A4970 データシートの表示（PDF） - Allegro MicroSystems

部品番号

コンポーネント説明

一致するリスト

A4970

Dual Full-Bridge PWM Motor Driver

Allegro MicroSystems 

A4970

Dual Full-Bridge Motor Driver

APPLICATION NOTES

Current Sensing

To minimize current sensing inaccuracies caused by ground trace

IR drops, each current-sensing resistor should have a separate

return to the ground terminal of the device. For low-value sense

resistors, the IR drops in the PCB can be significant and should

be taken into account. The use of sockets should be avoided as

their contact resistance can cause variations in the effective value

of RS.

Generally, larger values of RS reduce the aforementioned effects

but can result in excessive heating and power loss in the sense

resistor. The selected value of RS should not cause the maximum

operating voltage of 0.75 V (VREF(max)/10), for the VE terminal,

to be exceeded. The recommended value of RS is in the range of:

RS = 0.50 / ITRIP(max) .

If desired, the reference input voltage can be filtered by placing

a capacitor from VREF to ground. The ground return for this

capacitor as well as the bottom of any resistor divider used

should be independent of the high-current power-ground trace to

avoid changes in VREF due to IR drops.

Thermal Considerations

For normal operation it is recommended that the maximum

operating junction temperature be 145°C, which is below the

operating range of the TSD system. The junction temperature can

be measured best by attaching a thermocouple to the batwing of

the device and measuring the tab temperature, TTAB. The junction

temperature can then be approximated by using the formula:

TJ = TTAB + (2 × ILOAD × VF × RθJT) ,

where VF can be chosen from the electrical specification table

for the given level of ILOAD. The value for RθJT is approximately

6°C/W.

The power dissipation of the batwing package can be improved

20% to 30% by adding a section of printed circuit board copper

(typically 6 to 18 square centimeters) connected to the batwing

terminals of the device.

The thermal performance in applications that run at high load

currents, high duty cycles, or both, can be improved by adding

external diodes from each output to ground in parallel with the

internal diodes. Fast-recovery (≤200 ns) diodes should be used to

minimize switching losses.

Load Supply Terminal

The load supply terminal, VBB, should be decoupled with an

electrolytic capacitor (≥47 μF is recommended), placed as close

to the device as is physically practical. To minimize the effect of

system ground IR drops on the logic and reference input signals,

the system ground should have a low-resistance return to the load

supply voltage.

Fixed Off-Time Selection

With increasing values of tOFF, switching losses decrease, low-

level load current regulation improves, EMI reduces, PWM

frequency decreases, and ripple current increases. The value of

tOFF can be chosen for optimization of these parameters. For

applications where audible noise is a concern, typical values of

tOFF should be chosen in the range of 15 to 35 μs.

Allegro MicroSystems, Inc.

7

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Share Link: