
PD(NF) = I × ( VFH + VFL )
Synchronous Slow Decay
• Both low-side DMOS output
transistors are on
• Current circulates through both
transistors and the load
Dissipation is I2R losses in the DMOS
transistors:
PD(SS) = I2 × (2 × RDS(on)L )
Non-Synchronous Slow Decay
• One low-side DMOS output transistor
and one body diode conducting
• Current circulates through the diode,
the transistor and the load
Dissipation is I2R losses in the DMOS
transistors plus IV loss in the diode:
PD(NS) = (I2 × RDS(on)L ) ⁄ ( I × VF )
Drive Current Ramp-up
(Used in all combinations)
• Diagonally opposite DMOS output
transistors are on
• Current flows from positive supply
through load to ground
Dissipation is I2R losses in the
DMOS transistors:
PD = I2 × (RDS(on)H + RDS(on)L )
Figure 16. Basic output states
Allegro MicroSystems, Inc.
31
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Share Link: 
