RT8289
Functional Pin Description
Pin No.
1
2, 3
4
Pin Name
BOOT
NC
FB
Pin Function
High Side Gate Drive Bootstrap Input. BOOT supplies the drive for the high side
N-MOSFET switch. Connect a 10nF or greater capacitor from SW to BOOT to
power the high side switch.
No Internal Connection.
Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB
with a resistive voltage divider from the output voltage. The value of the divider
resistors also sets loop bandwidth. The feedback threshold is 1.222V.
Chip Enable (Active High). EN is a digital input that turns the regulator on or off.
Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off.
For automatic startup, leave EN unconnected.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Power Input. VIN supplies the power to the IC, as well as the step-down
converter switches. Drive V
IN
with a 5.5V to 32V power source. Bypass V
IN
to
GND with a suitably large capacitor to eliminate noise on the input to the IC.
Power Switching Output. SW is the switching node that supplies power to the
output. Connect the output LC filter from SW to the output load. Note that a
capacitor is required from SW to BOOT to power the high side switch.
5
EN
6,
GND
9 (Exposed Pad)
7
VIN
8
SW
Function Block Diagram
VIN
Ramp
Generator
Current Sense
Amplifier
-
+
BOOT
EN
Regulator
Oscillator
500kHz
+
-
S
Q
R
SW
Bootstrap
Control
GND
Driver
Reference
FB
12k
Error
Amplifier
+
-
PWM
Comparator
OC Limit
Clamp
400k
30pF
13pF
www.richtek.com
2
DS8289-01 March 2011
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
