AMT49413 datasheet(7/21 Pages) ALLEGRO

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3-Phase BLDC Controller and MOSFET Driver

AMT49413

Allegro MicroSystems, LLC

115 Northeast Cutoff

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

1.508.853.5000; www.allegromicro.com

Basic Operation

The AMT49413 provides commutation and current control for

3-phasebrushlessDC(BLDC)motorswithintegratedHall-

effect sensors. The motor current is provided by an external

3-phase N-channel MOSFET bridge which is controlled by the

AMT49413, using fixed-frequency pulse-width modulation

(PWM). The use of PWM with N-channel MOSFETs provides

the most cost-effective solution for a high-efficiency motor drive.

The AMT49413 provides all the necessary circuits to ensure that

the gate-source voltage of both high-side and low-side external

MOSFETs are above 10 V, at supply voltages down to 7 V. For

extreme battery voltage drop conditions, functional operation

is guaranteed down to 5.5 V but with a reduced gate drive. The

AMT49413 also decodes the commutation sequence from three

Hall-effectsensorsspacedat120°intheelectricalcycle,and

ensures no cross-conduction (shoot-through) in the external bridge.

Individual pins provide direction, brake, and coast control.

Motor current can be sensed by a low-value sense resistor,

RSENSE, in the ground connection to the bridge, amplified and

compared to a reference value. The AMT49413 then limits the

bridge current on a cycle-by-cycle basis. Bridge current can also

be controlled using an external PWM signal with the internal cur-

rent control either disabled or used to set the absolute maximum

motor current. Specific functions are described more fully in the

following sections.

Power Supplies

Only one power connection is required because all internal

circuits are powered by integrated regulators. The main power

supply should be connected to VBB through a reverse battery

protection circuit.

V5 and V5BD A 5 V supply for external pull-up and bias cur-

rents is provided by an integrated 5 V regulator controller and an

external NPN transistor, QV5. The AMT49413 provides the base

drive current on the V5BD pin, and the 5 V reference on the V5

pin. This regulator is also used by the internal logic circuits and

must always be decoupled by at least a 200 nF capacitor, CV5,

between the V5 pin and AGND. For stability, a 100 nF capacitor,

C5BD, also should be connected between V5BD and AGND. If

an external 5 V supply is not required, the V5BD pin and the V5

pin should be connected together.

CP1, CP2, and VREG The gate drive outputs are powered by

an internal charge pump, which requires a pump capacitor, typi-

cally 470 nF, CP, connected between the CP1 and CP2 pins. The

output from the charge pump, 13 V nominal, is used to power

each of the three high- and low-side driver pairs and is also

available on the VREG pin. A sufficiently large storage capaci-

tor, CREG, must be connected to this pin to provide the tran-

sient charging current to the low-side drivers. The charge pump

also provides the charging current for the bootstrap capacitors,

CBOOTx.

An additional “top-off” charge pump is provided for each high-

side drive which allows the high-side drive to maintain the gate

voltage on the external FET indefinitely, ensuring so-called 100%

PWM if required. This is a low-current trickle charge pump

(< 100 µA typical), and is only operated after a high-side driver

has been signaled to turn on. There is a small amount of bias

current (<20 µA) drawn from the Cx pin to operate the floating

high-side circuit, and the charge pump simply provides enough

drive to ensure that the bootstrap voltage, and hence the gate volt-

age, will not droop due to this bias current. The charge required

for initial turn-on of the high-side gate is always supplied by

bootstrap capacitor charge cycles.

Hall-Effect Sensor Inputs

H1,H2,andH3Hall-effectsensorinputsareconfiguredformotors

with120°electrically-spacedHall-effectsensors,butmaybeused

for60°electricalspacingwithanexternalinverter.Hall-effectsen-

sors usually require an additional pull-up resistor to be connected

between the sensor output and 5 V. This 5 V can be provided by

theintegrated5Vregulator.Hall-effectinputshaveahysteresisof

typically 500 mV to reduce the effects of switching noise on the

Hall-effectconnectionstothemotor.Theseinputsarealsofiltered

tofurtherreducetheeffectsofswitchingnoise.TheHall-effect

inputs are pulled-up to 5 V inside the AMT49413 through a high

value(100kΩtypical)resistorinserieswithadiode.Thisinternal

pull-upmakestheHall-effectinputappearhighiftheHallsen-

sorsignalismissing,allowingdetectionofanHall-effectinput

logicfault.TheAMT49413willindicatealogicfaultwhenallHall

inputs are driven to the same logic level. The commutation truth

table for these inputs is shown in Table 2. The inputs can also be

driven directly from a microcontroller or similar external circuit.

Gate Drive

The AMT49413 is designed to drive external N-channel power

MOSFETs. They supply the large transient currents necessary to

quickly charge and discharge the gate capacitance of the external

FETs in order to reduce dissipation in the external FETs during

FUNCTIONAL DESCRIPTION

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