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

MP6528 Rev. 1.03

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14

6/20/2017

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the minimum bootstrap capacitance can be

in nF.

The bootstrap capacitors should not

exceed 1µF, or they may cause improper

operation at start-up.

For

most

applications,

bootstrap

capacitors

between 0.1µF and 1µF, X5R or X7R ceramic,

rated for 25V minimum, are recommended.

The VREG pin requires a bypass capacitor to

ground of 10µF. This should be an X7R or X5R

ceramic capacitor rated for 16V minimum.

VIN requires a bypass capacitor to ground,

placed as close as possible to the device. At a

minimum, a 0.1µF X5R or X7R ceramic capacitor,

rated for the VIN voltage, is recommended.

Depending on the power supply impedance and

the distance between the MOSFETs and the

power supply, additional bulk capacitance is

usually needed.

Between 47µF and 470µF of

low ESR electrolytic capacitors are typically used.

Dead Time Resistor Selection

During the transition between driving an output

low and high, there is a short period when neither

the HS nor LS MOSFET is turned on.

This

period, called “dead time”, is needed to prevent

any overlap in conduction between HS and LS

MOSFETs, which would effectively provide a

short-circuit directly between the power supply

and ground.

This condition, referred to as

“shoot-through”, causes large transient currents,

and can destroy the MOSFETs.

Since motors are inductive by nature, once

current is flowing in the motor, it cannot stop

immediately, even if the MOSFETs are turned off.

This “recirculation current” continues to flow in

the original direction until the magnetic field has

decayed.

When the MOSFETs are turned off, this current

will flow through the “body diode” which is

inherent in the MOSFET device.

MOSFET body diodes have a much higher

voltage drop than the MOSFET has during

conduction, so there more power dissipated in

body diode conduction than during the on time.

Because of this, it is desirable to minimize the

dead time.

However, the dead time must be

made large enough to guarantee under all

conditions that the HS and LS MOSFETs are

never turned on at the same time.

Dead time can be set over a large range, by

selecting the value of the external resistor that is

connected to the DT pin. Usually, a good starting

point is a dead time of about 1µS, which requires

a 200k resistor on the DT pin. If faster switching

and/or a high PWM frequency (over ~30kHz) is

used, shorter dead time may be desirable; if

switching is slowed using external gate resistors,

longer dead time may be needed.

The waveform below shows about a 300nS dead

time between the LS gate turn-off and the HS

gate turn-on.

LSS Resistor Selection

If the voltage applied to the LSS pin ever

exceeds 500mV, an overcurrent event will be

recognized. The external sense resistor is sized

to provide less than 500mV drop at the maximum

expected motor current. For example, if a 50 mΩ

resistor is used, a current of 10 amps would

cause

a

500mV

drop,

and

activate

the

overcurrent protection.

If this function is not needed, connect LSS

directly to ground.

OCREF Voltage Selection

An internal comparator compares the voltage

drop across each MOSFET with a voltage that is

externally provided on the OCREF input pin.

This voltage is normally provided by an external

resistor divider from a convenient power supply.

If the drop across any MOSFET ever exceeds

the voltage on the OCREF pin, a short-circuit

event is recognized.

If this function is not needed, connect OCREF to

VREG through a 100k resistor.