Download RT9277BGF MSOP-8 升压IC

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RT9277BGF
MSOP-8
升压 IC
广泛应用于 TFT 面板、机顶盒、智能手机等产品
Preliminary
RT9277A/B
High Performance, Low Noise Boost
Converter
General Description
The RT9277A/B is a high performance, low noise, fixedfrequency step up DC-DC Converter.
The RT9277A/Bconverters input voltage ranging 2.5V to 5.5V into outputvoltage up to
16V. Current mode control with externalcompensation network makes it easy to
stabilize thesystem and keep maximum flexibility. Soft start functionminimizes
impact on the input power system. Internal powerMOSFET with very low RDS(ON) provides
high efficiency.The RT9277A/B automatically transits from PWM to PSM(Pulse Skipping
Mode) during light load condition furtherincreasing efficiency. 640kHz and 1.2MHz
operationfrequency options provide flexibiltity of minimum outputinductor size,
maximum efficiency and low BOM cost.The RT9277A/B also provides comprehensive
protectionfunctions such as UVLO, OCP and OTP.
Features
zzzzzzzzz
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90% Efficienchttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666cey
VIN Operating Range : 2.5V to 5.5V
1.6A, 0.2Ω, 16V Internal Power MOSFET640kHz and 1.2MHz Operation FrequencyExternal
Compensation Network
Internal/External Programmable Soft Start FunctionSmall MSOP8 Package
OCP and OTP Function are Included
RoHS Compliant and 100% Lead (Pb)-Free
Applications
zzzz
TFT LCD panelOLED DisplayPCMCIA CardsPortable Device
Ordering Information
A : Internal
B : External Programmable
Pin Configurations
(TOP VIEW)
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COMP
FBENGND
2376NCFREQVINLX
RT9277A
Note :
RichTek Pb-free and Green products are :
`RoHS compliant and compatible with the current require-
ments of IPC/JEDEC
J-STD-020.
COMP
FBENGND
2376SSFREQVINLX
`Suitable for use in SnPb or Pb-free soldering processes.`100%matte tin (Sn)
plhttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceating.
RT9277BMSOP-8
Marking Information
For marking information, contact our sales representativedirectly or through a
RichTek distributor located in yourarea, otherwise visit our website for detail.
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DS9277A/B-02
March
2007
www.richtek.com
1
RT9277A/B
Typical Application Circuit
Preliminary
VVOUTFigure 1
VVOUTFigure 2
Function Block Diagram
RT9277A
www.richtek.com2
DS9277A/B-02
Preliminary
RT9277A/B
RT9277B
March
2007
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Operation
The RT9277A/B is a high efficiency step-up Boost converterwith a fixed-frequency,
current-mode PWM architecture.It performs fast transient response and low noise
operationwith appropriate component selection. The output voltageis regulated
through a feedback control consisting of anerror amplifier, a summing comparator,
ahttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666cend
several
controlsignal generators (as shown in function block diagram).The feedback reference
voltage is 1.24V. The error amplifiervaries the COMP voltage by sensing the FB pin.
The slopecompensation signal summed with the current -sensesignal will be compared
with the COMP voltage throughthe summing comparator to determine the current trip
pointand duty cycle. When driving light loads, the RT9277A/Bwill perform the
pulse-skipping mode to preventovercharging the output voltage. In this mode, the
switchingfrequency 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 constantcurrent is sourced to charge an external capacitor. Thevoltage
rate of rise on the COMP pin is limited during thecharging period, and so is the peak
inductor current.
When
the
EN
pin
is
connected
to
GND,
the
externalcapacitor
dischttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceharged
will
to
be
ground
for the next timesoft-start.
Current Limitation
The switch current is monitored to limit the value not toexceed 1.6A typically. When
the switch current reaches1.6A, the output voltage will be pulled down to limit
thetotal output power to protect
the power switch and externalcomponents.Shutdown
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Connect the EN to GND to turn the RT9277A/B off andreduce the supply current to 0.1μA.
