Boost Converter. RT9277A Datasheet

RT9277A Converter. Datasheet pdf. Equivalent

RT9277A Datasheet
Recommendation RT9277A Datasheet
Part RT9277A
Description Low Noise Boost Converter
Feature RT9277A; RT9277A/B High Performance, Low Noise Boost Converter General Description The RT9277A/B is a high .
Manufacture Richtek
Datasheet
Download RT9277A Datasheet




Richtek RT9277A
RT9277A/B
High Performance, Low Noise Boost Converter
General Description
The RT9277A/B is a high performance, low noise, fixed
frequency step up DC-DC Converter. The RT9277A/B
converters input voltage ranging 2.5V to 5.5V into output
voltage up to 16V. Current mode control with external
compensation network makes it easy to stabilize the
system and keep maximum flexibility. Soft start function
minimizes impact on the input power system. Internal power
MOSFET with very low RDS(ON) provides high efficiency.
The RT9277A/B automatically transits from PWM to PSM
(Pulse Skipping Mode) during light load condition further
increasing efficiency. 640kHz and 1.2MHz operation
frequency options provide flexibiltity of minimum output
inductor size, maximum efficiency and low BOM cost.
The RT9277A/B also provides comprehensive protection
functions such as UVLO, OCP and OTP.
Features
z 90% Efficiency
z VIN Operating Range : 2.5V to 5.5V
z 1.6A, 0.2Ω, 16V Internal Power MOSFET
z 640kHz and 1.2MHz Operation Frequency
z External Compensation Network
z Internal/External Programmable Soft Start Function
z Small MSOP8 Package
z OCP and OTP Function are Included
z RoHS Compliant and 100% Lead (Pb)-Free
Applications
z TFT LCD panel
z OLEDDisplay
z PCMCIA Cards
z Portable Device
Ordering Information
RT9277A/B
Package Type
F : MSOP-8
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Note :
Soft Start Function
A : Internal
B : External Programmable
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Pin Configurations
(TOP VIEW)
COMP
FB
EN
GND
18
27
36
45
RT9277A
COMP
FB
EN
GND
18
27
36
45
RT9277B
Marking Information
MSOP-8
For marking information, contact our sales representative
directly or through a RichTek distributor located in your
area.
NC
FREQ
VIN
LX
SS
FREQ
VIN
LX
DS9277A/B-04 April 2011
www.richtek.com
1



Richtek RT9277A
RT9277A/B
Typical Application Circuit
VIN
2.5V to 5.5V
C1
L1
Chip Enable
D1
5 LX
GND 4
6 VIN
EN 3
7 FREQ FB 2
8 NC COMP 1
C2
R3
RT9277A
C4 C3
VOUT
R1
R2
VIN
2.5V to 5.5V
C1
Figure 1
Chip Enable
L1 D1
5 LX
GND 4
6 VIN
EN 3
7 FREQ FB 2
8 SS COMP 1
C2
R3
CSS RT9277B
C4 C3
VOUT
R1
R2
Figure 2
Symbol
(unit)
Application 1
Application 2
Application 3
Table 1. Component Selection
VIN VOUT FOSC C1
(V) (V) (Hz) (uF)
L1
(uH)
C2
(uF)
R3 C3 C4
(k) (pF) (pF)
3.3 9 1.2M 10 4.7(TDK SLF6028) 33 (ceramic) 82 820 10
3.3 12 1.2M 10 4.7(TDK SLF6028) 33 (ceramic) 180 680 22
3.3 12 640K 10 10(TDK SLF6028) 33 (ceramic) 120 1200 22
Function Block Diagram
www.richtek.com
2
EN
COMP
FB
FREQ
LX
VIN Protection
VFB
Internal
Soft-Start
1.24V
Error
Amplifier
-
+
Summing
Comparator
-
+
5uA
Oscillator
Slope
Compen-
sation
Clock
Control
and
Driver
Logic
Current
Sense
RT9277A
N
VIN
LX
GND
DS9277A/B-04 April 2011



Richtek RT9277A
RT9277A/B
EN
COMP
FB
FREQ
LX
VIN Protection
VFB
1.24V
Error
Amplifier
-
+
Summing
Comparator
-
+
5uA
Oscillator
Slope
Compen-
sation
Clock
4uA
Soft-
Start
Control
and
Driver
Logic
N
Current
Sense
RT9277B
VIN
SS
LX
GND
Operation
The RT9277A/B is a high efficiency step-up Boost converter
with a fixed-frequency, current-mode PWM architecture.
It performs fast transient response and low noise operation
with appropriate component selection. The output voltage
is regulated through a feedback control consisting of an
error amplifier, a summing comparator, and several control
signal generators (as shown in function block diagram).
The feedback reference voltage is 1.24V. The error amplifier
varies the COMP voltage by sensing the FB pin. The slope
compensation signal summed with the current -sense
signal will be compared with the COMP voltage through
the summing comparator to determine the current trip point
and duty cycle. When driving light loads, the RT9277A/B
will perform the pulse-skipping mode to prevent
overcharging the output voltage. In this mode, the switching
frequency will be reduced to perform a higher efficiency.
Soft-Start
The RT9277B provides programmable soft-start function.
When the EN pin is connected to high, a 4μA constant
current is sourced to charge an external capacitor. The
voltage rate of rise on the COMP pin is limited during the
charging period, and so is the peak inductor current.
When the EN pin is connected to GND, the external
capacitor will be discharged to ground for the next time
soft-start.
Current Limitation
The switch current is monitored to limit the value not to
exceed 1.6A typically. When the switch current reaches
1.6A, the output voltage will be pulled down to limit the
total output power to protect the power switch and external
components.
Shutdown
Connect the EN to GND to turn the RT9277A/B off and
reduce the supply current to 0.1μA. In this operation, the
output voltage is the value of VIN to subtract the forward
voltage of catch diode.
Frequency Selection
The switching frequency of RT9277A/B can be selected to
operate at either 640kHz or 1.2MHz. When the FREQ pin
is connected to GND for 640kHz operation, and connected
to VIN for 1.2MHz operation. FREQ is preset to 640kHz
operation for allowing the FREQ pin unconnected.
DS9277A/B-04 April 2011
www.richtek.com
3







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