RT9903GQV

Preliminary RT9903 5 Channel DC/DC Converters IC with High-Efficiency Step-Up General Description The RT9903 is a complete power-supply solution for digital still cameras and other hand-held devices. It integrates a high-efficiency fours step-up DC-DC converters and a charge pump. The two Step-up DC-DC converters (CH1,CH2) accept inputs from 1.5V to 5.5V and regulate a resistoradjustable output up t o 17V. On e Step-up DC-DC converter (CH3) can be regarded as white LED Driver, which reference voltage is 0.2V and have OVP function. One step-up DC-DC converter (CH4) regulate a resistoradjustable output up 5V. An adjustable operating frequency (up to 1.4MHz) is utilized to get optimum size, cost, and efficiency. The feature of the charge pump (CH5) is to deliver few current to CCD negative voltage. RT9903 is available in VQFN-24L 4x4 package. Each DC-DC converters have independent shutdown inputs. Features Two step-up DC-DC Converters (CH1, CH2) HV Internal Switches 50mA Load Current One Step-up DC-DC Converter (CH3) 0.2V Reference Voltage HV Internal Switches LED Brightness Dimming Control Over Voltage Protection One Step-up DC-DC Converter (CH4) External Switches External Current Limit Setting Step-up Charge Pump (CH5) for CCD Negative Voltage HV Internal Switches Up to 1.4MHz Switching Frequency 1μA Supply Current in Shutdown Mode External Compensation Network for All Converters Programmable Soft Start Function (CH1, CH2, CH3, CH4) I ndependent Enable Pin to Shutdown Each Channel 24-Lead VQFN Package RoHS Compliant and 100% Lead (Pb)-Free Applications Digital Still Camera PDAs Portable Device Ordering Information RT9903 Package Type QV : VQFN-24L 4x4 (V-Type) Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) Pin Configurations (TOP VIEW) COMP2 COMP1 19 18 17 16 FB2 AGND 21 24 23 22 CX INCD FB_CP RT EXT4 CS4 FB1 20 LX2 1 2 3 4 5 6 7 8 9 10 11 25 12 LX1 VDD PGND EN4 EN2 EN1 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. GND 15 14 13 COMP4 COMP3 FB4 FB3 LX3 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. DS9903-07 August 2007 VQFN-24L 4x4 EN3 www.richtek.com 1 RT9903 Typical Application Circuit 2-AA Battery 1.8V to 3.2V Preliminary VBATT C1 10uF D1 SS0520 C2 1uF L1 4.7uH 11 LX3 R1 4 WLED (12V) 17 VDD C15 4.7uF C16 10uF L3 4.7uH D3 SS0520 R9 2.2M C17 1nF R10 200k C18 10uF LX1 RT FB1 18 +12V (+LCD) 21 AGND 16 PGND 9 FB3 R15 10 C3 C4 VBATT 10uF 10uF L2 4.7uH R4 10k 6 CS4 Q1 Si2302 7 Chip Enable 13 14 12 15 19 23 10 8 R6 R7 2.2k 1.2k C12 C13 R8 2.7k C14 FB4 EN1 EN2 EN3 EN4 COMP1 COMP2 COMP3 COMP4 5 EXT4 RT9903 20 VBATT C19 10uF 3.3V_Motor R2 300k R3 130k D2 SS0520 C9 1nF LX2 24 L4 4.7uH D4 SS0520 R11 5.1M R12 360k C21 to C23 10uFx3 +15V (+CCD) C20 1nF FB2 22 C5 to C8 10uFx4 INCD 2 C24 68nF D5 SS0520 D6 SS0520 R13 750k R14 330k C27 1uF CX 1 -7.5V (-CCD) C25 to C26 10uFx2 FB-CP 3 C11 500pF R5 1.2k C10 4.7nF VCC 3.3V 6.8nF 56nF 4.7nF www.richtek.com 2 DS9903-07 August 2007 Preliminary V_3.3V VBATT C1 10uF WLED (12V) D1 SS0520 C2 1uF L1 4.7uH 11 LX3 R1 4 RT 21 AGND 16 PGND 9 FB3 R15 10 C3 C4 10uF 10uF VBATT L2 4.7uH 3.3V_Motor C5 to C8 10uFx4 R2 300k R3 130k Chip Enable D2 SS0520 C9 1nF R4 10k 6 Q1 Si2302 7 13 14 12 15 19 23 10 8 R6 R7 2.2k 1.2k C12 C13 R8 2.7k C14 FB4 EN1 EN2 EN3 EN4 COMP1 COMP2 COMP3 COMP4 INCD 2 C24 68nF D5 SS0520 D6 SS0520 R13 750k R14 330k C27 1uF 5 RT9903 C19 10uF 24 L4 4.7uH D4 SS0520 R11 5.1M R12 360k LX1 17 VDD C15 4.7uF C16 10uF L3 4.7uH D3 SS0520 R9 2.2M C17 1nF R10 200k C18 10uF RT9903 18 +12V (+LCD) FB1 20 VBATT LX2 CS4 EXT4 C21 to C23 10uFx3 +15V (+CCD) C20 