RT2855A/B
Functional Pin Description
Pin No.
Pin Name
Pin Function
Feedback Input Voltage. Connect FB to the midpoint of the external feedback
resistive divider to sense the output voltage. Place the resistive divider within
1
FB
5mm from the FB pin. The IC regulates V at 0.765V (typical).
FB
Internal Regulator Output. Connect a 1F capacitor to GND to stabilize
output voltage.
2
VREG5
Soft-Start Control. Connect an external capacitor between this pin and GND
to set the soft-start time.
3
4
5
SS
GND
PGOOD
Ground.
Open Drain Power-good Output. PGOOD connects to PGND whenever VFB
is less than 90% of its regulation threshold (typical).
Enable Control Input. A logic-high enables the converter; a logic-low forces
the IC into shutdown mode reducing the supply current to less than 10A.
6
EN
Power Ground. PGND connects to the source of the internal N-channel
MOSFET synchronous rectifier and to other power ground nodes of the IC.
The exposed pad and the 2 PGND pins should be well soldered to the input
and output capacitors and to a large PCB area for good power dissipation.
7, 8,
PGND
17 (Exposed pad)
Switching Node. SW is the source of the internal N-channel MOSFET switch
and the drain of the internal N-channel MOSFET synchronous rectifier.
Connect SW to the inductor with a wide short PCB trace and minimize its
area to reduce EMI.
9, 10, 11
SW
Bootstrap Supply for High Side Gate Driver. Connect a 0.1F capacitor
between BOOT and SW to power the internal gate driver.
12
BOOT
VIN
Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a
suitably large (10F x 2) ceramic capacitors at this pin.
13, 14
Internal Linear Regulator Supply Input. VCC supplies power for the internal
linear regulator that powers the IC. Connect VIN to the input voltage and
bypass to ground with a 0.1F ceramic capacitor.
15
16
VCC
VS
Output Voltage Sense Input Pin.
Copyright 2015 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2855A/B-01 September 2015
www.richtek.com
3
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