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Preliminary
RT9278
High Efficiency Boost LDO Converter & High Power White LED Driver
General Description
The RT9278 is a compact, high efficiency, synchronous step-up converter, it provides a power supply solution for products powered by either two-cell, three-cell Alkaline/ NiMH or one-cell Li-Ion/Li-polymer battery. The RT9278 is boost converter with PWM control loop, provide up to 95% efficiency by using a synchronous rectifier. The maximum peak current in the internal switch is limited to up to 2A. It keeps the output voltage regulated when the input voltage exceeds the setting output voltage. The output voltage can be set by an external resister divider, or be fixed to reduce external components. It integrates a linear controller for linear regulator. RT9278 is available in VDFN-10L 3x3 package.
Features
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95% Efficiency Synchronous Boost Converter High Supply Capability 2A Current Limit Input Voltage Range : 1.5V to 5.5V 600kHz Fixed Switching Rate Adjustable Output Voltage Options Up to 5.5V Output Voltage Keep Regulated when Input Voltage Exceed Setting Output Voltage 1A Supply Current in Shutdown Mode External Compensation Network Build in Linear Controller for Linear Regulator Over Temperature Protection Small 10-Lead VDFN Package RoHS Compliant and 100% Lead (Pb)-Free
Applications Ordering Information
RT9278 Package Type QV : VDFN-10L 3x3 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
Note : Richtek Pb-free and Green products are : }RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. }Suitable for use in SnPb or Pb-free soldering processes. }100% matte tin (Sn) plating.
FB COMP GND EN LX
1 2 3 4 5 11 10 9
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Digital Still Camera Camera White LED Flash Light PDAs Portable Device
Pin Configurations
(TOP VIEW)
LFB LDRI PGND VDD VOUT
GND
8 7 9
VDFN-10L 3x3
Marking Information
For marking information, contact our sales representative directly or through a Richtek distributor located in your area, otherwise visit our website for detail.
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RT9278
Typical Application Circuit
Chip Enable L1 1 to 10uH VIN C1 4.7uF R1 2.2k C2 12nF Chip Shutdown 100ms 4 EN 5 LX 8
Preliminary
VDD 7 RT9278 VOUT 6
C3 1uF
Q1 AO7401 C4 2.2uF
700mA 100ms D1 Power LED
PGND FB 1 LDRI 9 LFB 10
2 COMP 3 GND
R2 300k
R3 0.28
Figure 1. Novel Up-Down Driver for Power LED with Strobe Mode
Note : Patent Pending.
Chip Enable 4 L1 1 to 10uH Chip Shutdown VIN C1 4.7uF R1 2.2k C2 12nF
EN
5 LX 8
VDD 7 RT9278 VOUT 6
C3 1uF
Istrobe Q1 AO3403 C4 2.2uF IMovie GPIO R2 300k
700mA 200mA 2.8V
100ms
PGND 1 FB LDRI 9 LFB 10
2 COMP 3 GND
0V D1 Power LED
R4 1k R5 18.2k GPIO
R3 0.28
R4 = 1k 0.2 R3 = IStrobe (GPIO_HI - 0.2) x R4 R5 = 0.2 - (IMovie x R3)
Figure 2. Novel Up-Down Driver for Power LED with Strobe Mode and Movie Mode
Note :
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Patent Pending. The GPIO Signal has to pull high before enable IC.
