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 R
DS(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
90% Efficiency
V
IN
Operating Range : 2.5V to 5.5V
1.6A, 0.2Ω, 16V Internal Power MOSFET
Ω
640kHz and 1.2MHz Operation Frequency
External Compensation Network
Internal/External Programmable Soft Start Function
Small MSOP8 Package
OCP and OTP Function are Included
RoHS Compliant and 100% Lead (Pb)-Free
Applications
TFT LCD panel
OLED Display
PCMCIA Cards
Portable Device
Ordering Information
RT9277A/B
Package Type
F : MSOP-8
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Soft Start Function
A : Internal
B : External Programmable
Note :
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
1
2
3
4
8
7
6
5
NC
FREQ
VIN
LX
RT9277A
COMP
FB
EN
GND
1
2
3
4
8
7
6
5
SS
FREQ
VIN
LX
RT9277B
MSOP-8
Marking Information
For marking information, contact our sales representative
directly or through a RichTek distributor located in your
area.
DS9277A/B-04 April 2011
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1
RT9277A/B
Typical Application Circuit
Chip Enable
V
IN
2.5V to 5.5V
C1
L1
+
5 LX
6 VIN
GND 4
EN 3
R3
C4
RT9277A
C3
R2
7 FREQ
FB 2
8 NC
COMP 1
D1
V
OUT
C2
R1
+
Figure 1
Chip Enable
V
IN
2.5V to 5.5V
C1
L1
+
5 LX
6 VIN
GND 4
EN 3
R3
C4
RT9277B
C3
R2
7 FREQ
FB 2
8 SS
COMP 1
C
SS
D1
V
OUT
C2
R1
+
Figure 2
Table 1. Component Selection
F
OSC
C1
L1
C2
(Hz)
(uF)
(uH)
(uF)
1.2M
10
4.7(TDK SLF6028)
33 (ceramic)
Symbol
(unit)
Application 1
Application 2
Application 3
V
IN
(V)
3.3
3.3
3.3
V
OUT
(V)
9
12
12
R3
(kΩ)
82
180
120
C3
(pF)
820
680
1200
C4
(pF)
10
22
22
1.2M
640K
10
10
4.7(TDK SLF6028)
10(TDK SLF6028)
33 (ceramic)
33 (ceramic)
Function Block Diagram
LX
V
IN
V
FB
Error
Amplifier
-
+
Protection
Internal
Soft-Start
EN
COMP
VIN
FB
1.24V
Summing
Comparator
-
+
Clock
Control
and
Driver
Logic
LX
N
GND
5uA
FREQ
Oscillator
Slope
Compen-
sation
Current
Sense
RT9277A
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2
DS9277A/B-04 April 2011
RT9277A/B
LX
V
IN
V
FB
Error
Amplifier
-
+
4uA
Protection
Soft-
Start
Summing
Comparator
-
+
Clock
5uA
FREQ
Oscillator
Slope
Compen-
sation
Current
Sense
SS
LX
N
GND
VIN
EN
COMP
FB
1.24V
Control
and
Driver
Logic
RT9277B
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 V
IN
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
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3
RT9277A/B
Functional Pin Description
Pin No.
RT9277A
1
2
3
4
5
6
7
RT9277B
1
2
3
4
5
6
7
Pin Name
Pin Function
Compensation Pin for Error Amplifier. Connect a compensation network
to ground. See the Component Selection Table for the loop
compensation.
Feedback Pin. Connect an external resistor-divider tap to FB. The typical
reference voltage is 1.24V.
Shutdown Control Input. Connect EN to GND to turn off the RT9277A/B.
Ground
Switch Pin. Connect the inductor and catch diode to LX pin. Widen and
shorten the connected trace to minimize EMI.
Supply Pin. Place at least a 1μF ceramic capacitor close to RT9277A/B
for bypassing noise.
Frequency Select Pin. Oscillator frequency is 640kHz as FREQ
connected to GND, and 1.2MHz as FREQ connected to VIN. A 5μA
pull-down current is sinking on this pin.
Soft-Start Control Pin. Connect a soft-start capacitor (C
SS
) to this pin. A
4μA constant current charges the soft-start capacitor. When EN
connected to GND, the soft-start capacitor is discharged. When EN
connected to VIN high, the soft-start capacitor is charged to VIN. Leave
floating for not using soft-start.
No Connection
COMP
FB
EN
GND
LX
VIN
FREQ
--
8
SS
8
--
NC
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DS9277A/B-04 April 2011
RT9277A/B
Absolute Maximum Ratings
(Note 1)
−0.3
to 6V
−
0.3V to 16V
−
0.3V to 6V
625mW
160°C/W
Supply Voltage (V
IN
) ------------------------------------------------------------------------------------------------
LX to GND -------------------------------------------------------------------------------------------------------------
The other pins --------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 70°C
MSOP-8 ---------------------------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
MSOP-8,
θ
JA
----------------------------------------------------------------------------------------------------------
Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------------
−
65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V
Recommended Operating Conditions
(Note 4)
Junction Temperature Range --------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 3V,
FREQ left
floating, T
A
= 25°C, Unless Otherwise specification)
Parameter
System Supply Input
Operation Voltage Range
Under Voltage Lock Out
Power On Reset Hysteresis
Quiescent Current
Shut Down Current
Soft start Current (RT9277B)
Switching Regulator Oscillator
Free Run Frequency
Maximum Duty Cycle
Reference Voltage
Feedback Reference Voltage
Error Amplifier
Transconductance
Voltage Gain
G
m
A
V
70
--
140
700
240
--
uΩ
V/V
V
REF
V
C OMP
= 1.24V
1.222
1.24
1.258
V
FREQ = GND
f
OSC
FREQ = V
IN
540
--
82
640
1200
90
740
--
96
%
kHz
I
Q
I
SHDN
I
SS
V
FB
= 1.3V, No switching
V
FB
= 1.0V, Switching, No load
EN = GND
V
SS
= 1.2V
V
IN
UVLO
2.5
1.9
--
--
--
--
1.5
--
2
100
250
2
--
4
5.5
2.1
--
350
5
1
7
V
V
mV
uA
mA
uA
uA
Symbol
Test Conditions
Min
Typ
Max
Unit
To be continued
DS9277A/B-04 April 2011
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5
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