3-Phase BLDC Controller and MOSFET Driver

AMT49413

13

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Power

All supply connections to the AMT49413 should have capaci-

tors mounted between the supply pins and the ground pin. These

capacitors will provide the transient currents which occur during

switching and decouple any voltage transients on the pin from the

main supply.

VBB. Decouple with at least a 100 nF ceramic capacitor mounted

between the VBB pin and the AGND pin. A larger electrolytic

capacitor, typically 10 µF, in parallel with the ceramic capacitor

is also recommended.

VREG. Supplies current for the gate-drive circuit. As the gates

are driven high, they require current from an external capaci-

tor connected to VREG to support the transients. This capacitor

should be placed as close as possible to the VREG pin with the

ground connection close to the AGND pin. Its value should be at

least 20 times larger than the bootstrap capacitor. The capacitor

should have a very low series resistance (ESR) and inductance

(ESL) to avoid large voltage drops during the initial transient.

The optimum capacitor type is a high quality ceramic such as

X7R.However,whentherequiredcapacitanceistoolarge,an

aluminium electrolytic capacitor may be used, with a smaller

ceramiccapacitor(≈100nF)inparallel.

V5. When the 5V regulator is used with an external pass transis-

tor to provide power to other circuits, a 10 µF decoupling capaci-

tor should be connected between the V5 pin and AGND as close

to the pins as possible. If an electrolytic capacitor is used, then a

100 nF ceramic capacitor should be added in parallel. To improve

stability, a 100 nF capacitor also should be connected between

the V5BD pin and AGND. If 5V is not required for external cir-

cuits, the external pass transistor may be omitted, but in that case,

V5 must connected directly to V5BD and decoupled with at least

a 220 nF capacitor between V5 and AGND.

AGND. The AMT49413 has a single ground connection at the

AGND pin. The design ensures that only the operating current

for the controller stage passes through this pin. The charge and

discharge current for the external FETs does not pass though this

pin. The AGND pin is the ground reference for the current trip

It should therefor be kept as quiet as possible. A suggested ground

connection scheme is described in the layout section below.

Power Dissipation. In applications where a high ambient tem-

perature is expected the on-chip power dissipation may become

a critical factor. Careful attention should be paid to ensure the

operating conditions allow the AMT49413 to remain in a safe

range of junction temperature.

using the following formulas:

where N = 2 for slow decay, or N = 4 for fast decay, and

Bootstrap Capacitors

be correctly selected to ensure proper operation of the device. If

the value is too large, time will be wasted charging the capaci-

tor, resulting in a limit on the maximum duty cycle and PWM

frequency. If the value is too small, there can be a large voltage

MOSFET gate.

can be used:

therefore

The voltage drop on the Cx pin as the MOSFET is being turned

on can be approximated by:

Bootstrap Charging. It is good practice to ensure that the

high-side bootstrap capacitor, CBOOT, is completely charged

APPLICATIONS INFORMATION