In this operation, theoutput voltage is the value of VIN to subtract the
forwardvoltage of catch diode.Frequency Selection
The switching frequency of RT9277A/B can be selected tooperate at either 640kHz or
1.2MHz. When the FREQ pinis connected to GND for 640kHz operation, and connectedto
VIN for 1.2MHz operation. FREQ is preset to 640kHzoperation for allowing the FREQ
pin unconnected.
DS9277A/B-02
March
2007
www.richtek.com
3
RT9277A/B
Preliminary
://www.mianfeiwendang.com/doc/b57e378979599972c8a666cerwww.richtek.com
DS9277A/B-02
March
2007
4
Preliminary
Absolute Maximum Ratings
zzzz
(Note 1)
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RT9277A/B
z
zzzz
Supply
Voltage
(VIN)-------------------------------------------------------------------------------------------------?0.3
to
6VLX
to
GND--------------------------------------------------------------------------------------------------------------?0.3V
to
16VThe
other
pins---------------------------------------------------------------------------------------------------------?0.3V to 6VPower Dissipation, PD @ TA = 70°C
MSOP-8----------------------------------------------------------------------------------------------------------------625mWPackage Thermal Resistance
(Note 4)
MSOP-8,
θJA-----------------------------------------------------------------------------------------------------------160°C/WJunction
Temhttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceperature-----------------------------------------------------------------------------------------------150°CLead
Temperature
(Soldering,
10
sec.)--------------------------------------------------------------------------260°C
Storage
Temperature
Range---------------------------------------------------------------------------------------?65°C to 150°CESD Susceptibility
(Note 2)
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HBM
(Human
Body
Mode)-----------------------------------------------------------------------------------------2kVMM
(Machine
Mode)-------------------------------------------------------------------------------------------------200V
Recommended Operating Conditions
(Note 3)
zz
Junction
Temperature
Range---------------------------------------------------------------------------------------?40°C
to
125°CAmbient
Temperature
Range-----------------------------------------------------------------------------http://www.mianfeiwendang.com/doc/b57e378979599972c8a666ce----------?40°C to
85°C
Electrical Characteristics
To be continued
DS9277A/B-02
www.richtek.com
5
RT9277A/B
March
2007
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Preliminary
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 theoperational sections of the specifications is not
implied. Exposure to absolute maximum rating conditions for extendedperiods may
remain possibility to affect device reliability.
Note 2. Devices are ESD sensitive. Handling precaution recommended.
Note 3. The device is not guaranteed to function outside its operating conditions.
Note 4. θJA is measured in the natural convection at TA = 25°C on a low effective
single layer thermal conductivity test board of
://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceJEDEC
measurement standard.
www.richtek.com
6
DS9277A/B-02
March
2007
Preliminary
Typical Operating Characteristics
Efficiency vs. Output Current
51-3
thermal
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959085
RT9277A/B
Efficiency vs. Output Current
100
90
Efficiency (%)
Efficiency (%)
80757065605550
20
40
60
80
100120140160180200
80
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70
60
50
50
100
150
200
250
300
350
400
Output Current (mA)Output Current (mA)
Efficiency vs. Output Current
100
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Output Voltage vs. Output Current
12.06
90
12.04
Efficiency (%)
80
Output Voltage (V)
12.0212.0011.9811.96
70
60://www.mianfeiwendang.com/doc/b57e378979599972c8a666cear
50
50
100
150
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200
250
300
350
400
11.94
20
40
60
80
