MCP8021 datasheet(18/66 Pages) MICROCHIP

18 / 66 page

MCP8021/2

DS20006265D-page 18

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3.11

High-Side N-MOSFET Gate Driver

Outputs (HSA, HSB, HSC)

High-side N-channel MOSFET gate drive signal. Con-

nect to the gate of the external MOSFETs. A resistor

and gate-to-source capacitor may be used between

these pins and the MOSFET gates to limit phase node

slew rate and MOSFET current.

3.12

Bootstrap Inputs (VBA, VBB, VBC)

High-side MOSFET driver bias. Connect these pins

between the bootstrap charge pump diode cathode

and the bootstrap charge pump capacitor. The VBOOT

output is used to provide the bootstrap supply voltage

at the diode anodes. The phase signals are connected

to the other side of the bootstrap charge pump capaci-

tors. The bootstrap capacitors charge to VBOOT when

the phase signals are pulled low by the low-side

drivers. When the low-side drivers turn off and the

high-side drivers turn on, the phase signal is pulled to

VDD, causing the bootstrap voltage to rise to

VDD +12V.

3.13

Low-Side N-MOSFET Gate Driver

Outputs (LSA, LSB, LSC)

Low-side N-channel MOSFET drive signal. Connect to

the gate of the external MOSFETs. A resistor and gate-

to-source capacitor may be used between these pins

and the MOSFET gates to limit current and slew rate.

3.14

Bootstrap Supply (VBOOT)

Bootstrap supply voltage regulator output. The VBOOT

regulator output may be used to power external devices,

such as Hall effect sensors or amplifiers. The regulator

output requires an output capacitor for stability. The pos-

itive side of the output capacitor should be physically

located as close to the VBOOT pin as is practical. A mini-

mum capacitance of 4.7 µF is required to ensure stable

operation of the VBOOT circuit. Larger capacitances may

be used to increase transient performance. The VBOOT

regulator is supplied by the internal charge pump when

the charge pump is active. When the charge pump is

inactive, the VBOOT regulator is supplied by VDD.

The type of capacitor used may be ceramic, tantalum

or aluminum electrolytic. The low-ESR characteristics

of the ceramic will yield better noise and PSRR

performance at high frequency.

3.15

+3.3V or +5V LDO (VREG)

The VREG pin may be a +3.3V or a +5V Low Dropout

(LDO) voltage regulator output, depending on device

part number. The VREG LDO may be used to power

external devices, such as Hall effect sensors, amplifiers

or host processors. The VREG LDO is enabled when the

device is not in Sleep mode. The LDO requires an out-

put capacitor for stability. The positive side of the output

capacitor should be physically located as close to the

VREG pin as is practical. For most applications, a mini-

mum 4.7 µF of capacitance will ensure stable operation

of the LDO circuit. Larger capacitances may be used to

increase transient performance.

The type of capacitor used may be ceramic, tantalum

or aluminum electrolytic. The low-ESR characteristics

of the ceramic will yield better noise and PSRR

performance at high frequency.

3.16

Power Supply Input (VDD)

Connect VDD to the main supply voltage. This voltage

should be the same as the motor voltage. The driver

overcurrent feature is relative to the VDD pin. When the

VDD voltage is separate from the motor voltage, the

overcurrent protection feature may not be available.

The VDD voltage must not exceed the maximum operat-

ing limits of the device. Connect a bulk capacitor close

to this pin for good load step performance and transient

protection. The actual capacitance should be equal to

or larger than the sum of the capacitors attached to the

driver supply outputs. The attached capacitors are the

VREG, VBOOT and VBx (three bootstrap capacitors), and

the charge pump capacitances.

EQUATION 3-1:

VDD BULK CAPACITOR

CALCULATION

The type of capacitor used may be ceramic, tantalum

or aluminum electrolytic. The low-ESR characteristics

of the ceramic will yield lower voltage drop, better

noise and PSRR performance at high frequency.

3.17

Charge Pump Flying Capacitor

(CAP1, CAP2)

Charge pump flying capacitor connection. Connect the

charge pump capacitor across these two pins. The

Charge Pump Flying Capacitor, CCP, supplies the

power for the VBOOT voltage regulator when the

charge pump is active.

A Schottky diode between the CAP1 pin and HVSS is

recommended to ensure that the CAP1 pin absolute

minimum voltage specification is maintained.

CVDD CVREG + CVBOOT + (3  CVBX) + CCAPx

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