Chip Enable L1 4.7uH VIN C1 10uF R1 2.5k Chip Shutdown VDD 7 EN RT9278 5 LX 6 2 COMP VOUT 8 PGND 9 10 LDRI LFB 1 3 FB GND 4 C3 1uF C4 10uF
Q1 AO3403 R2 510k C5 100pF R3 470k
VOUT 3.3V
C2 2.2nF
R4 150k
Figure 3. Synchronous Boost Converter with Load Disconnect in Shutdown
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Preliminary
RT9278
VIN 1.6V to 5V
L1 4.7uH C1 10uF
GPIO
4 EN 5 LX 8
VDD 7 RT9278 VOUT 6
C3 1uF C4 10pF
Q1 AO3403 R2 732k R3 226k C5 20uF R5 620k C6 22pF C7 1uF
PGND FB 1
VOUT 3.3V
R1 51k C2 3.3nF
2 COMP 3 GND
R4 510k
LDRI 9 10 LFB
R6 40.2k
Figure 4. Boost-LDO Application for Constant Output Voltage
VIN 1.6V to 3.0V
L1 4.7uH C1 20uF
GPIO
4 EN 5 LX 8
VDD 7 RT9278 VOUT 6
C3 1uF C4 10pF
VOUT1 3.3V/300mA Q1 AO3403 R2 470k R3 150k C5 40uF R5 887k C6 22pF C7 30uF
VOUT2 1.8V/150mA
PGND FB 1
R1 3.9k C2 1.5nF
2 COMP 3 GND
R4 510k
LDRI 9 10 LFB
R6 110k
Figure 5. Synchronous Boost Converter Driver for Dual Output Voltage
Chip Enable Chip Shutdown 4 EN VDD 7 RT9278 PVD CFF R2 C OUT 40uF C3 1uF VOUT
L VIN C1 10uF
5 LX 9 LDRI 10 LFB RCOMP
CCOMP
2 COMP 1 FB 3 GND PGND 8
R1
Figure 6. Synchronous Boost Converter
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RT9278
Input Voltage Output Voltage (V) (V) 1.5~3.0 1.5~3.3 3.0~4.5 3.3 5.0 5.0 L (H) 2.2 2.2 2.2
Preliminary
Table 1. Component Selection for Figure 6 (L=2.2H)
COUT (F) 40 40 40 R1 (k) 150 130 130 R2 (k) 470 680 680 RCOMP (k) 43 24 24 CCOMP (nF) 5.6 8.2 3.9 C FF (pF) 18 12 12
Table 2. Component Selection for Figure 6 (L=4.7H)
Input Voltage Output Voltage (V) (V) 1.5~3.0 1.5~3.3 3.0~4.5 3.3 5.0 5.0 L (H) 4.7 4.7 4.7 COUT (F) 40 40 40 R1 (k) 150 130 130 R2 (k) 470 680 680 RCOMP (k) 24 24 24 CCOMP (nF) 10 15 8.2 C FF (pF) 18 12 12
Table 3. Component Selection for Figure 6 (L=6.8H)
Input Voltage Output Voltage (V) (V) 1.5~3.0 1.5~3.3 3.0~4.5 3.3 5.0 5.0 L (H) 6.8 6.8 6.8 COUT (F) 40 40 40 R1 (k) 150 130 130 R2 (k) 470 680 680 RCOMP (k) 24 24 24 CCOMP (nF) 15 22 12 CFF (pF) 18 12 12
Table 4. Component Selection for Figure 6 (L=10H)
Input Voltage Output Voltage (V) (V) 1.5~3.0 1.5~3.3 3.0~4.5 3.3 5.0 5.0 L (H) 10 10 10 COUT (F) 40 40 40 R1 (k) 150 130 130 R2 (k) 470 680 680 RCOMP (k) 24 24 24 CCOMP (nF) 22 33 18 C FF (pF) 18 12 12
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Preliminary Functional Pin Description
Pin No. 1 2 3 4 5 6 7 8 9 10 Pin Name FB COMP GND EN LX VOUT VDD PGND LDRI LFB Feedback Input Pin. Feedback Compensation Pin. Ground. Enable Input Pin Switch Node. Output Pin Device Input Power Pin. Power Ground. Linear Controller Driver Output. Linear Controller Feedback Input. Pin Function
RT9278
Exposed Pad (11) GND
The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation.
