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Preliminary
RT9273
High Performance, OLED + LED Driver for Dual Panel Mobile Phone
General Description
The RT9273 is a high efficiency step-up DC-DC converter specifically designed for dual panel mobile phone applications. According to SP status, RT9273 can either regulates output current flowing through series-connected LEDs or regulate output voltage applying to OLED with a common output LC filter. This along with compact VDFN-10L 3x3 package and high switching frequency allows less part count and smaller external components for space and cost saving. Pulling low EN pin shuts down the chip and reduces the supply current to less than 1A. The EN pin also accepts PWM signal for LED brightness dimming control. The averaged LED current is well proportional to the duty cycle of the PWM signal. The internal soft start reduces inrush current during EN turning on or PWM dimming control. Other features include OVP, OCP and OTP. OVP prevents the damages in case of feedback loop open.
Features
Lion-Battery operating Range : 2.7V to 4.5V Maximum Output Voltage Up to 16V Share One Set of Inductor and Schottky Diode for 2 Channels Programmable Dimming Function by EN pin with 200Hz to 1kHz Internal Soft-Start Function to Avoid PWM Dimming Noise. Zero Shut Down Supply Current Complete Protection : OVP, OCP, OTP and SS RoHS Compliant and 100% Lead (Pb)-Free
Applications
Dual panel mobile phone, with LED backlight
Pin ConFigurations
(TOP VIEW)
GND FB2 CH2 VCC CH1
1 2 3 4 5 11 10 9 8 7 6
Ordering Information
RT9273 Package Type QV : VDFN-10L 3x3 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
LX SP OVP EN FB1
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.
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.
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RT9273
Typical Application Circuit
VIN CIN 2.2uF 4 VCC Chip Enable 7 EN L
Preliminary
DSH Schottky diode
OLED
10 LX OVP 8
VOUT COUT 2.2uF R2 300k
CH1 5 RT9273 CH2 3 9 SP 2 FB2 6 GND FB1 1
R1
R3
Figure 1. Dual panel 2LEDs + OLED mobile phone power solution
VIN
CIN 2.2uF 4 VCC
L
DSH Schottky diode 10 LX OVP 8 VOUT
OLED
COUT 2.2uF
Chip Enable 7 EN 9
R2 300k
CH1 5 RT9273 CH2 3 SP 2 FB2 6 GND FB1 1
R1
R3
Figure 2. Dual panel 3LEDs + OLED mobile phone power solution
VIN
CIN 2.2uF 4 VCC
L
DSH Schottky diode 10 LX OVP 8 VOUT
OLED
COUT 2.2uF
Chip Enable 7 EN
R2 300k
CH1 5 RT9273 CH2 3 9 SP 2 FB2 6 GND FB1 1
R1
R3
Figure 3. Dual panel 3LEDs + OLED mobile phone power solution. OLED is controlled by its driver to turn on/off.
Note: 1. Figure 1 is for PMOLED power ground connected to CH2 but not for OLED driver digital ground. 2. R3 = 7.68k for VOUT = 12V & 9.31k for VOUT = 10V 3. L: Measured by Murate LQH32C series 4.7H with DCR = 0.15 4. a. OLED turns on procedure: Firstly, EN pin pulls high and then SP pin pulls High. Finally set the OLED display to turn ON. b. OLED turns off procedure: Firstly set OLED display to turn OFF. And then SP pin pulls low but at the same time LED will turn on. Or keep the SP status and finally let the EN pin pull low. www.richtek.com 2 DS9273-09 August 2007
Preliminary Functional Pin Description
Pin No. 1 2 3 4 5 6 7 8 Pin Name GND FB2 CH2 VCC CH1 FB1 EN OVP Ground. Pin Function
RT9273
Feedback 2. Switching regulator feedback input. The feedback set point is 0.36V.Connect to a resistive divider between the switching regulator output and GND to adjust the output voltage as SP pin pull high. Channel 2. Internal FB loop. Connect the cathode of OLED to this pin. Voltage Input Pin. Bypass a 2.2uF capacitor to GND to reduce the input noise. Channel 1. Internal FB loop. Connect the cathode of LED to this pin. Feedback 1. Internal feedback voltage to set FB current of CH1 as SP pin pull low. Chip Enable Pin. Pull low or floating this pin to disable the system. Using a PWM signal on EN pin can achieve the dimming control. Over Voltage Protection. Detect over voltage condition and latch up the system until SP, EN or UVLO reset. Connect directly to the output capacitor. Selection Pin. Internal MOSFET selection. Pull low to turn on the internal CH1. Pull 9 SP high to turn on CH2. As SP input signal changes, internal MOSFET of LX pin will turn off 1ms to prevent the over voltage damage by the output voltage instant change. 10 LX Switch Pin. Connect this pin to inductor and schottky diode. Minimize the track area to reduce EMI. No Internal Connection.
