MP6528 – 5V TO 60V, H-BRIDGE GATE DRIVER

MP6528 Rev. 1.03

www.MonolithicPower.com

13

6/20/2017

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APPLICATIONS INFORMATION

VIN Input Voltage

The VIN pin supplies all power to the device. It

must be properly bypassed with a capacitor to

ground

–

see

below

for

specific

recommendations.

The normal operating range of VIN is between

5V and 60V.

VIN should never be allowed to exceed the

absolute maximum ratings, even in a short term

transient condition, or damage to the device may

result.

In some cases

– especially where

mechanical energy can turn a motor into a

generator

– it may be necessary to use some

form of overvoltage protection, such as a TVS

diode, between VIN and ground.

Component Selection

MOSFET selection

Correctly selecting the power MOSFETs used to

drive a motor is crucial to designing a successful

motor drive.

The first requirement is that the MOSFET must

have a VDS breakdown voltage that is higher

than the supply voltage. It is recommended that

considerable margin

– 10-15 volts - be added to

prevent

MOSFET

damage

from

transient

voltages

that

can

be

caused

by

parasitic

inductances in the PCB layout and wiring. For

example, for 24V power supply applications,

MOSFETs having a breakdown voltage of 40V-

60V minimum are recommended. More margin

is desirable in high current applications, as the

transients caused by parasitic inductances may

be larger.

Also, there are conditions like

regenerative braking that can inject current back

into the power supply; care must be taken that

this does not cause an increase in the power

supply

voltage

large

enough

to

damage

components.

The MOSFETs must be able to safely pass the

current needed to run the motor.

The highest

current condition, which is normally when the

motor is first started or stalled, needs to be

supported.

This is typically called the “stall

current” of the motor.

Related to the current capability of the MOSFET

is the rds(on).

This is the resistance of the

MOSFE

T when it is in the fully “turned on” state.

The MOSFET will dissipate power proportional to

the rds(on) and the motor current: P=I

rds(on) needs to be selected so that for the

desired motor current, the heat generated in this

power can be safely dissipated. In some cases,

this

may

require

special

PCB

design

considerations and/or external heatsinks to be

used for the MOSFETs.

Some consideration should be made for the safe

operating area (SOA) of the MOSFETs in fault

conditions, such as a short circuit. The IC will act

quickly in the event of a short, but there is still a

very short time (on the order of 3µS) where large

currents can flow in the MOSFETs while the

protection circuits recognize the fault and disable

the outputs.

External Capacitor Selection

The MP6528 has a unique feature in that it can

provide a gate drive voltage (VREG) of 10-12V

even if the input supply voltage drops as low as

5V.

This gate drive voltage is generated by a

charge pump inside the part, which uses external

capacitors.

have a capacitance of 470nF.

It needs to be

rated to withstand the maximum VIN power

supply voltage.

An X7R or X5R ceramic

capacitor is recommended.

With a 470nF

capacitor, VREG can output approximately 10mA

when VIN is 5V. If operation below 10V is not

needed, a 220nF capacitor can be used

To provide the large peak currents needed to

turn on the HS MOSFET, bootstrap capacitors

are used.

These capacitors are charged when

the output is driven low, then the charge in the

bootstrap capacitor is used to turn on the HS

MOSFET when the output is driven high. (Note

that an internal charge pump will keep the

bootstrap capacitor changed when the output is

held high for an extended period).

The bootstrap capacitors are selected depending

on the MOSFET total gate charge. When the HS

MOSFET is turned on, the charge stored in the

bootstrap capacitor is transferred to the HS

MOSFET gate. As a simplified approximation,