SPF7302 datasheet(13/16 Pages) ALLEGRO

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Full Bridge DC Motor Driver

SPF7302

Thermal Design

Figure 10. Power Dissipation Derating Curve

–40 –20

100

120

140 160

With infinite heatsink

Ambient Temperature, T

A (°C)

Mounted on 1000 mm2 PCB

Exposed copper area

thickness 18 μm

Figure 12. Test PCB Land Pattern

100

1000

Copper Area (mm2)

10000

100000

Exposed copper area

thickness 18 μm

Figure 11. Thermal Resistance versus PCB Copper Area

Approximatepowerdissipation,PD,innormaloperationiscalculated

by equation 1, and the junction temperature, TJ, is estimated by

equation 2 or 3. Figure 13 shows example data of ∆TJversusPD.Note:

a final thermal evaluation should be done under actual application

conditions, taking into account actual PCB and load conditions.

PD ≈ VBB  IBB1  (VsatH  VsatL)  IOM  DON

 (VsatL(H)  VF)  IOM  DOFF

(1)

where:

VBB is the supply voltage (battery voltage),

IBB1 is the circuit current during operation,

VsatH is the high-side saturation voltage,

VsatL is the low-side saturation voltage,

VF is the freewheeling diode forward voltage,

IOM is the motor current,

DON is the IN1 and IN2 duty cycle (proportion on) , and

DOFF is the IN1 and IN2 proportion off (DON + DOFF = 100%).

To calculate TJ:

TJ = RθJA× PD + TA

(2)

TJ = TP + RθJC (3.2°C/W) × PD

(3)

where:

RθJA can be obtained from figure 11, and

TP is the temperature at the exposed thermal pad of the device.

Figure 13. Thermal Performance

125

100

0123

PD (W)

∆TJA on PCB with exposed

copper area = 1000 mm2

∆TJC

Allegro MicroSystems, Inc.

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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