MIC4600 datasheet(16/26 Pages) MICROCHIP

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MIC4600

DS20005584A-page 16

 2016 Microchip Technology Inc.

path for the current is from the source of the MOSFET

and back to capacitor CB. The high-side circuit return

path usually does not have a low-impedance ground

plane so the etch connections in this critical path

should be short and wide to minimize parasitic

inductance. As with the low-side circuit, impedance

between the MOSFET source and the decoupling

capacitor causes negative voltage feedback that fights

the turn-on of the MOSFET.

It is important to note that capacitor CB must be placed

close to the BST and SW pins. This capacitor not only

provides all the energy for turn-on but it must also keep

HB pin noise and ripple low for proper operation of the

high-side drive circuitry.

FIGURE 6-3:

Turn-On Current Paths.

Figure 6-4 shows the critical current paths when the

driver outputs go low and turn off the external

MOSFETs. Short, low-impedance connections are

important during turn-off for the same reasons given in

the turn-on explanation. Current flowing through the

internal diode replenishes charge in the bootstrap

capacitor, CBST.

FIGURE 6-4:

Turn-Off Current Paths.

Use a ground plane to minimize parasitic inductance

and impedance of the return paths. The MIC4600 is

capable of greater than 1A peak currents and any

impedance between the MIC4600, the decoupling

capacitors, and the external MOSFET will degrade the

performance of the driver.

BST

VDD

Level

shift

HSI

LSI

PGND

CVDD

LOW-SIDE DRIVE

TURN-OFF CURRENT PATH

HIGH-SIDE DRIVE

TURN-OFF CURRENT PATH

MIC4600

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