MP8869SGL datasheet(34/39 Pages) MPS

34 / 39 page

MP8869S

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

MP8869S Rev. 1.03

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).

MP8869S

Figure 13: Optional External Bootstrap Diode to

Enhance Efficiency

The recommended external BST diode is

IN4148, and the recommended BST capacitor

value is 0.1µF to 1µF.

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

MP8869S

’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.

four-layer

layout

strongly

recommended

achieve

better

thermal

performance. For best results, refer to Figure

14 and follow the guidelines below.

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 VIN and

PGND trace to achieve better thermal

performance.

4. Add several vias close to the VIN 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

based

the

Typical

Application circuit on page 36 to page 38.

MP8869SGL Datasheet(PDF) 34 Page - Monolithic Power Systems

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