Exposed Pad (11) NC
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RT9273
Function Block Diagram
VCC EN EN GT GND SP EN VRF
Preliminary
Dimming Controller
VCC EN VRF GND
OVP LX OVP ON FB Boost Controller GT
Buffer
CH1 CH2
1ms
5u FB1 FB2
Operation
RT9273 operates at a wide input voltage range suitable for Li-On battery and has a constant high frequency for smaller inductor and capacitors. The block diagram refers the operation circuit. The scheme is divided into three parts: dimming controller, boost controller and the logic selection function. By SP pin, it can choose the different channel to turn on CH1 or CH2. As the input signal change, internal MOSFET of LX pin will turn off 1ms to prevent the over voltage damage by the output voltage instant change. The Dimming Controller: RT9273 uses the PWM signal on EN pin to achieve dimming control. If the period of EN is less than 3ms in 50% duty, EN is always pulled high. Then EN signal is sent to the next boost controller to enable the function. This action is to differentiate between shut down and dimming control. VRF offers the reference voltage to error amplifier of next function. The internal soft start is designed for enable control and dimming control to avoid the inrush current. The Boost Controller: RT9273 uses current mode control scheme to provide better performance of line and load regulation. The boost controller includes of error amplifier, summing comparator, logic control and protection function. The difference between the feedback voltage and the reference voltage is send to the negative input of comparator. The comparator also senses the sensing current from inductor and slope compensation. To keep the output in regulation, the output of summing comparator is sent to the logic function, and then to control the duty ratio of the MOSFET switch. If the error amplifier's output increases, the duty of the switch will be larger to deliver more current to the output.
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Preliminary Absolute Maximum Ratings
(Note 1)
RT9273
Input Supply Voltage ----------------------------------------------------------------------------------------------------- -0.3V to 6V LX ---------------------------------------------------------------------------------------------------------------------------- -0.3V to 18V CH1, CH2, and OVP ----------------------------------------------------------------------------------------------------- -0.3V to 18V The Other Pins ------------------------------------------------------------------------------------------------------------ -0.3V to 6V Power Dissipation, PD @ TA = 25C, TJ = 125C VDFN-10L 3x3 ------------------------------------------------------------------------------------------------------------ 2.083W Package Thermal Resistance (Note 2) VDFN-10L 3x3, JA ------------------------------------------------------------------------------------------------------ 48C/W Operating Junction Temperature Range ----------------------------------------------------------------------------- -40C to 85C Junction Temperature Range ------------------------------------------------------------------------------------------- -40C to 125C Storage Temperature Range ------------------------------------------------------------------------------------------- -65C to 150C Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------ 260C
Recommended Operating Conditions
(Note 3) 2.7V to 4.5V Under 16V Under 80mA Under 1.28W
Input Supply Voltage ----------------------------------------------------------------------------------------------------Output Voltage -----------------------------------------------------------------------------------------------------------Output Current -----------------------------------------------------------------------------------------------------------Maximum Output Power ------------------------------------------------------------------------------------------------
Electrical Characteristics
(VCC = 3.7V, TA = 25C, Unless Otherwise specification)
Parameter System Supply Supply Current Shut Down Current Maximum Duty Cycle Reference Voltage Feedback Voltage 1 Feedback Voltage 2 Power Switch MOSFET On Resistance of MOSFET Current Limitation Internal MOSFET Selection On Resistance of CH1 MOSFET On Resistance of CH2 MOSFET SP Low Level Voltage SP High Level Voltage SP signal change delay time Protection OVP Threshold Over Temperature Protection Shut Down Voltage Enable Voltage
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Symbol ICC ICC
Test Condition VCC=3.7V, Switching, VFB=0V VCC=3.7V, VEN<0.4V
Min --85
Typ --90 0.300 0.300 0.5 1.5 6 4.0 --0.5 17 170 ---
Max 2 1 -0.315 0.315 1 -9 6 0.4 -1 19 -0.4 --
Units mA uA % V V A V V ms V C V V
VFB1 VFB2 RDS(ON) IMAX RDS(ON) RDS(ON) VSP VSP RDS(ON) OVP OTP VEN VEN LX off time as SP change Normal Operation
0.285 0.285 -----1.5 -16 --1.5
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RT9273
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 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. JA is measured in the natural convection at TA = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 3. The device is not guaranteed to function outside its operating conditions.
