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Preliminary
RT9272
High Performance, Constant Current LED Driver for Dual Panel Mobile Phone
General Description
The RT9272 is a high efficiency step-up DC-DC converter specifically designed for dual panel mobile phone applications. According to SP status, RT9272 can either regulates output current flowing through series-connected LEDs for main panel or for sub panel 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
Low VIN Operating Range : 2.7V to 4.5V Maximum Output Voltage up to 16V Small LC filter by 1.1MHz Operation Frequency Share One Set of Inductor and Schottky Diode for 2 Channels Programmable Dimming Function by EN Pin with 100Hz to 1kHz 40A Quiescent Current (Switch-Off) 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
RT9272 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
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.
VIN
Typical Application Circuit
CIN 2.2uF L 4.7uF SS0520 DSH COUT 1uF
Sub-Panel Main Panel
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.
4 10 VCC LX RT9272 Chip Enable 8 OVP 7 EN 5 CH1 9 3 SP CH2 R1 6 2 R2 FB2 FB1 GND 1
Figure 1. 2LEDs for Sub panel and 3LEDs for Main panel
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RT9272
VIN CIN 2.2uF
Preliminary
L 4.7uF SS0520 DSH COUT 1uF
Sub-Panel
Main Panel
4 10 VCC LX RT9272 Chip Enable 8 OVP 7 EN 5 CH1 9 3 SP CH2 R1 6 2 R2 FB2 FB1 GND 1
Figure 1. 2LEDs for Sub panel and 4LEDs for Main panel
Note: L : Measured by Murate LQH32C_53 series 4.7H with DCR = 0.15
Functional Pin Description
Pin No. 1 2 3 4 5 6 7 8 Pin Name GND FB2 CH2 VCC CH1 FB1 EN OVP Ground. Feedback 2. Internal feedback voltage to set FB current of Ch2 as SP pin pull high. Channel 2. Internal FB loop. Connect the cathode of LED 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 CE pin can achieve the dimming control. Over Voltage Protection. Detect over voltage condition and latch 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 change, 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. Pin Function
Exposed Pad (11) NC
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Preliminary Function Block Diagram
RT9272
VCC EN EN GT GND SP
1ms
EN VRF
Dimming Controller
VCC EN VRF GND
OVP LX OVP ON FB Boost Controller GT
Buffer
CH1 CH2
5u FB1 FB2
Operation
RT9272 operates at a wide input voltage range suitable for Li-ion 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: RT9272 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: RT9272 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. As SP switches, the channel will be changed for 2LEDs output or 3LEDs output. 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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RT9272
Absolute Maximum Ratings
Preliminary
(Note 1)
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 Storage Temperature Range ---------------------------------------------------------------------------------------- -65C to 150C Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260C
Recommended Operating Conditions
(Note 3)
Input Supply Voltage -------------------------------------------------------------------------------------------------- 2.7V to 4.5V Output Voltage --------------------------------------------------------------------------------------------------------- Under 16V Output Current --------------------------------------------------------------------------------------------------------- Under 80mA
Electrical Characteristics
(VIN = 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
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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Preliminary
RT9272
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 T A = 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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RT9272
Typical Operating Characteristics
Preliminary
Efficiency vs. Input Voltage
89 88 87 86
Quiescent Current vs. VCC
0.25 0.24
L = 4.7uH, DCR = 0.15
VFB = 1V
2LEDs
Quiescent Current (mA)
0.23 0.22 0.21 0.2 0.19 0.18 0.17 0.16 0.15
Efficiency (%)
85 84 83 82 81 80 79 78 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
4LEDs
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
Input Voltage (V)
VCC (V)
Supply Current vs. VCC
2.1 1.9
VFB vs. VCC
0.33 0.32 0.31
VFB = 0V
Supply Current (mA)
1.7
1.3 1.1 0.9 0.7 0.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
V FB (V)
1.5
0.3 0.29 0.28 0.27 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
VCC (V)
VCC (V)
VFB vs. Temperature
0.315 0.3125
EN Pin Voltage vs. Input Voltage
1.6 1.4
V FB (V)
0.3075 0.305 0.3025 0.3 0.2975 0.295 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
EN Pin Voltage (V)
0.31
1.2 1.0 0.8 0.6 0.4 0.2 0.0 2.7 2.9 3.1 3.3 3.5
VIH
VIL
3.7
3.9
4.1
4.3
4.5
Temperature (C)
Input Voltage (V)
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Preliminary
RT9272
Dimming Control for 4LEDs
18
SP Voltage vs. Input Voltage
1.4
Io - Average Output Current (mA)
VIN = 3.7V, ILED = 20mA
16 14 12 10 8 6 4 2 0 20 30 40 50 60 70 80
1.2 1
V IH
SP Voltage (V)
VIL
0.8 0.6 0.4 0.2 0 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5
100kHz 200Hz 500Hz 1kHz
Input Voltage (V)
Duty (%)
Dimming Control for 3LEDs
18
Dimming Control for 2LEDs
20
Io - Average Output Current (mA)
Io - Average Output Current (mA)
VIN = 3.7V, ILED = 20mA
16 14 12 10 8 6 4 2 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8
18 16 14 12 10 8 6 4 2 0
VIN = 3.7V, ILED = 20mA
1kHz 500Hz 200Hz 100Hz
1kHz 500Hz 200Hz 100Hz
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Duty (%)
Duty (%)
Dimming Operation for 3LEDs
Dimming Operation for 3LEDs
EN (2V/Div)
EN (2V/Div)
VOUT (5V/Div)
VOUT (5V/Div)
ILED (10mA/Div)
VIN = 3.7V, f = 100Hz, Duty = 50%
ILED (10mA/Div)
VIN = 3.7V, f = 1kHz, Duty = 50%
Time (4ms/Div)
Time (400s/Div)
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RT9272
OVP
Preliminary
VIN = 3.7V VOUT (5V/Div)
LX (10V/Div)
IL (500mA/Div)
Time (400s/Div)
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Preliminary Application Information
Inductor Selection The recommended value of inductor for RT9272 applications is 4.7H. Small size and better efficiency are the major concerns for portable device, such as RT9272 used for dual panel mobile phone. The inductor should have low DCR for better efficency. 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 and 1F output ceramic capacitors are recommended for RT9272 applications. 2.2uF input capacitor can reduce input ripple. 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 RT9272 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 )
RT9272
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. RT9272 is turned on or off by the PWM signal applied to EN pin. The brightness of LEDs for CH1 or CH2 is depended on PWM duty cycle. By selecting the different channel, it can achieve the dimming control function for main panel or sub panel. The average LED current increases proportionally as the duty cycle added. The operation frequency of PWM signal is 100Hz to 1kHz. 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. Channel Selection There is one set of LC filter for RT9272 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 and pulling high to turn on channel 2. 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. 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.
The diode'sreverse 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. FB_resister ( ) = 0.3 (V) ILED (mA)
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RT9272
Preliminary
Figure 1. Top Layer
Figure 2. Bottom Layer
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DS9272-09 August 2007
Preliminary Outline Dimension
D2
RT9272
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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