RT9284A/B. Tiny Package, High Performance, Constant Current Switching Regulator for White LED. General Description. Features.

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1 Tiny Package, High Performance, Constant Current Switching Regulator for White LED RT98A/B General Description The RT98A/B is a compact, high efficient and high integration LED driver. Internal V MOSFET can support to White LEDs for backlighting and camera flashing. Highly integration and internal compensation network minimizes as external component counts. Optimized operation frequency can meet the requirement of small LC filters value and low operation current with high efficiency. Internal soft start function can reduce the inrush current. Tiny package type of TSOT-3- and TSOT-3- packages provide the best solution for PCB space saving and total BOM cost. Features Operating Range :.7V to.v Maximum Output Voltage up to 0V Dimming with Zero-inrush and Wide Frequency Range of 00 to 00kHz Over Voltage Protection Output Current up to 00mA at V OUT : V Zero Shutdown Supply Current Minimize the External Component Small LC Filter Internal Soft Start RoHS Compliant and 00% Lead (Pb)-Free Ordering Information RT98 (- ) Package Type J : TSOT-3- J : TSOT-3- Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Voltage : V 0 : 0V Applications Camera Flash White LED Mobile Phone, Smart Phone LED Backlight PDA LED Backlight Digital Still Camera Camcorder Pin Configurations TOP VIEW VDD Voltage A :.3V B : 0.V Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-00. Suitable for use in SnPb or Pb-free soldering processes. Marking Information For marking information, contact our sales representative directly or through a Richtek distributor located in your area. 3 GND TSOT-3- VDD 3 GND TSOT-3- DS98A/B-07 April 0

2 Typical Application Circuit L.7uH to uh D SS00 V V + IN.7V to.v C uf RT98 VDD C uf/v I LED Dimming Control 00Hz-00kHz GND 3 R Figure. Application for Driving 3 Series WLEDs L.7uH to uh D SS00 8V V + IN.7V to.v C uf RT98 VDD R 00k C uf/v I LED Dimming Control 00Hz-00kHz GND V 3 R Figure. Application for Driving Series WLEDs L.7uH to uh D SS00 0V V + IN.7V to.v C uf RT98B VDD C uf/v I LED Dimming Control 00Hz-00kHz GND 3 V = 0.V R Figure 3. Application for Driving Series WLEDs V + IN.7V to.v C uf L.7uH to uh RT98A VDD D SS00 V R 30k V OUT V C uf/v GND 3 V =.3V R k Figure. Application for Constant Output Voltage DS98A/B-07 April 0

3 Pin Description Pin No. TSOT-3- TSOT-3- Pin Name GND Ground Pin VDD Pin Function RT98A/B Switch Pin. Connect this Pin to inductor and catch diode. Minimize the track area to reduce EMI. Feedback Reference Voltage Pin. Series connect a resistor between WLED and ground as a current sense. Sense the current feedback voltage to set the current rating. Chip Enable (Active High). Voltage sensing input to trigger the function of over voltage protection. Note that this pin is high impedance. There should be a pull low 00kΩ resistor connected to GND when the control signal is floating. Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage protection. Leave it unconnected to disable this function. Supply Input Voltage Pin. Bypass uf capacitor to GND to reduce the input noise. Function Block Diagram.MHz OSC VDD Current Bias BandGap ibias V REF OCP 70mA PWM Logic Protection Circuit + - Buffer UVLO + Timer ms Soft Start - V REF GND DS98A/B-07 April 0 3

4 Absolute Maximum Ratings (Note ) Supply Input Voltage V to 7V Input Voltage V to V Voltage V to V The Other Pins V to V Power Dissipation, P T A = C TSOT W TSOT W Package Thermal Resistance (Note ) TSOT-3-, θ JA C/W TSOT-3-, θ JA C/W Lead Temperature (Soldering, 0 sec.) C Junction Temperature C Storage Temperature Range C to 0 C ESD Susceptibility (Note 3) HBM (Human Body Mode) kv MM (Machine Mode) V Recommended Operating Conditions (Note ) Supply Input Voltage V to.v Junction Temperature Range C to C Ambient Temperature Range C to 8 C Electrical Characteristics (VIN = 3.7V, TA = C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit System Supply Input Operation voltage Range V DD V Under Voltage Lock Out V DD.8.. V Quiescent Current I DD =.V, No switch ua Supply Current I DD = 0V, Switch 0. 3 ma Shut Down Current I DD V < 0.V ua Line Regulation : 3.0~.3V % Oscillator Operation Frequency f OSC MHz Maximum Duty Cycle % Dimming Frequency k Hz Reference Voltage Feedback Voltage (Note ) RT98A RT98B V To be continued DS98A/B-07 April 0