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Preliminary Typical Operating Characteristics
Efficiency vs. Input Voltage
90 0.9 89 0.89 88 0.88
ILED = 20mA
0.87 87 0.86 86
RT9273
Efficiency vs. Input Voltage
90 90% 89 89% 88 88% 87 87% 86 86% 85 85% 84 84% 83 83% 82 82% 81 81% 80 80%
3
Efficiency (%)
Efficiency (%)
ILED = 15mA ILED = 10mA
ILED = 20mA
85 0.85 84 0.84 83 0.83
0.82 82 0.81 81 0.8 80 3
ILED = 10mA
ILED = 15mA
Driving 2LEDs L = 4.7uH
3.15 3.3 3.45 3.6 3.75 3.9 4.05 4.2 4.35 4.5
Driving 3LEDs L = 4.7uH
3.15 3.3 3.45 3.6 3.75 3.9 4.05 4.2 4.35 4.5
Input Voltage (V)
Input Voltage (V)
Efficiency vs. Input Voltage
90 0.9 88 0.88
ILED = 20mA
0.86 86
Efficiency vs. Input Voltage
0.92 92 0.9 90 0.88 88 0.86 86
ILED = 10mA
ILED = 20mA
Efficiency (%)
Efficiency (%)
0.84 84 0.82 82 0.8 80 0.78 78 0.76 76 0.74 74 0.72 72 3
ILED = 10mA
0.84 84
82 0.82
0.8 80 0.78 78
76 0.76
ILED = 1mA Driving OLED L = 4.7uH, VOUT = 8.5V
3.15 3.3 3.45 3.6 3.75 3.9 4.05 4.2 4.35 4.5
0.74 74 0.72 72 0.7 70 3
ILED = 1mA Driving OLED L = 4.7uH, VOUT = 12V
3.15 3.3 3.45 3.6 3.75 3.9 4.05 4.2 4.35 4.5
Input Voltage (V)
Input Voltage (V)
Efficiency vs. Temperature
90% 90
350
Feedback Voltage vs. Temperature
340
Feedback Voltage(mV)
89% 89 88% 88
Driving OLED = 20mA
330 320 310 300 290 280 270 260 250 -40 -30 -20 -10 0
Efficiency (%)
87% 87
Driving 2LEDs
86% 86 85% 85 84% 84 83% 83
Driving 3LEDs Driving OLED
VIN = 3.4V
82% 82 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
VIN = 3.7V
10 20 30 40 50 60 70 80 90
Temperature (C)
Temperature (C)
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RT9273
Dimming Control
20
Preliminary
Dimming Control
14
Io-average Output Current (mA)
18 16 14 12 10 8 6 4 2 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Io-average Output Current (mA)
12 10 8 6 4 2 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1kHz 500Hz
1kHz 500Hz
200Hz Driving 2LEDs ILOAD = 20mA, VIN = 3.7V
200Hz
Driving 2LEDs ILOAD = 15mA, VIN = 3.7V
Duty
Duty
Dimming Control
9
13
Output Voltage vs. Output Current
Driving OLED L = 4.7uH, VIN = 3.7V, VOUT = 12.5V
Io-average Output Current (mA)
8 7 6 5 4 3 2 1 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8
12.8
1kHz 500Hz
Output Voltage (V)
Driving 2LEDs ILOAD = 10mA, VIN = 3.7V
12.6
12.4
200Hz
12.2
12 0 3 6 9 12 15 18 21 24 27 30
Duty
Output Current (mA)
Output Voltage vs. Output Current
9.1
Driving OLED L = 4.7uH, VIN = 3.7V, VOUT = 8.6V
8.9
Output Voltage (V)
8.7
8.5
8.3
8.1 0 3 6 9 12 15 18 21 24 27 30
Output Current (mA)
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Preliminary Application Information
Inductor Selection The recommended value of inductor for RT9273 applications is 4.7uH. Small size and better efficiency are the major concerns for portable device, such as RT9273 used for dual panel mobile phone. The inductor should have low DCR for better efficiency. To avoid inductor saturation, current rating should be at least 600mA for 3LEDs application in the input range 2.7V to 4.5V. Capacitor Selection 2.2F input output ceramic capacitors are recommended for RT9273 applications. 2.2uF input capacitor can reduce input ripple effectively. For better voltage stability, to increase the input capacitor value or using LC filter is feasible, especially in the Li-ion battery application. 1F output capacitor is sufficient to reduce output voltage ripple. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Diode Selection Schottky diode is a good choice for RT9273 because of its lower forward voltage drop and faster reverse recovery. Using schottky diode can get better efficiency. The highspeed rectification is also a good characteristic of schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following:
IDiode(RMS) ( IOUT x IPEAK )
RT9273
ILED (mA) 5 10 12 15 20 LEDs feedback resistor () 59 30.1 24.9 20 15
OLED output voltage control The output voltage can be set using a resistor-divider as Figure 2. To regulate the output resistor-divider (R2/R3) can get different output voltage of OLED as following formula.
VOUT = VFB (1 + R2 ) R3
Dimming Control Dimming control is the current programming method when output resistor fixes the brightness of LEDs. Using a PWM signal on EN pin can achieve the dimming control. RT9273 is turned on or off by the PWM signal applied to EN pin. The brightness of LEDs is depended on PWM duty cycle. The average LED current increases proportionally as the duty cycle added. The average LED current is linear in different duty cycle. It should be notice that the magnitude of PWM signal should be higher than the minimum EN voltage. The recommended dimming frequency is 200Hz to 1kHz.
Dimming Control for 3LEDs
VIN = 3.7V
The diode's reverse breakdown voltage should be larger than the output voltage. SS0520 is recommended schottky diode for rectifier. LED Current Control Current control is to change different brightness of LEDs. To regulate the output resistor can get different currents of LEDs as following formula. The table for the selection of feedback resistor is shown below. LEDs Feedback_r esistor = 0.3V ILED
VEN (5V/Div) LX (5V/Div) VOUT (5V/Div) IOUT (20mA/Div) Time (2ms/Div)
Figure 4
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RT9273
Channel Selection
Preliminary
There is one set of LC filter for RT9273 to share two channels power requirement. Each time turning on only one channel can save the power dissipation and easily extend the standby time. Selection pin is internal logic controller. SP pin is pulled low to turn on the internal channel 1 (for LED) and pulling high to turn on channel 2 (for OLED). As the input signal change, internal MOSFET of LX pin will turn off 1ms to prevent the over voltage damage by the output voltage instant change. Logic control and application circuit for LEDs and OLED turning on simultaneously + 2 modes dimming control To achieve LEDs and OLED turning on simultaneously, the following application circuit (Figure 5) provides the complete solution by simple logic control (Table 1). Formula:
VOUTH = ILEDH = R3 = R2 + (R8//R7) x VFB2 ; VOUTL = R2 + R7 x VFB2 (R8//R7) R7
VFB1 V ; ILEDL = FB1 (R5//R6) R5
VOUT - 3VF(LED) ILED
CIN 2.2uF L1 4.7uH COUT 2.2uF OLED R3 300 WLED_ON CH2 FB2 GND FB1 R5 82 R6 20 R7 24k R8 100k Dimm
VIN
SS0520
VCC R1 4.7k
LX OVP
R2 1M
WLED_ON
EN
CH1 RT9273
EL_ON
SP
Figure 5. Application circuit for LED and OLED turning on simultaneously Table 1. Truth table for Figure 5 WLED_ON EL_ON DIMM
M & S turn on simultaneously Normal M & S turn on simultaneously Dimming Main ONLY Normal Main ONLY Dimming Sub ONLY Normal Sub ONLY Dimming SHUT DOWN H -H H L L L H -L L H H L H -H L H L Don't care
Function VOUT = 16V, ILED = [VOUT - 3VF(LED)]/R3 mA -VOUT = 9.5V, ILED = 18.5 mA VOUT = 9.5V, ILED = 3.6 mA VOUT = 13V, ILED = 0 mA VOUT = 16V, ILED = 0 mA VOUT = 0V, ILED = 0 mA
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Preliminary
RT9273
Logic control and application circuit for LED and OLED turning on simultaneously + PWM dimming control for LED To achieve LEDs and OLED turning on simultaneously, the following application circuit (Figure 6) provides another solution by simple logic control (Table 2).