Function Block Diagram
COMP Error AMPLIFIER VREF = 0.8V VDD GND Oscillator and Shutdown Control Slope Compensation Current Sense + Error Comparator +
VOUT
FB
Control and Driver Logic
LX
EN
PGND LDRI
LFB VREF = 0.2V
+
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RT9278
Operation
Preliminary
RT9278 integrates a high-efficiency step-up DC-DC converter and a linear regulator controller. The boost converter is based on a fixed frequency, pulse-width-modulation (PWM) controller using a synchronous rectifier to obtain maximum efficiency. Current mode control with external compensation network makes it easy to stabilize the system and keep maximum flexibility. The linear regulator controller can use to drive the external P-Channel MOSFET switch for load disconnection. It keeps the output voltage regulated even when the input voltage exceeds the nominal output voltage, and keeps the output voltage completely disconnected from input voltage (battery) when the chip is in shutdown mode Soft-start When the chip is enabled. Soft-start is achieved by ramping up the PWM duty from very small to normal operation. The ramping up PWM duty is achieved by sourcing 1uA from error amplifier to the compensation capacitor. When the output voltage is regulated, the PWM duty enters the normal operation, and the error amplifier can sink and source up to 22uA. The soft-start time is set by the following formula : TSS = (1V - 1A x RCOMP ) x CCOMP 1A
RCOMP and CCOMP are compensation components. Current limit The current of NMOS is sensed cycle by cycle to prevent over current. When over current limit, then the NMOS is off. This state is latched and then reset automatically at next clock cycle. Over voltage When the chip voltage is higher than 6.5V, Switch is off. When the Over Voltage Protection is relieved, the chip operates well again. Thermal protection Thermal protection function is integrated in the chip. When the chip temperature is higher than 180C, the controllers are shutdown. 20C is the hysteresis range of temperature to prevent unstable operation when the thermal protection happens. When the thermal protection is relieved, the chip operates well again.
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Preliminary Absolute Maximum Ratings
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RT9278
(Note 1)
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Supply Voltage, VDD ------------------------------------------------------------------------------------------------- 7V LX Pin Voltage -------------------------------------------------------------------------------------------------------- - 0.3V to 7V The Other pins -------------------------------------------------------------------------------------------------------- - 0.3V to 7V Power Dissipation, PD @ TA = 25C VDFN-10L 3x3 -------------------------------------------------------------------------------------------------------- 1.43W Package Thermal Resistance (Note 4) VDFN-10L 3x3, JA --------------------------------------------------------------------------------------------------- 70C/W Lead Temperature (Soldering, 10 sec.)-------------------------------------------------------------------------- 260C Operation Temperature Range ------------------------------------------------------------------------------------ -40C to 85C Storage Temperature Range --------------------------------------------------------------------------------------- - 65C to 150C ESD Susceptibility (Note 2) HBM (Human Body Mode) ----------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
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(Note 3)
Ambient Temperature Range -------------------------------------------------------------------------------------- 0C to 70C Junction Temperature Range -------------------------------------------------------------------------------------- 0C to 125C
Electrical Characteristics
(VBAT = 1.8V, VOUT = 3.3V, TA = 25C, unless otherwise specified)
Parameter Start-Up Voltage Operating Voltage Range, After start-up VOUT Output Voltage Range VOUT Over Voltage Protection Switch-off Current I (VBAT) Shutdown Current Feedback Reference Voltage Switching Frequency Maximum Duty SWN Switch ON Resistance SWP Switch ON Resistance Current Limit Setting Error Amplifier GM Compensation Source Current Compensation Sink Current
Symbol VST VBAT VOUT_ADJ ISW OFF IOFF VFB FS D(MAX)
Test Conditions IL = 1mA
Min -1.1 2.4 ---0.784 ------
Typ 1.5 --6.5 200 0.01 0.8 650 85 210 240 2
Max -5.5 5.5 -350 1 0.816 ------
Units V V V V A A V kHz % m m A
VOUT = 3.3V, VFB = 0.9V EN Pin = 0V, Open Loop Close Loop, V OUT = 3.3V
VOUT = 3.3V VOUT = 3.3V ISW VOUT = 3.3V
----
0.2 22 22
----
ms uA uA
To be continued
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RT9278
Parameter Linear Controller Feedback Voltage for Linear Controller EN Input High Level Threshold EN Input Low Level Threshold Thermal Shutdown Thermal Shutdown Hysterises TSD TSD
Preliminary
Symbol Test Conditions Min Typ Max Units
VLFB
--0.4 ---
0.2 --180 20
-1.3 ----
V V V C C
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. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at T A = 25C on a high effective thermal conductivity test board of JEDEC 51-7 (2S2P, 4-Layers) thermal measurement standard.