5 Parameter Symbol Test Condition Min Typ Max Unit MOSFET On Resistance of MOSFET R DS(ON) Ω Protection Threshold V Note. 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. θja is measured in the natural convection at TA = C on a low effective thermal conductivity test board of JEDEC -3 thermal measurement standard. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note. The device is not guaranteed to function outside its operating conditions. Note. Floating the pin to disable function. for,3, WLEDs application for WLED application 9 0 Sink Current μa OCP ma Shut Down Voltage V V Enable Voltage V V V DS98A/B-07 April 0

6 Typical Operating Characteristics. Enable Voltage vs. Input Voltage. Shut Down Voltage vs. Input Voltage Enable Voltage (V) C C 8 C Shut Down Voltage (V) C C 8 C Input Voltage (V) Input Voltage (V) Efficiency vs. Input Voltage ILED = 0mA, L =.7μH, DCR = 0.Ω. LED Current vs. Input Voltage WLEDs, L = 0μH Efficiency (%) WLEDs WLEDs LED Current (ma) Input Voltage (V) Input Voltage (V) 9% Maximum Duty Cycle vs. V DD.7 POR (Rising/Falling) vs. Temperature Maximum Duty Cycle (%) 90% 89% 88% 87% 8% POR (V) Rising Falling 8% V DD (V) Temperature ( C) DS98A/B-07 April 0

7 Switching Current vs. Input Voltage. Switching Frequency vs. Temperature Switching Current (ma) C C 8 C Switching Frequency (MHz) Input Voltage (V) Temperature ( C). Feedback Voltage vs. Temperature Dimming Operation WLEDs, VIN = 3.7V, ILED = 0mA, L = 0μH Feedback Voltage (mv) Temperature ( C) ILED (0mA/Div) (0mA/Div) f = 00Hz, Duty = 0% Time (ms/div) Dimming Operation Dimming Operation WLEDs, VIN = 3.7V, ILED = 0mA, L = 0μH WLEDs, VIN = 3.7V, ILED = 0mA, L = 0μH (00mA/Div) (00mA/Div) (0mA/Div) I LED (0mA/Div) f = khz, Duty = 0% I LED f = 0kHz, Duty = 0% Time (00μs/Div) Time (0μs/Div) DS98A/B-07 April 0 7

8 Dimming Operation WLEDs, VIN = 3.7V, ILED = 0mA, L = 0μH L = 0μH OCP (0V/Div) VOUT IIN (00mA/Div) I (00mA/Div) ILED (0mA/Div) f = 00kHz, Duty = 0% (0V/Div) Time (μs/div) Time (μs/div) Inrush Current Inrush Current WLEDs, VIN = 3.0V, ILED = 0mA, L =.7μH WLEDs, VIN =.3V, ILED = 0mA, L =.7μH (V/Div) (V/Div) (V/Div) (V/Div) VOUT VOUT (00mA/Div) (00mA/Div) Time (00μs/Div) Time (00μs/Div) Normal Operation Normal Operation V OUT (V/Div) (0V/Div) WLEDs, VIN = 3.0V ILED = 0mA, L = 0μH V OUT (V/Div) (0V/Div) WLEDs, VIN = 3.7V ILED = 0mA, L = 0μH (00mA/Div) (00mA/Div) Time (00ns/Div) Time (00ns/Div) DS98A/B-07 April 0 8

9 Normal Operation Normal Operation V OUT (V/Div) (0V/Div) WLEDs, VIN =.3V ILED = 0mA, L = 0μH VOUT (V/Div) (0V/Div) WLEDs, VIN =.V ILED = 0mA, L = 0μH (00mA/Div) IIN (00mA/Div) Time (00ns/Div) Time (00ns/Div) DS98A/B-07 April 0 9