1nF C28 FB2 22 CX 1 -7.5V (-CCD) C25 to C26 10uFx2 FB-CP 3 C11 500pF R5 1.2k C10 4.7nF VCC 3.3V 6.8nF 56nF 4.7nF Function Block Diagram COMP1 EN1 LX1 FB1 COMP2 EN2 LX2 FB2 INCD CX FBCP VDD CH1 V-Mode Step-Up PWM + CH2 V-Mode Step-Up PWM VREF 1V CH4 C-Mode Step-Up PWM 10uA + Charge Pump + - CH3 C-Mode Step-Up PWM AGND + - Thermal Protection Oscillator Soft Start RT - + VREF 0.2V COMP3 EN3 LX3 FB3 COMP4 EN4 EXT4 CS4 FB4 PGND (Exposed Pad) DS9903-07 August 2007 www.richtek.com 3 RT9903 Functional Pin Description Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Pin Name CX INCD FB_CP RT EXT4 CS4 FB4 COMP4 FB3 COMP3 LX3 EN3 EN1 EN2 EN4 PGND VDD LX1 COMP1 FB1 AGND FB2 COMP2 LX2 Preliminary Pin Function Charge Pump External Driver Pin. Charge Pump Input Pin. Charge Pump Feedback Pin. Frequency Setting Resistor Connection Pin. CH4 External Power Switch. CH4 Current Sense Input Pin. CH4 Feedback Input. CH4 Feedback Compensation Pin. CH3 Feedback Input. CH3 Feedback Compensation Pin. CH3 Switch Node. CH3 Enable Input Pin. CH1 Enable Input Pin. CH2 Enable Input Pin. CH4 Enable Input Pin. Power Ground. Power Input Pin. CH1 Switch Node. CH1 Feedback Compensation Pin. CH1 Feedback Input. Analog Ground. CH2 Feedback Input. CH2 Feedback Compensation Pin. CH2 Switch Node. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Exposed Pad (25) GND www.richtek.com 4 DS9903-07 August 2007 Preliminary Absolute Maximum Ratings (Note 1) RT9903 −0.3 to 7V −0.3V to 20V −0.3V to 7V 1.923W 52°C/W 260°C −40°C to 85°C 0°C to 125°C −65°C to 150°C Supply Input Voltage (VDD) --------------------------------------------------------------------------------------------LX1, LX2, LX3 Pins, INCD Pin ----------------------------------------------------------------------------------------Other I/O Pin Voltage ---------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C VQFN-24L 4x4 -----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 3) VQFN-24L 4x4, θJA ------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------------Operation Temperature Range ----------------------------------------------------------------------------------------Junction Temperature Range ------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------------- Recommended Operating Conditions (Note 2) Maximum Output Voltage Setting ( VOUT1 and VOUT2 ) ---------------------------------------------------------- 17V Dimming Control Frequency Range, CH3 -------------------------------------------------------------------------- 200Hz to 900Hz Electrical Characteristics (VDD =3.3V, TA = 25°C, unless otherwise specification) Parameter Supply Voltage VDD Operating Voltage VDD Start-up Voltage VDD Over Voltage Protection Supply Current Shutdown Supply Current CH1 DC/DC Converter Supply Current Symbol VVDD Test Condition VDD Pin Voltage VDD Pin Voltage Min 2.4 1.5 6 -- Typ ---0.01 Max 5.5 --1 Units V V V μA VDD(OVP) VDD Pin Voltage IOFF VDD = 3.6V, VEN1 to 4 = 0V VVDD =3.6V, IVDD1 VFB1 = VREF + 0.15V VEN1 = 3.3V, VEN2 = 0V, VEN3 = 0V, VEN4 = 0V VVDD = 3.6V, -- 200 250 μA CH2 DC/DC Converter & Charge Pump Supply Current IVDD2 VFB2 = VREF + 0.15V VEN1 = 0V, VEN2 = 3.3V, VEN3 = 0V, VEN4 = 0V VVDD = 3.6V, -- 210 260 μA CH3 DC/DC Converter Supply Current IVDD3 VFB3 = VREF + 0.15V VEN1 = 0V, VEN2 = 0V, VEN3 = 3.3V, VEN4 = 0V VVDD = 3.6V, -- 250 300 μA CH4 DC/DC Converter Supply Current IVDD4 VFB4 = VREF + 0.15V VEN1 = 0V, VEN2 = 0V, VEN3 = 0V, VEN4 = 3.3V -- 200 250 μA To be continued DS9903-07 August 2007 www.richtek.com 5 RT9903 Parameter Oscillator Free Running Frequency