MP2229 – 21V, 6A SYNCHRONOUS STEP-DOWN CONVERTER

MP2229 Rev. 1.0

www.MonolithicPower.com

17

2/12/2015

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External Bootstrap Diode

BST voltage may become insufficient at

particular specs (see conditions below). In

these cases an external bootstrap diode can

enhance the efficiency of the regulator at heavy

load and avoid BST voltage insufficiency during

PFM operation at light load. Insufficient BST

voltage is more likely to happen at either of the

following conditions:

large: D=

IN

OUT

V

V

>65%

In these cases (if insufficient BST voltage

occurs), the output-ripple voltage may become

extremely high during a light-load condition.

Add an external BST diode from VCC to BST

(see Figure 9).

FIGURE 9. Optional Bootstrap Diode

The recommended external BST diode is

IN4148, and the BST capacitor is 0.1µF to 1μF.

Efficient PCB layout is critical to achieve stable

operation. For best results, please refer to

Figure 10 and follow the guidelines below:

1) Keep the connection of input ground and

GND as short and wide as possible.

2) Keep the connection of the input capacitor

and IN as short and wide as possible.

3) Ensure all feedback connections are short

and direct. Place the feedback resistors and

compensation components as close to the chip

as possible.

4) Route SW away from sensitive analog areas

(such as FB).

To improve performance, use a 4-layer board.

Figure 10 shows the top and bottom layer of the

PCB (inner 1 and inner 2 are all GND).

Notes:

10)

The recommended layout is based on the Figure 11

“Typical Application Circuit” on Page19.

Top Layer

GND

VCC

Bottom Layer

FIGURE 10. Recommended PCB Layout