DS9277AB 04

RT9277A/B
High Performance, Low Noise Boost Converter
General Description
Features
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.
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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.
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The RT9277A/B also provides comprehensive protection
functions such as UVLO, OCP and OTP.
Ordering Information
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90% Efficiency
VIN Operating Range : 2.5V to 5.5V
Ω, 16V Internal Power MOSFET
1.6A, 0.2Ω
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
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TFT LCD panel
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OLED Display
PCMCIA Cards
Portable Device
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Pin Configurations
RT9277A/B
Package Type
F : MSOP-8
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
(TOP VIEW)
COMP
FB
EN
GND
Soft Start Function
A : Internal
B : External Programmable
Note :
Richtek products are :
`
RoHS compliant and compatible with the current require-
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
ments of IPC/JEDEC J-STD-020.
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Suitable for use in SnPb or Pb-free soldering processes.
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
L1
D1
VOUT
+
+
VIN
2.5V to 5.5V
C2
C1
5 LX
6 VIN
GND 4
EN 3
7 FREQ
FB 2
8 NC
COMP 1
R1
R3
C4
RT9277A
R2
C3
Figure 1
Chip Enable
D1
L1
VOUT
+
+
VIN
2.5V to 5.5V
C2
C1
5 LX
6 VIN
GND 4
EN 3
7 FREQ
FB 2
8 SS
COMP 1
R1
R3
C4
CSS
RT9277B
R2
C3
Figure 2
Table 1. Component Selection
FOSC
C1
L1
C2
(Hz)
(uF)
(uH)
(uF)
1.2M
10
4.7(TDK SLF6028)
33 (ceramic)
R3
(kΩ)
82
C3
(pF)
820
C4
(pF)
10
Symbol
(unit)
Application 1
VIN
(V)
3.3
VOUT
(V)
9
Application 2
3.3
12
1.2M
10
4.7(TDK SLF6028)
33 (ceramic)
180
680
22
Application 3
3.3
12
640K
10
10(TDK SLF6028)
33 (ceramic)
120
1200
22
Function Block Diagram
LX
VIN
VFB
EN
COMP
FB
1.24V
Error
Amplifier
+
Protection
Summing
Comparator
+
Internal
Soft-Start
Control
and
Driver
Logic
Clock
VIN
LX
N
GND
5uA
FREQ
Oscillator
Slope
Compensation
Current
Sense
RT9277A
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DS9277A/B-04 April 2011
RT9277A/B
LX
VIN
VFB
EN
COMP
FB
1.24V
4uA
VIN
Protection
SoftStart
Error
Amplifier
+
Summing
Comparator
+
Control
and
Driver
Logic
SS
LX
N
Clock
GND
5uA
FREQ
Oscillator
Slope
Compensation
Current
Sense
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.
When the EN pin is connected to GND, the external
capacitor will be discharged to ground for the next time
soft-start.
Soft-Start
Frequency Selection
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.
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
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.
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RT9277A/B
Functional Pin Description
Pin No.
Pin Name
Pin Function
RT9277A
RT9277B
1
1
COMP
2
2
FB
3
3
EN
Shutdown Control Input. Connect EN to GND to turn off the RT9277A/B.
4
4
GND
Ground
5
5
LX
6
6
VIN
7
7
FREQ
--
8
SS
8
--
NC
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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.
