A4980LP View Datasheet(PDF) - Allegro MicroSystems
Part Name
Description
MFG CO.
'A4980LP' PDF : 44 Pages View PDF
A4980
Automotive, Programmable Stepper Driver
The total power dissipation for each of the four decay modes,
PD(TOT) XX, is the average power for the drive current ramp por-
tion, PD , and the drive current decay portion, PD(XX) of the PWM
cycle. For slow decay the current will be rising for approximately
20% of the cycle and decaying for approximately 80%. For fast
decay the ratio will be approximately 50%. Note that these are
approximate figures and will vary slightly depending on the
motor characteristics and the use of synchronous rectification.
The following formulas may be used to estimate total power dis-
sipation:
• Synchronous slow decay mode
PD(TOT)SS = 0.2 × PD + 0.8 × PD(SS)
PD(TOT)SS = 0.2 (I 2 [RDS(on)H + RDS(on)L ]) + 0.8 (I 2 × 2 × RDS(on)L)
• Non-synchronous slow decay mode
PD(TOT)NS = 0.2 × PD + 0.8 × PD(NS)
PD(TOT)NS = 0.2(I2[RDS(on)H+RDS(on)L])+0.8(I2×RDS(on)L+I ×VF)
• Synchronous fast decay mode
PD(TOT)SF = 0.5 × PD + 0.5 × PD(SF)
PD(TOT)SF = I 2 (RDS(on)H + RDS(on)L )
• Non-synchronous fast decay mode
PD(TOT)NF = 0.5 × PD + 0.5 × PD(NF)
PD(TOT)NF = 0.5( I 2 [RDS(on)H + RDS(on)L ] ) + 0.5( I × [VFH + VFL ] )
An approximation of the total dissipation can be calculated by
summing the total power dissipated in both bridges and adding
the control circuit power due to VBB × IBB and VDD × IDD .
The total power at the required ambient temperature can then be
compared to the allowable power dissipation shown in figure 17.
For critical applications, where the first order power estimate is
close to the allowable dissipation, the power calculation should
take several other parameters into account including: motor
parameters, dead time, and switching losses in the controller.
5
4
3
RθJA = 28 °C/W
(on 4-layer PCB)
2
1
RθJA = 32 °C/W
(on 2-layer PCB)
0
25
50
75
100
125
150
Ambient Temperature (°C)
Figure 17. Allowable power dissipation, on typical PCBs
Allegro MicroSystems, Inc.
32
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Share Link: 
