NB681- 28V, 6 A, HIGH-CURRENT SYNCHRONOUS BUCK CONVERTER WITH 2-BIT VID

NB681 Rev. 1.04

www.MonolithicPower.com

7

12/28/2017

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PIN FUNCTIONS

PIN #

Name

Description

1

VIN

Supply voltage input. The NB681 operates from a +4.5 V to +24 V input rail. An input

capacitor is needed to decouple the input rail. Use wide PCB traces and multiple vias to

make the connection with at least two layers for the input trace.

2

PGND

Power ground. Use wide PCB traces and multiple vias to make the connection.

3, 4

C1, C0

2-bit VID control input. Set C1 and C0 with MODE to get different voltage references for

different rails.

5

EN

Enable. Drive EN high to turn on the buck regulator; drive EN low to turn off the buck

regulator. EN determines USM. If EN is within 1.2 V-1.7 V, it is in USM. If EN >2.3 V, it is in

normal mode. For normal mode, it is recommended that EN rising finishes in <1 ms.

6

LP#

Low-power mode control signal. Pull LP# high in normal operation. Pull LP# low to enter

low-power mode. Usually, LP# is controlled by the SLP#S0 of the system.

7

MODE

Selection for VCCIO/PRIMCORE/EDRAM/EOPIO/V1.0 A applications with external 1%

resistors.

8

SW

Switch output. Connect SW to the inductor and bootstrap capacitor. SW is connected to

VIN when the HS-FET is on; SW is connected to PGND when the LS-FET is on. Use wide

and short PCB traces to make the connection. SW is noisy, so keep sensitive traces away

from SW.

9

BST

Bootstrap. A >100 nF capacitor connected between SW and BST is required to form a

floating supply across the high-side switch driver.

10

3V3

External 3V3 VCC input for control and driver. Place a 1 µF decoupling capacitor close to

3V3 and AGND.

11

AGND

Signal logic ground. Make a Kelvin connection to PGND near the VCC capacitor. AGND

can be applied as a remote sense ground with proper setting.

12

VOUT

Output sense input. Connect the VOUT to the remote output capacitor with good GND

decoupling. Keep the VOUT trace away from SW or other noisy nodes. It is recommended

to use a >20 mil trace for the vout sense.

13

PG

Power good output. PG is an open-drain signal. PG is high if the output voltage is higher

than 95 percent of the nominal voltage or lower than 105 percent of the nominal voltage.