MP8869W datasheet(35/41 Pages) MPS

35 / 41 page

MP8869W

– 3V - 18V, 12A, SYNCHRONOUS STEP-DOWN CONVERTER

MP8869W Rev. 1.02

www.MonolithicPower.com

1/18/2018

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

External Bootstrap Diode

An external bootstrap diode can enhance the

efficiency of the regulator given the following

conditions:

 VOUT is 5V or 3.3V

 Duty cycle is high: D > 50%

In these cases, add an external BST diode from

VCC to BST (see Figure 13).

MP8869W

Figure 13: Optional External Bootstrap Diode to

Enhance Efficiency

The recommended external BST diode is IN4148,

and the recommended BST capacitor value is

0.1ST to 1cap

Connect VCC to VIN at a Low Input

Voltage

VCC can be connected to VIN directly when VIN

is lower than 3.5V. This helps improve the

MP8869W’s

low

input

voltage

efficiency

performance. To use this application set-up, the

VIN spike voltage must be limited below 4V,

otherwise VCC may be damaged.

PCB Layout Guidelines (9)

Efficient

PCB

layout

critical for

stable

operation. For best results, refer to Figure 14 and

follow the guidelines below. A four-layer layout is

strongly recommended to achieve better thermal

performance.

1. Place the high-current paths (PGND, VIN,

and SW) very close to the device with short,

direct, and wide traces.

2. Keep the VIN and PGND pads connected

with large copper planes.

3. Use at least two layers for the IN and PGND

trace to achieve better thermal performance.

4. Add several vias close to the IN and PGND

pads to help with thermal dissipation.

5. Place the input capacitors as close to VIN

and PGND as possible.

6. Place the decoupling capacitor as close to

VCC and PGND as possible.

7. Place the external feedback resistors next to

FB.

8. Ensure that there is no via on the FB trace.

9. Keep the switching node SW short and away

from the feedback network.

10. Keep the BST voltage path (BST, C3, and

SW) as short as possible.

NOTE:

The recommended layout is based on the Typical Application

circuit on page 34.

MP8869W Datasheet(PDF) 35 Page - Monolithic Power Systems

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