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Preliminary Typical Operating Characteristics
Frequency vs. Temperature
700 680 0.804 0.803
RT9278
Reference Voltage vs. Temperature
Reference Voltage (V)
VDD = 3.3V
Frequency (kHz)
0.802 0.801 0.8 0.799 0.798 0.797
660 640 620 600 580 -40 -20 0 20 40 60 80 100 120 140 160 180
VDD = 3.3V
0.796 -40 -20 0 20 40 60 80 100 120 140 160 180
Temperature (C)
Temperature (C)
Efficiency vs. Output Current
Refer to Application Circuit Figure 3
100 90 80
Efficiency vs. Output Current
VOUT = 5.0V
90 80
VOUT = 3.3V
Efficiency (%)
60 50 40 30 20 10 0 1 10 100
Efficiency (%)
70
VIN VIN VIN VIN
= = = =
3.0V 2.5V 2.0V 1.5V
70 60 50 40 30 20 10 0 1 10 100
VIN VIN VIN VIN VIN VIN VIN
= = = = = = =
4.5V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V
1000
1000
Output Current (mA)
Output Current (mA)
Input Voltage vs. Output Voltage
3.350 3.325 5.150 5.100
Input Voltage vs. Output Voltage
Output Voltage (V)
3.300 3.275 3.250 3.225
Output Voltage (V)
5.050 5.000 4.950 4.900
VOUT = 3.3V
3.200 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 4.850
VOUT = 5.0V
1.6 1.925 2.25 2.575 1.93 2.58 2.9 3.225 3.55 3.875 3.23 3.88 4.2
Input Voltage (V)
Input Voltage (V)
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Refer to Application Circuit Figure 3
100
RT9278
Preliminary
Output Voltage vs. Output Current
3.310 3.305 3.300 3.295 3.290 3.285 3.280 3.275 3.270 3.265 3.260 3.255 3.250 1 10 100 1000 4.98 4.97 4.96
Output Voltage vs. Output Current
Output Voltage (V)
Output Voltage (V)
4.95 4.94 4.93 4.92 4.91 4.90 4.89 4.88 4.87 4.86 4.85 1
VIN VIN VIN VIN VOUT = 3.3V
= = = =
3.0V 2.5V 2.0V 1.5V
VOUT = 5.0V
10
VIN VIN VIN VIN VIN VIN VIN
= = = = = = =
4.2V 4.0V 3.5V 3.0V 2.5V 2.0V 1.5V
100 1000
Output Current (mA)
Output Current (mA)
Power LED Efficiency vs. Input Voltage
90
Normal Operation
Refer to Application Circuit Figure 1 VOUT
(10mV/Div) (5V/Div)
100
Power LED Efficiency (%)
80 70 60 50 40 30 20 10 0
VLX
(1V/Div)
VIN II N
(500mA/Div) VIN = 1.5V, VOUT = 5V, ILOAD = 100mA
Vf = 3.5V, ILED = 200mA, L = 4.7H
3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4 4.1 4.2 4.3
Time (1s/Div)
Input Voltage (V)
Normal Operation
VOUT
(10mV/Div) (5V/Div)
Normal Operation
VOUT
(10mV/Div)
VIN
(1V/Div)
VLX
(1V/Div)
VLX II N
VIN = 1.5V, VOUT = 5V, ILOAD = 300mA
(5V/Div) (500mA/Div) VIN = 4.2V, VOUT = 5V, ILOAD = 100mA
VIN II N
(1A/Div)
Time (1s/Div)
Time (1s/Div)
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DS9278-04 August 2007
Preliminary
RT9278
Load Transient Regulation
VIN = 1.5V, VOUT = 5V, ILOAD = 100mA to 300mA
Normal Operation
VOUT VIN
(1V/Div)
Load Current (mA) Output Voltage Deviation (mV)
VIN = 4.2V, VOUT = 5V, ILOAD = 300mA
(10mV/Div)
400 200 0
VLX
(5V/Div)
50 0 -50
II N
(500mA/Div)
Time (1s/Div)
Time (1ms/Div)
Load Transient Regulation
VIN = 4.2V, VOUT = 5V, ILOAD = 100mA to 400mA
Flash LED
VIN = 3.0V, Power LED = 200mA to 700mA
Load Current (mA)
400 200 0
VIN
(100mV/Div) (2V/Div)
GPIO Output Voltage Deviation (mV)
100 0 -100 (500mA /Div)
ILED II N Time (1ms/Div)
(500mA/Div)
Time (10ms/Div)
Flash LED