VIN
CIN 2.2uF
L1 4.7uH
SS0520
COUT 2.2uF OLED R3 300 WLED_ON R5 16 R6 24k
VCC R1 4.7k EN
LX OVP CH1
R2 1M
WLED_ON
RT9273 EL_ON SP CH2 FB2 FB1 GND
R7 100k Dimm
Figure 6. Application circuit for LED and OLED turning on simultaneously Table 2. Truth table for Figure 6
WLED_ON M & S turn on simultaneously Normal M & S turn on simultaneously Dimming Main ONLY Normal Main ONLY Dimming Sub ONLY Normal Sub ONLY Dimming SHUT DOWN H -H PWM L L L EL_ON H -L L H H L DIMM H -H H H L Don't care Function VOUT = 16V, ILED = [VOUT - 3VF(LED)]/R3 mA -VOUT = 9.5V, ILED = 18.5 mA V OUT = 9.5V, ILED = depends on PWM VOUT = 13V, ILED = 0 mA VOUT = 16V, ILED = 0 mA VOUT = 0V, ILED = 0 mA
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RT9273
Preliminary
Logic control and application circuit for LED and OLED 2 level dimming control Besides using a PWM signal on EN pin, using logic control can also achieve LEDs and OLED 2 modes dimming control function. The following application circuit (Figure 7) provides another solution by simple logic control (Table 3). Formula:
ILED (MIN) = ILED (MAX) = VOLED = VFB1 0.3V (typ.) = R4 R4 0.3V (typ.) VFB1 = R4//R5 R4//R5
R1+ (R2//R3) R1//R2 x (VFB Vd) (R2//R3) R3 + (R1//R2)
VFB = 0.3 (typ.), If Vd_low = 0V, Vd_high = 2.8V, VOLED_high = 16.3V, VOLED_low = 13V. Firstly to set R1=100k, and then get R2 = 1.92k, R3 = 84.85k Note: The recommended R1 value is 100k. Choosing R1's value 100k is proper to the application circuit.
VIN
CIN 2.2uF
L1 4.7uH
SS0520
COUT 2.2uF
VOUT
OLED
16.3V 13V R1 100k
VCC Chip Shutdown EN Chip Enable SP
LX OVP CH1
RT9273 CH2 FB2 FB1 GND R4 150 R5 18 Dimm 2.8V 0V R3 84.85k R2 1.92k
Figure 7. Application circuit for LED and OLED 2 level dimming control respective Table 3. Truth table for Figure 7
EN Main ONLY NORMAL Main ONLY DIMMING Sub ONLY NORMAL Sub ONLY DIMMING SHUT DOWN H H H H L SP L L H H Don't care DIMM H_2.8V/ L_0V H L L H Don't care Function ILED = 18mA ILED = 2mA VOUT = 16.3V, ILED = 0mA VOUT = 13V, ILED = 0mA --
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Preliminary
Layout Guide A full GND plane without gap break. The input capacitor should be placed as close as possible to the input for good filtering. The switching path should be shorter to prevent EMI problems. The inductor and diode must be placed closely to the switch pin. The feedback path should be away from the inductor. The feedback resistor should be connected directly to the GND.
RT9273
Figure 8. Top Layer
Figure 9. Bottom Layer
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RT9273
Outline Dimension
Preliminary
D
D2
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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DS9273-09 August 2007

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