RT8055B
Typical Application Circuit
V
IN
5V
6
C
IN
22µF
R4
100k
C1
PGOOD
R
OSC
180k
8
1
PGOOD
SHDN/RT
GND
PGND
R3
7
VDD
FB 9
COMP
10
R
COMP
30k
C
COMP
470pF
RT8055B
3, 4
PVDD
LX
L1
2µH
C
F
22pF
R1
75k
R2
24k
V
OUT1
3.3V/3A
C
OUT
22µF x 2
2,11 (Exposed Pad)
5
Note : Using X5R/X7R Ceramic Capacitors
Table 1. Recommended Component Selsction
V
OUT
3.3
2.5
1.8
1.5
1.2
1.0
R1 (kΩ)
75
51
30
21
12
6
R2 (kΩ)
24
24
24
24
24
24
R
COMP
(kΩ)
30
27
22
18
15
13
C
COMP
(nF)
0.47
0.47
0.47
0.47
0.47
0.47
L1 (μH)
2.2
2.2
2.2
2.2
1.0
1.0
C
OUT
(μF)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
Functional Pin Description
Pin No.
1
Pin Name
Pin Function
Shutdown Control or Frequency Setting Input. Connect a resistor to ground from
device to be shut down.
Signal Ground. All small-signal components and compensation components should
2,
11 (Exposed Pad)
3, 4
5
6
7
8
9
GND
be connected to this ground, which in turn connects to PGND at one point. The
exposed pad must be soldered to a large PCB and connected to GND for maximum
power dissipation.
LX
PGND
PVDD
VDD
PGOOD
FB
Internal Power MOSFET Switches Output. Connect this pin to the inductor.
Power Ground. Connect this pin close to the negative terminal of C
IN
and C
OUT
.
Power Supply Input. Decouple this pin to PGND with a capacitor.
Signal Supply Input. Decouple this pin to GND with a capacitor. Generally, V
DD
is
equal to PVDD.
Power Good Indicator. The pin is an open drain logic output that is pulled to Ground.
Feedback Pin. This pin receives the feedback voltage from a resistive divider
connected across the output.
Error Amplifier Compensation Point. The current comparator threshold increases
10
COMP
with this control voltage. Connect external compensation elements to this pin to
stabilize the control loop.
SHDN/RT this pin sets the switching frequency. Force this pin to V
DD
or GND causes the
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DS8055B-03 April 2011
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