CH1, CH2, CH3 Maximum Duty Cycle CH4 Maximum Duty Cycle Preliminary Symbol FOSC DMAX1,2,3 DMAX4 VFB1, 2, 4 CH1, CH2, CH4 VFB3 VFBCP CH3 CH5 FB1 = COMP Test Condition RT = Open Min 400 93 75 0.98 0.18 -0.02 ---RDS1(ON) N-MOSFET, VDD = 3.3V RDS2(ON) N-MOSFET, VDD = 3.3V RDS3(ON) N-MOSFET, VDD = 3.3V -0.7 -0.7 -0.7 15 15 0.3 3 -VVDDM = 3.3V VVDDM = 3.3V ICS4 TSD -0.4 8 -Typ 500 95 80 1 0.2 0 200 22 22 0.6 -0.6 -0.6 -20 20 0.4 6 20 0.8 0.8 10 180 Max Units 600 -85 1.02 0.22 0.02 ---------25 25 0.5 9 -1.3 -12 -kHz % % V V V μs μA μA Ω A Ω A Ω A Ω Ω V Ω Ω V V μA °C Reference Voltage (CH1, CH2, CH3, CH4, CH5) Feedback Reference Voltage Feedback Reference Voltage Feedback Voltage (Charge Pump) Error Amplifier GM Compensation Source Current Compensation Sink Current Power Switch CH1 On Resistance of MOSFET CH1 Current Limitation CH2 On Resistance of MOSFET CH2 Current Limitation CH3 On Resistance of MOSFET CH3 Current Limitation Charge Pump On Resistance of N-MOSFET Charge Pump On Resistance of P-MOSFET CH4 Over Current Threshold Voltage CH4 On Resistance of N-MOSFET CH4 On Resistance of P-MOSFET Control EN1, EN2, EN3, EN4 Input High Level Threshold EN1, EN2, EN3, EN4 Input Low Level Threshold External Current Setting (CH4) CS4 Sourcing Current Thermal Protection Thermal Shutdown 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. The device is not guaranteed to function outside its operating conditions. Note 3. θJA i s measured in the natural convection at T A = 25 °C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 4. Pull low EN1, EN2 and EN4 when they are not enabled. EN3 pin is automatically pulled low when not enabled. www.richtek.com 6 DS9903-07 August 2007 Preliminary Typical Operating Characteristics CH1 Efficiency vs. Output Current 100 95 90 85 RT9903 VLX1 & Output Ripple VOUT = 12V VIN = 3.8V VIN = 4.5V Efficiency (%) VIN = 2.5V 75 70 65 0 5 10 15 VIN = 3V Output Ripple (50mV/Div) 30 35 40 45 50 80 LX1 (5V/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 30mA 20 25 Time (1us/Div) Output Current (mA) VLX1 & Output Ripple VLX1 & Output Ripple LX1 (5V/Div) Output Ripple (50mV/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 30mA Output Ripple (50mV/Div) LX1 (5V/Div) VBAT = 3.8V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) Time (1us/Div) VLX1 & Output Ripple 100 95 CH2 Efficiency vs. Output Current VOUT = 15V LX1 (5V/Div) Efficiency (%) 90 VIN = 3.8V VIN = 4.5V 85 80 75 Output Ripple (50mV/Div) VIN = 2.5V VIN = 3V VBAT = 4.2V, VDD = 3.3V, @IOUT = 30mA 70 0 5 10 15 20 25 30 Time (1us/Div) Output Current (mA) DS9903-07 August 2007 www.richtek.com 7 RT9903 VLX2 & Output Ripple Preliminary VLX2 & Output Ripple LX2 (5V/Div) Output Ripple (20mV/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 30mA Output Ripple (20mV/Div) LX2 (5V/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) Time (1us/Div) VLX2 & Output Ripple VLX2 & Output Ripple LX2 (5V/Div) Output Ripple (20mV/Div) VBAT = 3.8V, VDD = 3.3V, @IOUT = 30mA Output Ripple (20mV/Div) LX2 (5V/Div) VBAT = 4.2V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) Time (1us/Div) CH3 Efficiency vs. Input Voltage 100 VLX3 & Output Ripple 4 series WLED, ILED = 20mA Efficiency (%) 90 80 Output Ripple (100mV/Div) 2 2.4 2.8 3.2 3.6 4 4.4 85 LX3 (5V/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 20mA 95 75 Input Voltage (V) Time (1us/Div) www.richtek.com 8 DS9903-07 August 2007 Preliminary RT9903 VLX3 & Output Ripple LX3 (5V/Div) LX3 (5V/Div) VLX3 & Output Ripple Output Ripple (100mV/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 