100120140160180200
Output Current (mA)Output Current (mA)
Output Voltage vs. Output Current
12.0612.04
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Output Voltage vs. Output Current
9.00
Output Voltage (V)
12.0011.9811.9611.9411.92
Output Voltage (V)
12.02
8.96
8.92
8.88
8.84
11.90
50
100
150
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200
250
300
350
8.80
50
100
150
200
250
300
350
Output Current (mA)Output Current (mA)
DS9277A/B-02
March
2007
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7
RT9277A/B
Prelimhttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceinary
Output Voltage vs. Input Voltage
11.98611.984
Output Voltage vs. Input Voltage
Output Voltage (V)
11.98211.98011.97811.97611.974
11.972
2.5
2.8
3.0
3.3
3.5
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3.8
4.0
4.3
4.5
4.8
5.0
2.5
2.8
3.0
3.3
3.5
3.8
4.0
4.3
4.5
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4.8
5.0
Input Voltage (V)Input Voltage (V)
No Load Supply Current vs. Input Voltage
500
Current Limit vs. Input Voltage
1.81.7
No Load Supply Current (uA
)
450
Current Limit (mA
)
400350300250200150
2.5
3
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3.5
4
4.5
5
5.5
1.61.51.41.3
1.22.5
3.0
3.5
4.0
http://www.mianfeiwendang.com/doc/b57e378979599972c8a666ce4.5
5.0
5.5
Input Voltage (V)Input Voltage (V)
VFB vs. Temperature
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1.2381.2381.2371.2371.2361.2361.2351.2351.2341.234
-40
-20
20
40
60
80
100
1200
Frequency vs. Temperature
1300
Frequency (kHz)
VFB Voltage(V)
1100
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1000
900
800
-40
-20
20
40
60
80
100
Temperature(°C)Temperature(°C)
www.richtek.com8
DS9277A/B-02
Preliminary
March
2007
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RT9277A/B
Power Off
Start Up
VL1(10V/Div)
VL1(10V/Div)
VOUT(5V/Div)VEN(5V/Div)ILOAD(1A/Div)
VIN = 3.3V, IOUT = 200mA, f = 640kHz
VOUT(5V/Div)VEN(5V/Div)ILOAD(1A/Div)
VIN = 3.3V, IOUT = 200mA, f = 640kHz
http://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceTime
(500μs/Div)
SwitchingSwitching
VL1(10V/Div)VOUT accoupled(100mV/Div)
VL1(10V/Div)VOUT accoupled(100mV/Div)
IL1
(500mA/Div)
(2.5ms/Div)Time
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VIN = 3.3V, IOUT = 200mA, f = 640kHz
IL1
(500mA/Div)
VIN = 3.3V, IOUT = 200mA, f = 1.2MHz
Time (1μs/Div)Time (1μs/Div)
Load Transient Response
Load Transient Response
VOUT accoupled(500mV/Div)
VOUT accoupled(500mV/Div)
ILOAD
(200mA/Div)
VIN = 3.3V, f = 640kHz
ILOAD
(100mA/Div)
VIN = 3.3V, f = 1.2MHz
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Time (250μs/Div)
Time (250μs/Div)
DS9277A/B-02
March
2007
www.richtek.com
9
RT9277A/B
Application Information
Preliminary
The design procedure of Boost converter can start fromthe maximum input current, which
is
related
about
inductohttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666cer,catch-diode
input/output capacitor selections and themaximum power which internal switch can
stand. It canbe derived from maximum output power, minimum inputvoltage and the
efficiency of Boost converter. Once themaximum input current is calculated, the
inductor valuecan 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 materialsuch as ferrite core to reduce the core loss and
chooselow ESR wire to reduce copper loss. The most importantpoint is to prevent the
core saturated when handling themaximum peak current. Using a shielded inductor
canminimize radiated noise in sensitive applications. Themaximum peak inductor
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current is the maximum inputcurrent plus the half of inductor ripple current.
Thecalculated peak current has to be smaller than the currentlimitation in the
electrical
characteristics.http://www.mianfeiwendang.com/doc/b57e378979599972c8a666ce
A
typical settingof the inductor ripple current is 20% to 40% of themaximum input
current. If the selection is 40%, themaximum peak inductor current is :
IPEAK = IIN(MAX) IRIPPLE=1.2×IIN(MAX)
2
?IOUT(MAX)×VOUT?
= 1.2×? ×VIN(MIN)??