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 (CSS) 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
DS9277A/B-04 April 2011
RT9277A/B
Absolute Maximum Ratings
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(Note 1)
Supply Voltage (VIN) ------------------------------------------------------------------------------------------------ −0.3 to 6V
LX to GND ------------------------------------------------------------------------------------------------------------- − 0.3V to 16V
The other pins -------------------------------------------------------------------------------------------------------- − 0.3V to 6V
Power Dissipation, PD @ TA = 70°C
MSOP-8 --------------------------------------------------------------------------------------------------------------- 625mW
Package Thermal Resistance (Note 2)
MSOP-8, θJA ---------------------------------------------------------------------------------------------------------- 160°C/W
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
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(Note 4)
Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3V, FREQ left floating, TA = 25°C, Unless Otherwise specification)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
System Supply Input
Operation Voltage Range
V IN
2.5
--
5.5
V
Under Voltage Lock Out
UVLO
1.9
2
2.1
V
--
100
--
mV
VFB = 1.3V, No switching
--
250
350
uA
VFB = 1.0V, Switching, No load
--
2
5
mA
Power On Reset Hysteresis
Quiescent Current
IQ
Shut Down Current
ISHDN
EN = GND
--
--
1
uA
Soft start Current (RT9277B)
ISS
VSS = 1.2V
1.5
4
7
uA
FREQ = GND
540
640
740
--
1200
--
82
90
96
%
1.222
1.24
1.258
V
Switching Regulator Oscillator
Free Run Frequency
fOSC
FREQ = VIN
Maximum Duty Cycle
kHz
Reference Voltage
Feedback Reference Voltage
V REF
VC OMP = 1.24V
Error Amplifier
Transconductance
Gm
70
140
240
uΩ
Voltage Gain
AV
--
700
--
V/V
To be continued
DS9277A/B-04 April 2011
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RT9277A/B
Parameter
Symbol
Test Conditions
Feedback Voltage Line
VCOMP = 1.24V,
Regulation
2.5V < VIN < 5.5V
Min
Typ
Max
Unit
--
0.05
0.15
%/V
--
200
500
mΩ
1.2
1.6
--
A
MOSFET
On Resistance of MOSFET
RDS(ON)
Current Limitation
Enable Control Input
Input Low Voltage
VIL
2.5V < VIN < 5.5V
--
--
0.3 x VIN
V
Input High Voltage
VIH
2.5V < VIN < 5.5V
0.7 x VIN
--
--
V
--
0.1
--
V
Over Temperature Protection
--
170
--
°C
Hysteresis
--
20
--
°C
Hysteresis
Protection Function
Note 1.Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of
JEDEC 51-3 thermal measurement standard.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
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DS9277A/B-04 April 2011
RT9277A/B
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
95
100
640kHz
90
640kHz
1.2MHz
85
90
Efficiency (%)
Efficiency (%)
1.2MHz
80
75
70
65
60
80
70
60
55
VIN = 3.3V, VOUT = 12V
VIN = 5.0V, VOUT = 12V
50
50
0
20
40
60
80
100 120 140 160 180 200
0
50
100
Output Current (mA)
150
200
250
300
350
400
Output Current (mA)
Efficiency vs. Output Current
Output Voltage vs. Output Current
100
12.06
VIN = 5V
12.04
VIN = 3.5V
80
70
Output Voltage (V)
Efficiency (%)
90
60
12.02
640kHz
12.00
1.2MHz
11.98
11.96
VOUT = 9.0V, f = 1.2MHz
VIN = 3.3V, VOUT = 12V
50
11.94
0
50
100
150
200
250
300
350
400
0
20
Output Current (mA)
40
60
80
100 120 140 160 180 200
Output Current (mA)
Output Voltage vs. Output Current
Output Voltage vs. Output Current
9.00
12.06
12.04
12.00
1.2MHz
11.98
640kHz
11.96
11.94
Output Voltage (V)
Output Voltage (V)
8.96
12.02
VIN = 3.5V
8.92
VIN = 5V
8.88
8.84
11.92
VOUT = 9.0V, f = 1.2MHz
VIN = 5.0V, VOUT = 12V
8.80
11.90
0
50
100
150
200
