MP9943 – 36V, 3A PEAK SYNCHRONOUS STEP-DOWN CONVERTER

MP9943 Rev.1.1

www.MonolithicPower.com

17

7/4/2017

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2017 MPS. All Rights Reserved.





D=

IN

OUT

V

V

>65%

In these cases, if BST voltage insufficient

happens, the output ripple voltage may become

extremely large at light load condition, add an

BST pin, as shown in Figure 7.

Figure 7: Optional External Bootstrap Diode to

Enhance Efficiency

The recommended external BST diode is

1N4148, and the BST capacitor value is 0.1µF to

1μF.

PCB layout, especially the input capacitor and

VCC capacitor placement, is very important to

achieve stable operation. For the best results,

follow these guidelines:

1) Place the ceramics input capacitor as close to

IN and GND pins as possible, especially the

small package size (0603) input bypass capacitor.

Keep the connection of input capacitor and IN pin

as short and wide as possible.

2) Place the VCC capacitor to VCC pin and GND

pin as close as possible. Make the trace length of

VCC pin-VCC capacitor anode-VCC capacitor

cathode-chip GND pin as short as possible.

3) Use large ground plane directly connect to

GND pin. Add vias near the GND pin if bottom

layer is ground plane.

4) Route SW, BST away from sensitive analog

areas such as FB.

5) Place the T-type feedback resistor close to

chip to ensure the trace which connects to FB pin

as the short as possible.

Notes:

8) The recommended layout is based on the Figure 9 Typical

Application circuit on page 19.

Top Layer

Bottom Layer

Figure 8: Recommended PCB Layout