PM6685 datasheet(48/52 Pages) STMICROELECTRONICS

48 / 52 page

Design example

PM6685

48/52

Figure 41. Current paths, ground connection and driver traces layout

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As general rule, make the high side and low side drivers traces wide and short.

The high side driver is powered by the bootstrap circuit. It’s very important to place

capacitor CBOOT and diode DBOOT as near as possible to the HGATE pin (for

example on the layer opposite to the device). Route HGATE and PHASE traces as near

as possible in order to minimize the area between them.

The Low side gate driver is powered by the 5V linear regulator output. Placing PGND

and LGATE pins near the low side MOSFETs reduces the length of the traces and the

crosstalk noise between the two sections.

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The linear regulator outputs are referred to SGND as long as the reference voltage

Vref. Place their output filtering capacitors as near as possible to the device.

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Place input filtering capacitors near VCC and VIN pins.

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It would be better if the feedback networks connected to COMP and OUT pins are

“referred” to SGND in the same point as reference voltage Vref. To avoid capacitive

coupling place these traces as far as possible from the gate drivers and phase

(switching) paths.

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Place the current sense traces on the bottom side. Use a dedicated connection

between the switching node and the current limit resistor RCSENSE.

PM6685 Datasheet(PDF) 48 Page - STMicroelectronics