250
Output Current (mA)
DS9277A/B-04 April 2011
300
350
0
50
100
150
200
250
300
350
Output Current (mA)
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RT9277A/B
Output Voltage vs. Input Voltage
11.986
Output Voltage vs. Input Voltage
11.998
640kHz
11.996
Output Voltage (V)
Output Voltage (V)
11.984
1.2MHz
11.982
11.980
11.978
11.976
11.974
11.994
11.992
11.990
11.988
11.986
VOUT = 12V, IOUT = 1mA
VOUT = 12V, IOUT = 1mA
11.972
11.984
2.5
2.8
3.0
3.3
3.5
3.8
4.0
4.3
4.5
4.8
5.0
2.5
2.8
3.0
3.3
Input Voltage (V)
3.8
4.0
4.3
4.5
4.8
5.0
Current Limit vs. Input Voltage
No Load Supply Current vs. Input Voltage
500
1.8
640kHz
450
640kHz
1.7
Current Limit (mA)
No Load Supply Current (uA)
3.5
Input Voltage (V)
400
350
300
250
1.6
1.5
1.4
1.3
200
VOUT = 12V
VOUT = 12V
150
1.2
2.5
3
3.5
4
4.5
5
5.5
2.5
3.0
3.5
Input Voltage (V)
4.0
4.5
5.0
5.5
Input Voltage (V)
VFB vs. Temperature
Frequency vs. Temperature
1300
1.238
1.2MHz
1.2MHz
1.238
1200
Frequency (kHz)
V FB Voltage(V)
1.237
1.237
1.236
1.236
1.235
1.235
1.234
1100
1000
900
VIN = 3.3V, VOUT = 12V
VIN = 3.3V, VOUT = 12V
1.234
800
-40
-20
0
20
40
Temperature (°C)
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60
80
100
-40
-20
0
20
40
60
80
100
Temperature (°C)
DS9277A/B-04 April 2011
RT9277A/B
Start Up
Power Off
VL1
(10V/Div)
VL1
(10V/Div)
VOUT
(5V/Div)
VOUT
(5V/Div)
VEN
(5V/Div)
VEN
(5V/Div)
ILOAD
(1A/Div)
VIN = 3.3V, IOUT = 200mA, f = 640kHz
ILOAD
(1A/Div)
VIN = 3.3V, IOUT = 200mA, f = 640kHz
Time (2.5ms/Div)
Time (500μs/Div)
Switching
Switching
VL1
(10V/Div)
VL1
(10V/Div)
VOUT ac
coupled
(100mV/Div)
VOUT ac
coupled
(100mV/Div)
IL1
(500mA/Div)
IL1
(500mA/Div)
VIN = 3.3V, IOUT = 200mA, f = 640kHz
VIN = 3.3V, IOUT = 200mA, f = 1.2MHz
Time (1μs/Div)
Time (1μs/Div)
Load Transient Response
Load Transient Response
VOUT ac
coupled
(500mV/Div)
VOUT ac
coupled
(500mV/Div)
ILOAD
(100mA/Div)
ILOAD
(200mA/Div)
VIN = 3.3V, f = 640kHz
Time (250μs/Div)
DS9277A/B-04 April 2011
VIN = 3.3V, f = 1.2MHz
Time (250μs/Div)
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RT9277A/B
Application Information
The design procedure of Boost converter can start from
the maximum input current, which is related about inductor,
catch-diode input/output capacitor selections and the
maximum power which internal switch can stand. It can
be derived from maximum output power, minimum input
voltage and the efficiency of Boost converter. Once the
maximum input current is calculated, the inductor value
can be determined and the other components as well.
Inductor Selection
For a better efficiency in high switching frequency converter,
the inductor selection has to use a proper core material
such as ferrite core to reduce the core loss and choose
low ESR wire to reduce copper loss. The most important
point is to prevent the core saturated when handling the
maximum peak current. Using a shielded inductor can
minimize radiated noise in sensitive applications. The
maximum peak inductor current is the maximum input
current plus the half of inductor ripple current. The
calculated peak current has to be smaller than the current
limitation in the electrical characteristics. A typical setting
of the inductor ripple current is 20% to 40% of the
maximum input current. If the selection is 40%, the
maximum peak inductor current is :
IPEAK = IIN(MAX) + 1 IRIPPLE = 1.2 × IIN(MAX)
2
⎡ IOUT(MAX) × VOUT ⎤
= 1.2 × ⎢
⎥
⎣ η × VIN(MIN)
⎦
Input Capacitor Selection
For better input bypassing, low-ESR ceramic capacitors
are recommended for performance. A 10μF input capacitor
is sufficient for most applications. For a lower output power
requirement application, this value can be decreased.
