MIC4606 datasheet(27/40 Pages) MICROCHIP

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DS20005604D-page 27

MIC4606

Placement of the decoupling capacitors is critical. The

bypass capacitor for VDD should be placed as close as

possible between the VDD and VSS pins. The bypass

capacitor (CB) for the HB supply pin must be located as

close as possible between the HB and HS pins. The

etch connections must be short, wide and direct. The

use of a ground plane to minimize connection

impedance is recommended. Refer to Section 7.13

“Grounding, Component Placement and Circuit

Layout”

for more information.

The voltage on the bootstrap capacitor drops each time it

delivers charge to turn on the MOSFET. The voltage drop

depends on the gate charge required by the MOSFET.

Most MOSFET specifications specify gate charge versus

VGS voltage. Based on this information, and a recom-

mended ΔVHB of less than 0.1V, the minimum value of

bootstrap capacitance is calculated as:

EQUATION 7-13:

If the high-side MOSFET is not switched, but held in an

ON state, the voltage in the bootstrap capacitor will

drop due to leakage current that flows from the HB pin

to ground. This current is specified in the Electrical

Characteristics

table. In this case, the value of CB is

calculated as:

EQUATION 7-14:

The larger value of CB from Equation 7-13 or 7-14

should be used.

7.11

DC Motor Applications

MIC4606 MOSFET drivers are widely used in DC

motor applications. They address both stepper and

brushed motors in full-bridge topologies. As shown in

Figure 7-9 and Figure 7-10, the driver switches the

MOSFETs at variable duty cycles that modulate the

voltage to control motor speed. The full-bridge topology

allows for bidirectional control.

The MIC4606’s 85V operating voltage offers ample

operating voltage margin to protect against voltage

spikes in the motor drive circuitry. It is good practice to

have at least twice the HV voltage of the motor supply.

The MIC4606’s 85V operating voltage allows sufficient

margin for 12V, 24V and 40V motors.

The MIC4606 is offered in a small 4 mm x 4 mm

16-lead QFN package for applications that are space

constrained. The motor trend is to put the motor control

circuit inside the motor casing, which requires small

packaging because of the size of the motor.

The MIC4606 offers low UVLO threshold and program-

mable gate drive, which allows for longer operation

time in battery-operated motors, such as power hand

tools.

QGATE

V

-----------------



Where:

QGATE = Total Gate Charge at VHB

ΔVHB = Voltage Drop at the HB Pin

IHBS tON



V

--------------------------



Where:

IHBS = Maximum HB Pin Leakage Current

tON = Maximum High-Side FET On-Time

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