RT9272

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 1μA. 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 40μA 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 P ackage 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 DS9272-09 August 2007 www.richtek.com 1 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 4.7μH with DCR = 0.15Ω 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 www.richtek.com 2 DS9272-09 August 2007 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. DS9272-09 August 2007 www.richtek.com 3 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 = 25°C, TJ = 125°C VDFN-10L 3x3 ---------------------------------------------------------------------------------------------------------- 2.083W Package Thermal Resistance (Note 2) VDFN-10L 3x3, θJA ---------------------------------------------------------------------------------------------------- 48°C/W Operating Junction Temperature Range -------------------------------------------------------------------------- −40°C to 85°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C 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 = 25°C, 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