Output Capacitor Selection
For lower output voltage ripple, low-ESR ceramic capacitors
are recommended. The tantalum capacitors can be used
as well, but the ESR is bigger than ceramic capacitor. The
output voltage ripple consists of two components: one is
the pulsating output ripple current flows through the ESR,
and the other is the capacitive ripple caused by charging
and discharging.
VRIPPLE = VRIPPLE_ESR + VRIPPLE_C
≅ IPEAK × RESR +
IPEAK ⎛ VOUT − VIN ⎞
⎜
⎟
COUT ⎝ VOUT × fOSC ⎠
Output Voltage
The regulated output voltage is calculated by :
VOUT = VREF × ⎛⎜1 + R1 ⎞⎟
⎝ R2 ⎠
Where VREF = 1.24V typical.
For most applications, R2 is a suggested a value up to
100kΩ Place the resistor-divider as close to the IC as
possible to reduce the noise sensitivity.
Loop Compensation
The minimum inductance value is derived from the following
equation :
η × VIN(MIN) × [VOUT -VIN(MIN) ]
2
L=
0.4 × IOUT(MAX) × VOUT × fOSC
2
Depending on the application, the recommended inductor
value is between 2.2μH to 10μH.
Diode Selection
To achieve high efficiency, Schottky diode is good choice
for low forward drop voltage and fast switching time. The
output diode rating should be able to handle the maximum
output voltage, average power dissipation and the pulsating
diode peak current.
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10
The RT9277A/B voltage feedback loop can be compensated
with an external compensation network consisted of R3,
C3 and C4 (As shown in Figure 1). Choose R3 to set the
high-frequency integrator gain for fast transient response
without over or under compensation. Once R3 is
determined, C3 is selected to set the integrator zero to
maintain loop stability. The purpose of C4 is to cancel the
zero caused by output capacitor and the capacitor ESR. If
the ceramic capacitor is selected to be the output capacitor,
C4 can be taken off because of the small ESR. C2 is the
output capacitor as shown in Figure 1. The following
equations give approximate calculations of each
component :
DS9277A/B-04 April 2011
RT9277A/B
R3 =
200 × VOUT 2 × C2
L1
-3
C3 = 0.4 × 10 × L1
VIN
0.005 × RESR × L1
C4 =
VOUT 2
The best criterion to optimize the loop compensation is
by inspecting the transient response and adjusting the
compensation network.
Soft-Start Capacitor
The soft-start function begins from VSS = 0V to VSS = 1.24V
with a 4μA constant current charging to the soft-start
capacitor, so the capacitor should be large enough to let
the output voltage reach regulation inside the soft-start
cycle. Typical value of soft-start capacitor range is from
10nF to 200nF. After the cycle finished, the load can start
to draw maximum current as required.
Layout Guideline
For high frequency switching power supplies, the PCB
layout is important step in system application design. In
order to let IC achieve good regulation, high efficiency and
stability, it is strongly recommended the power
components should be placed as close as possible. These
traces should be wide and short. The feedback pin and the
networks of feedback and compensation should keep away
from the power loops, and be shielded with a ground trace
or plane to prevent noise coupling.
DS9277A/B-04 April 2011
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11
RT9277A/B
Outline Dimension
D
L
E1
E
e
A2
A
A1
b
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.810
1.100
0.032
0.043
A1
0.000
0.150
0.000
0.006
A2
0.750
0.950
0.030
0.037
b
0.220
0.380
0.009
0.015
D
2.900
3.100
0.114
0.122
e
0.650
0.026
E
4.800
5.000
0.189
0.197
E1
2.900
3.100
0.114
0.122
L
0.400
0.800
0.016
0.031
8-Lead MSOP Plastic Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: marketing@richtek.com
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design,
specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed
by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
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DS9277A/B-04 April 2011