VIN = 3.77V, Power LED = 200mA to 700mA
Flash LED
VIN = 4.3V, Power LED = 200mA to 700mA
VIN
(100mV/Div) (2V/Div)
VIN
(100mV/Div) (2V/Div)
GPIO
(500mA /Div)
GPIO
(500mA/Div)
ILED II N
(500mA/Div) Mode Transition
ILED II N
(500mA/Div)
Time (10ms/Div)
Time (10ms/Div)
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RT9278
Application Information
Preliminary
RT9278 integrates a high-efficiency synchronous rectifier step-up DC-DC converter and a linear regulator controller. To fully utilize its advantages, peripheral components should be appropriately selected. The following information provides basic considerations for component selection. 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% 1 IPK = IIN(MAX) + IRIPPLE = 1.2 x IIN(MAX) 2 (IOUT(MAX) x VOUT = 1.2 x x VIN(MIN) The minimum inductance value is derived from the following equation: L= x IIN(MIN)2 x [VOUT - VIN(MIN)] 0.4 x IOUT(MAX) x VOUT 2 x fOSC
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 x ESRCOUT + Output Voltage Setting Referring to application circuits (Figure 6), the output voltage of the switching regulator (VOUT ) can be set with below equation : R2 VOUT = (1 + ) x VFB, R1 VFB = 0.8V (typ.) IPP 2x Cx f
Linear Regulator
Linear Regular MOSFETs Selection The linear controller of RT9278 was designed to drive an external P-Channel MOSFET. The main consideration of pass MOSFETs of linear regulator is package selection for efficient removal of heat. The power dissipation of a linear regulator is Plinear = (VIN-VOUT ) x IOUT (W)
Depending on the application, the recommended inductor value is between 2.2H and 10H. Input Capacitor Selection For better input bypassing, low-ESR ceramic capacitors are recommended for performance. A 10F input capacitor is sufficient for most applications. For a lower output power requirement application, this value can be decreased.
The criterion for selection of package is the junction temperature below the maximum desired temperature with the maximum expected ambient temperature. Layout Guide
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A full GND plane without gap break. VDD to GND noise bypass - Short and wide connection for the 1F MLCC capacitor between Pin7 and Pin3. VIN to GND noise bypass - Add a capacitor close to L1 inductor, when VIN is not an ideal voltage source. Minimized FB node copper area and keep far away from noise sources. The MOSFETs of linear regulator should have wide pad to dissipate the heat.
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Preliminary Outline Dimension
D2
RT9278
D
L
E
E2 SEE DETAIL A
1
e A A1 A3
b
2
1
2
1
DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated.
Symbol A A1 A3 b D D2 E E2 e L
Dimensions In Millimeters Min 0.800 0.000 0.175 0.180 2.950 2.300 2.950 1.500 0.500 0.350 0.450 Max 1.000 0.050 0.250 0.300 3.050 2.650 3.050 1.750
Dimensions In Inches Min 0.031 0.000 0.007 0.007 0.116 0.091 0.116 0.059 0.020 0.014 0.018 Max 0.039 0.002 0.010 0.012 0.120 0.104 0.120 0.069
V-Type 10L DFN 3x3 Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
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