10 Application Information Power Sequence The RT98A/B must take notice of the power sequence. The power sequence of RT98A/B has to VDD early than or else the RT98A/B maybe fall into the unknown state to result in RT98A/B turn off. V DD >.7V V DD >.V < 0.V V OUT Figure LED Current Control The RT98A/B regulates the LED current by setting the current sense resistor (R) connecting to feedback and ground. As shown in Table, the RT98A feedback voltage (V ) is.3v and the RT98B feedback voltage (V ) is 0.V. The LED current (I LED ) can be set by a resistor R. In order to have an accurate LED current, a precision resistor is preferred (% is recommended). Table Feedback Reference LED Current Version Voltage V (V) Setting I LED (A) RT98A.3 I LED =.3/R RT98B 0. I LED = 0./R Dimming Control a. Using a PWM Signal to Pin For controlling the LED brightness, the RT98A/B can perform the dimming control by applying a PWM signal to pin. The internal soft start and the wide range dimming frequency from00 to00khz can eliminate inrush current and audio noise when dimming. The average LED current is proportional to the PWM signal duty cycle. The magnitude of the PWM signal should be higher than the maximum enable voltage of pin, in order to let the dimming control perform correctly. b. Using a DC Voltage Using a variable DC voltage to adjust the brightness is a popular method in some applications. The dimming control using a DC voltage circuit is shown in Figure. According to the Superposition Theorem, as the DC voltage increases, the voltage contributed to V increases and the voltage drop on R decreases, i.e. the LED current decreases. For example, if the V DC range is from 0V to.8v, the selection of resistors in Figure sets dimming control of LED current from 0mA to 0mA..7V to.v C V >.V V < 0.V L.7uH to uh RT98A VDD GND 3 D SS00 R3 3k V DC Dimming 0V to.8v Figure. Dimming Control Using a DC Voltage for RT98A c. Using a Filtered PWM signal: C R 0k R 0 I LED The LED current can be calculated by the following equation. V I = LED R (VDC V ) R3 R Another common application is using a filtered PWM signal as an adjustable DC voltage for LED dimming control. A filtered PWM signal acts as the DC voltage to regulate the output current. The recommended application circuit is shown in the Figure 7. In this circuit, the output ripple depends on the frequency of PWM signal. For smaller output voltage ripple (<00mV), the recommended frequency of.8v PWM signal should be above khz. To fix the frequency of PWM signal and change the duty cycle of PWM signal can get different output current. Figure 8. shows the relationship between LED current and PWM duty cycle. DS98A/B-07 April 0 0

11 .7V to.v Figure 7. Filtered PWM Signal for LED Dimming Control of RT98A The LED current can be calculated by the following equation. LED Current (ma) R (VPWM Duty V ) V R3 + RDC I LED = R C V >.V V < 0.V L.7uH to uh RT98A VDD GND 3 D SS PWM Duty (%) R3 0k R DC 3k.8V 0V PWM Signal C R 0k C DC uf R 0 I LED Capacitor Selection Input and output ceramic capacitors of μf are recommended for RT98A/B applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. XR and X7R types are suitable because of their wider voltage and temperature ranges. Diode Selection Schottky diode is a good choice for RT98A/B because of its low forward voltage drop and fast 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 : ID (RMS) (IOUT I PEAK ) The diode s reverse breakdown voltage should be larger than the output voltage. SS00 is recommended Schottky diode for rectifier. Layout Guide A full GND plane without gap break. VCC to GND noise bypass Short and wide connection for the μf MLCC capacitor between Pin and Pin. Minimized node copper area to reduce EMI. Minimized node copper area and keep far away from noise sources. Figure 8 Inductor Selection The recommended value of inductor for 3 to WLEDs applications are.7 to μh. Small size and better efficiency are the major concerns for portable device, such as RT98A/B used for mobile phone. The inductor should have low core loss at.mhz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Figure 9. Top Layer DS98A/B-07 April 0

12 Figure 0. Bottom Layer DS98A/B-07 April 0

13 Outline Dimension D H L C B b A e A Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A B b C D e H L TSOT-3- Surface Mount Package DS98A/B-07 April 0 3

14 D H L C B b A A e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A A B b C D e H L TSOT-3- Surface Mount Package Richtek Technology Corporation Headquarter F, No. 0, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (883)789 Fax: (883) Richtek Technology Corporation Taipei Office (Marketing) F, No. 9, Minchiuan Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (88)87399 Fax: (88) marketing@richtek.com Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. DS98A/B-07 April 0