Input Capacitor Selection
For better input bypassing, low-ESR ceramic capacitors
are recommended for performance. A 10μF input capacitoris sufficient for most
applications. For a lower output powerrequirement application, this value can be
decreased.Output Capacitor Selection
For lower output voltage ripple, low-ESR ceramic capacitorsare recommended. The
tantalum capacitors can be usedas well, but the ESR is bigger than ceramic capacitor.
Theoutput voltage ripple consists of two components: one isthe pulsating output
ripple current flows through the ESR,and the other is the capacitive ripple caused
by chargingand discharging.
://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceparVRIPPLE=VRIPPLE_ESR
VRIPPLE_C
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?VIN?I?V
?IPEAK×RESR PEAK?OUT?
COUT?VOUT×fOSC?Output Voltage
The regulated output voltage is calculated by :
VOUT=VREF×??1 ??
?R2?
Where VREF = 1.24V typical.
For most applications, R2 is a suggested a value up to100kΩ Place the
resistor-divider as close to the IC aspossible to reduce the noise sensitivity.Loop
Compensation
The RT9277A/B voltage feedback loop can be compensatedwith an external compensation
network consisted of R3,C3 and C4 (As shown in Figure 1). Choose R3 to set
thehigh-frequency integrator gain for fast transient responsewithout over or under
compensation. Once R3 isdetermined, C3 is selected to set the integrator zero
tomaintain loop stability. The purpose of C4 is to cancel thezero caused by output
capacitor and the capacitor ESR. Ifthe ceramic capacitor is selected to be the output
capacitor,Chttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ce4
can
be
taken off because of the small ESR. C2 is theoutput capacitor as shown in Figure 1.
The followingequations give approximate calculations of eachcomponent :
The minimum inductance value is derived from the followingequation :
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L =
η×VIN(MIN)×[VOUT-VIN(MIN)]
2
0.4×IOUT(MAX)×VOUT×fOSC
2
Depending on the application, the recommended inductorvalue is between 2.2μH to
10μH.Diode Selection
To achieve high efficiency, Schottky diode is good choicefor low forward drop voltage
and fast switching time. Theoutput diode rating should be able to handle the
maximumoutput voltage, average power dissipation and the pulsatingdiode peak
current.
www.richtek.com10
DS9277A/B-02
March
Preliminary
200×VOUT2×C2R3 =
L1
-3
2007
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C3 =VIN
0.005×RESR×L1C4 =VOUT2
RT9277A/B
The best criterihttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceon to
optimize the loop compensation isby inspecting the transient response and adjusting
thecompensation network.Soft-Start Capacitor
The soft-start function begins from VSS = 0V to VSS = 1.24Vwith a 4μA constant current
charging to the soft-startcapacitor, so the capacitor should be large enough to letthe
output voltage reach regulation inside the soft-startcycle. Typical value of
soft-start capacitor range is from10nF to 200nF. After the cycle finished, the load
can startto draw maximum current as required.Layout Guideline
For high frequency switching power supplies, the PCBlayout is important step in system
application design. Inorder to let IC achieve good regulation, high efficiency
andstability, it is strongly recommended the powercomponents should be placed as
close as possible. Thesetraces should be wide and short. The feedback pin and
thenetworks
of
feedback
and
compensation
should
keep
phttp://www.mianfeiwendang.com/doc/b57e378979599972c8a666ceower
shielded with a ground traceor plane to prevent noise coupling.
DS9277A/B-02
www.richtek.com
11
March
2007
awayfrom
loops,
and
the
be
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RT9277A/B
Outline Dimension
Preliminary
L
A2
8-Lead MSOP Plastic Package
Richtek Technology Corporation
Headquarter
5F, No. 20, Taiyuen Street, Chupei CityHsinchu, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing)
8F, No. 137, Lane 235, Paochiao Road, Hsintien CityTaipei County, Taiwan, R.O.C.
Tel: (8862)89191466 Fax: (8862)89191465Email: [email protected]
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DS9277A/B-02
March
2007
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