MP9840 – 36V, 3.5A, LOW IQ, SYNC STEP-DOWN CONVERTER

PIN FUNCTIONS

Pin #

QFN-16

(3mmx4mm)

Name

Description

1

PHASE

Selectable in-phase or 180° out-of-phase of SYNC input. Pull PHASE high to be

in-phase. Pull PHASE low to be 180° out-of-phase.

2

VIN

Input supply. VIN supplies power to all of the internal control circuitries and the

power switch connected to SW. Place a decoupling capacitor to ground close to VIN

to minimize switching spikes.

3, 10

SW

Switch node. SW is the output of the internal power switch.

4, 9

PGND

Power ground. PGND is the reference ground of the power device and requires

careful consideration during PCB layout. For best results, connect PGND with

copper pours and vias.

5

EN

Enable. Pull EN below the specified threshold to shut the chip down. Pull EN above

the specified threshold to enable the chip.

6

SYNC

Synchronize. Apply a 350kHz to 2.5MHz clock signal to SYNC to synchronize the

internal oscillator frequency to the external clock. The external clock should be at

least 250kHz larger than the RFREQ set frequency. SYNC can also be used to select

forced CCM or AAM. Drive SYNC high before the chip starts up to choose forced

CCM; drive SYNC low or leave SYNC floating to choose AAM.

7

PG

Power good output. The output of PG is an open drain.

8

BIAS

Bias input. Connect BIAS to an external power supply (5V

≤ V

BIAS

≤ 18V) to reduce

power dissipation and increase efficiency. If not in use, float BIAS or connect BIAS

to ground.

11

BST

Bootstrap. BST is the positive power supply for the high-side MOSFET driver

connected to SW. Connect a bypass capacitor between BST and SW.

12

VCC

Bias supply. VCC supplies power to the internal control circuit and gate drivers. A

decoupling capacitor (

≥1µF) to ground is required close to VCC.

13

AGND

Analog ground. AGND is the reference ground of the logic circuit.

14

SS

Soft-start input. Place a capacitor from SS to AGND to set the soft-start period. The

MP9840 sources 10µA from SS to the soft-start capacitor during start-up. As the SS

voltage rises, the feedback threshold voltage increases to limit inrush current during

start-up.

15

FB

Feedback input. Connect FB to the center point of the external resistor divider. The

feedback threshold voltage is 0.8V. Place the resistor divider as close to FB as

possible. Avoid placing vias on the FB traces.

16

FREQ

Switching frequency program. Connect a resistor from FREQ to ground to set the

switching frequency.

MP9840 Rev. 1.01

www.MonolithicPower.com

15

1/23/2018

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