20mA Output Ripple (100mV/Div) VBAT = 3.8V, VDD = 3.3V, @IOUT = 20mA Time (1us/Div) Time (1us/Div) VLX3 & Output Ripple 100 CH4 Efficiency vs. Output Current VOUT = 3.3V LX3 (5V/Div) 95 Efficiency (%) VIN = 3V 90 Output Ripple (100mV/Div) 85 VIN = 2V VIN = 2.5V VBAT = 4.2V, VDD = 3.3V, @IOUT = 20mA 80 1 10 100 1000 Time (1us/Div) Output Current (mA) VLX4 & Output Ripple LX4 (2V/Div) LX4 (2V/Div) VLX4 & Output Ripple Output Ripple (20mV/Div) VBAT = 2V, VDD = 3.3V, @IOUT = 100mA Output Ripple (20mV/Div) VBAT = 2V, VDD = 3.3V, @IOUT = 350mA Time (1us/Div) Time (1us/Div) DS9903-07 August 2007 www.richtek.com 9 RT9903 Preliminary VLX4 & Output Ripple LX4 (2V/Div) LX4 (2V/Div) VLX4 & Output Ripple Output Ripple (20mV/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 100mA Output Ripple (20mV/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 350mA Time (1us/Div) Time (1us/Div) VLX4 & Output Ripple LX4 (2V/Div) LX4 (2V/Div) VLX4 & Output Ripple Output Ripple (20mV/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 100mA Output Ripple (20mV/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 350mA Time (1us/Div) Time (1us/Div) CH4 Load Transient Response Output Ripple (200mV/Div) Output Ripple (100mV/Div) CH4 Load Transient Response Output Current (200mA/Div) VBAT = 2V, VDD = 3.3V, @IOUT = 100mA to 350mA Output Current (200mA/Div) VBAT = 2.5V, VDD = 3.3V, @IOUT = 100mA to 350mA Time (1ms/Div) Time (1ms/Div) www.richtek.com 10 DS9903-07 August 2007 Preliminary RT9903 VCX & Output Ripple CH4 Load Transient Response Output Ripple (100mV/Div) Output Current (200mA/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 100mA to 350mA Output Ripple (20mV/Div) VBAT = 2.5V, VDD = 3.3V Time (1ms/Div) VCX (5V/Div) Time (2.5us/Div) VCX & Output Ripple VCX (5V/Div) VCX (5V/Div) VCX & Output Ripple Output Ripple (20mV/Div) VBAT = 3V, VDD = 3.3V Output Ripple (20mV/Div) VBAT = 3.8V, VDD = 3.3V Time (2.5us/Div) Time (2.5us/Div) VCX & Output Ripple 2500 Frequency vs. RRT Resistor VCX (5V/Div) 2000 Frequency (kHz)1 VBAT = 4.2V, VDD = 3.3V 1500 Output Ripple (20mV/Div) 1000 500 Time (2.5us/Div) 0 0 50 100 150 200 250 300 RRT (kΩ) DS9903-07 August 2007 www.richtek.com 11 RT9903 Application Information Preliminary Oscillator The internal oscillator synchronizes CH1, CH2, CH3 and CH4 PWM operation frequency. The operation frequency is set by a resistor between RT pin to ground, ranging from 500kHz to 1.4MHz. Step-up (Boost) DC/DC Converter (CH1) The channel (CH1) is a step-up voltage-mode DC/DC PWM converter with built-in internal power MOS and external schottky diode. Output voltage is regulated and adjustable up to 17V. This channel is designed to supply several tens mA current. The maximum duty of the constant frequency is 96% for this channel to prevent high input current drawn from input. The RT9903 is a five-Channel DC/DC converter for digital still cameras and other hand-held device. The five channels DC/DC converters are as follows: CH1: Step-up, asynchronous voltage mode DC/DC converter with an internal power MOSFET, current limit protection, and over voltage protection. This channel is designed to supply output voltage from 3.3V to 17V. CH2: Step-up, asynchronous voltage mode DC/DC converter with an internal power MOSFET, current limit protection, and over voltage protection. This channel is designed to supply output voltage from 3.3V to 17V. At the same time, it supplies the power for charge pump of CH5. CH3: Step-up, asynchronous current mode DC/DC converter with an internal power MOSFET, current limit protection, and