MCP14700 datasheet(14/26 Pages) MICROCHIP

14 / 26 page

MCP14700

DS22201A-page 14

5.4

PCB Layout

Proper PCB layout is important in a high current, fast

switching circuit to provide proper device operation.

Improper component placement may cause errant

switching, excessive voltage ringing, or circuit latch-up.

There are two important states of the MCP14700

outputs, high and low. Figure 5-1 depicts the current

flow paths when the outputs of the MCP14700 are high

and the power MOSFETs are turned on. The charge

needed to turn on the low-side power MOSFET comes

from the decoupling capacitor CVCC. The current flows

from this capacitor through the internal LOWDR

circuitry, into the gate of the low-side power MOSFET,

out the source, into the ground plane, and back to

CVCC. To reduce any excess voltage ringing or spiking,

the inductance and area of this current loop must be

minimized.

FIGURE 5-1:

Turn On Current Paths.

The charge needed to turn on the high-side power

MOSFET comes from the bootstrap capacitor CBOOT.

Current flows from CBOOT through the internal

HIGHDR circuitry, into the gate of the high-side power

MOSFET, out the source and back to CBOOT. The

printed circuit board traces that construct this current

loop need to have a small area and low inductance. To

control the inductance, short and wide traces must be

used.

Figure 5-2 depicts the current flow paths when the

outputs of the MCP14700 are low and the power

MOSFETs are turned off. These current paths should

also have low inductance and a small loop area to

minimize the voltage ringing and spiking.

FIGURE 5-2:

Turn Off Current Paths.

The following recommendations should be followed for

optimal circuit performance:

- The components that construct the high

current paths previously mentioned should be

placed close the MCP14700 device. The

traces used to construct these current loops

should be wide and short to keep the

inductance and impedance low.

- A ground plane should be used to keep both

the parasitic inductance and impedance

minimized. The MCP14700 device is capable

of sourcing and sinking high peaks current

and any extra parasitic inductance or

impedance will result in non-optimal

performance.

VCC

PWMHI

CVCC

CBOOT

VSUPPLY

MCP14700

PWMLO

VCC

PWMHI

CVCC

CBOOT

VSUPPLY

MCP14700

PWMLO

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