MIC4606 datasheet(30/40 Pages) MICROCHIP

30 / 40 page

MIC4606

DS20005604D-page 30

 2017-2019 Microchip Technology Inc.

7.13

Grounding, Component

Placement and Circuit Layout

Nanosecond switching speeds and ampere peak cur-

rents in and around the MIC4606 driver require proper

placement and trace routing of all components. Improper

placement may cause degraded noise immunity, false

switching, excessive ringing or circuit latch-up.

Figure 7-12 shows the critical current paths of the high

and low-side driver when their outputs go high and turn

on the external MOSFETs. It also helps demonstrate

the need for a low-impedance ground plane. Charge

needed to turn on the MOSFET gates comes from the

decoupling capacitors, CVDD and CB. Current in the

low-side gate driver flows from CVDD through the inter-

nal driver, into the MOSFET gate, and out the source.

The return connection back to the decoupling capacitor

is made through the ground plane. Any inductance or

resistance in the ground return path causes a voltage

spike or ringing to appear on the source of the MOSFET.

This voltage works against the gate drive voltage and

can either slow down or turn off the MOSFET during the

period when it should be turned on.

Current in the high-side driver is sourced from capaci-

tor CB, and flows into the xHB pin and out the xHO pin,

into the gate of the high-side MOSFET. The return 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 xHB and xHS pins. This capacitor not only

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

xHB pin noise and ripple low for proper operation of the

high-side drive circuitry.

FIGURE 7-12:

Turn-On Current Paths.

Figure 7-13 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, CB.

FIGURE 7-13:

Turn-Off Current Paths.

xHS

xHB

xHO

xLO

xHI

xLI

GND

PLANE

GND

PLANE

LOW-SIDE DRIVE TURN-ON

CURRENT PATH

HIGH-SIDE DRIVE

TURN-ON CURRENT

PATH

LEVEL

SHIFT

xHS

xHB

xHO

xLO

xHI

xLI

CVDD

LOW-SIDE DRIVE

TURN-OFF

CURRENT PATH

HIGH-SIDE DRIVE

TURN-OFF CURRENT

PATH

LEVEL

SHIFT

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