over voltage protection. This channel is designed to light 2~4 WLEDs with constant current regulation, and the lightness can be dimming-controlled by the duty of EN3 pin. CH4: Step-up, asynchronous current mode DC/DC converter with current limit protection. This channel is designed to drive external N-MOS switch for steppingup voltage. CH5: Charge-pump, to supply negative voltage. This channel is enabled at the same time as CH2. Soft-Start CH1, CH2, and CH4 can be soft-started individually every time when the channel 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: TSOFT-START = (1V - 1uA x RCOMP) x CCOMP 1uA Protection 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 The over voltage protection prevents LX1 voltage going too high. The over-voltage is detected by the junction leakage and the threshold value is around 22V. This channel is latched shut down when OVP occurs, and can be reset by toggling EN1. Step-up (Boost) DC/DC Converter (CH2) The channel (CH2) is a step-up voltage-mode DC/DC PWM converter with built-in internal power MOS and external schottky diode. Output voltage is regulated and adjustable up to 17V. This channel is designed to supply several tens mA current. The output voltage of this channel supplies the power of charge-pump of CH5. The maximum duty of the constant frequency is 96% for this channel to prevent high input current drawn from input. RCOMP and CCOMP are compensation components. www.richtek.com 12 DS9903-07 August 2007 Preliminary Protection 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 The over voltage protection prevents LX2 voltage going too high. The over-voltage is detected by the junction leakage and the threshold value is around 22V. This channel is not latched shut down when OVP occurs. Step-up (Boost) DC/DC Converter (CH3) The channel (CH3) is a step-up current-mode DC/DC PWM converter with built-in internal power MOS and external schottky diode. This channel is designed to light 2 to 4 WLEDSs with constant current regulation. The lightness of WLED can be dimming-controlled by the duty of EN3 pin. The maximum duty of the constant frequency is 96% for this channel to prevent high input current drawn from input. RT9903 At light load, efficiency is enhanced by pulse-skipping mode. In this mode, the external NMOS turns on by a constant pulse width. As loading increased, the converter operates at constant frequency PWM mode. The maximum duty of the constant frequency is 80% for the boost to prevent high input current drawn from input. Protection Current Limit The current of NMOS is sensed cycle by cycle to prevent over current. The current is sensed by CS4 pin to determine whether it reaches current limit threshold. When CS4 voltage is higher than 0.4V, the external NMOS is off. This state is latched and then reset automatically at next clock cycle. V(CS4) = 10μA x RCS + IInductor x RDC(ON) External_MOS Current Mode Step-up Compensation When the step-up converter operates with continuous inductor current, the right-half-plane zero (RHPZ) appears in the loop-gain frequency response. To ensure the stability, the control-loop gain should crossover at the frequency (crossover frequency fC) much less than that of RHPZ. The inductor (L) and output capacitance (COUT) are chosen first in consideration of performance, size, and cost. The compensation resistor(RC) and capacitor(CC) are then chosen to optimize the control-loop stability. The useful steps are listed below to calculate loop compensation. Step-1 Calculate RHPZ For continuous conduction, the RHPZ is given by Protection 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 The over voltage protection prevents LX3 voltage going too high. The over-voltage is detected by the junction leakage and the threshold value is around 22V. This channel is latched shut down when OVP occurs, and can be reset by toggling EN3. Step-up (Boost) DC/DC Converter (CH4) The channel (CH4) is a step-up current-mode DC/DC PWM converter to drive external power N-MOS and external schottky diode. fRHPZ = VOUT (1-D)2 2π L IOUT Where D is the duty cycle = 1-(VIN / VOUT), L is the inductor value, and ILOAD is the maximum output current. Typical target crossover frequency is 1/6 of RHPZ. For example, if we assume VIN = 1.8V, VOUT = 3.3V, and IOUT = 0.5A, the RLOAD = 6.6Ω. If we select L = 4.7uH, then : fRHPZ = 66KHz DS9903-07 August 2007 www.richtek.com 13 RT9903 Step-2 Calculate CC Preliminary INCD ChargePump Driver CX CCP Negative Output Voltage COUT Choose fC = 10KHz, and then CC is calculated from the simplified loop-gain formula. Loop gain = Gm x 1 + SRCCC 1 ROUT VFB x x (1-D) x x SCC RCS 1+SROUTCOUT VOUT + - R1 FBCP R2 VDD Where Gm is the transconductance of error amplifier, and RCS is the current sense amplifier transresistance. In our design, Gm=200us, RCS = 0.8V/A, and VFB = 1V, and then CC = 4.34nF from calculation. Choose CC = 4.7nF. Step-3 Calculate RC RC is calculated such that transient droop requirements are met. For example, in our design, if 5% transient droop is allowed, then the error amplifier moves 0.05 x 1V, or 50mV. The error amplifier output drives 50mV x 200us, or 10uA across RC to provide transient gain. We select RCS = 2.7kΩ to meet the requirements. The output capacitor is chosed 40uF to cancel the RC CC zero, and can sustain stable VOUT voltage at heavy load condition. Charge Pump DC/DC Converter (CH5) This is a low quiescent negative-voltage charge pump DC/DC converter, which is enabled by EN2. Output ripple can be easily suppressed by increasing the capacitance ratio of COUT and CCP. This charge pump DC/DC converter can apply to negative voltage of CCD. The maximum output current is determined by the ratio of CCP and COUT. This equation would describe the relationship. IMAX = (VINCD − 2VF) x CCP x FCP VF : Schottky diode forward voltage FCP : Charge pump maximum frequency is 500kHz. The negative output voltage is set by R1 and R2. The FBCP threshold voltage is 0V. Reference The chip has an internal 1V reference voltage, which is the inputs of the error amplifiers of the CH1, CH2, and CH4 to compare the difference of feedback voltage. The reference voltage of CH3 is 0.2V for WLEDs application. The reference voltage can be set up stably when the supplied power (VDD) is above 1.5V, and EN1 (or EN2, EN3, EN4 either one) goes high. Thermal Protection Thermal protection function is integrated in the chip. When the chip temperature is higher than 180°C, the controllers of all channels are shutdown. When the thermal protection is relieved, the chip operates well again. VOUT x R2 VDD x R1 www.richtek.com 14 =1 DS9903-07 August 2007 Preliminary Outline Dimension D2 RT9903 D SEE DETAIL A L 1 E E2 1 2 1 2 e A A3 A1 b 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 3.950 2.300 3.950 2.300 0.500 0.350 0.450 Max 1.000 0.050 0.250 0.300 4.050 2.750 4.050 2.750 Dimensions In Inches Min 0.031 0.000 0.007 0.007 0.156 0.091 0.156 0.091 0.020 0.014 0.018 Max 0.039 0.002 0.010 0.012 0.159 0.108 0.159 0.108 V-Type 24L QFN 4x4 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 DS9903-07 August 2007 www.richtek.com 15