RT9903 Preliminary 5 Channel DC/DC Converters IC with High-Efficiency Step-Up General Description Features 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 z Two step-up DC-DC Converters (CH1, CH2) `HV Internal Switches `50mA Load Current charge pump. z One Step-up DC-DC Converter (CH3) `0.2V Reference Voltage `HV Internal Switches `LED Brightness Dimming Control `Over Voltage Protection z 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 1μ μA Supply Current in Shutdown Mode External Compensation Network for All Converters Programmable Soft Start Function (CH1, CH2, CH3, CH4) Independent Enable Pin to Shutdown Each Channel 24-Lead VQFN Package RoHS Compliant and 100% Lead (Pb)-Free z z Digital Still Camera PDAs Portable Device Ordering Information z z z z Pin Configurations RT9903 (TOP VIEW) 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. 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 COMP2 FB2 AGND FB1 COMP1 24 23 22 21 20 19 CX 1 18 LX1 INCD 2 17 VDD FB_CP 3 16 PGND RT 4 15 EN4 EXT4 5 14 EN2 CS4 6 13 EN1 GND 25 7 FB4 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) LX2 Package Type QV : VQFN-24L 4x4 (V-Type) 8 9 10 11 12 LX3 z z EN3 Applications z COMP3 RT9903 is available in VQFN-24L 4x4 package. Each DC-DC converters have independent shutdown inputs. z FB3 The feature of the charge pump (CH5) is to deliver few current to CCD negative voltage. z COMP4 The two Step-up DC-DC converters (CH1,CH2) accept inputs from 1.5V to 5.5V and regulate a resistoradjustable output up to 17V. One 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. VQFN-24L 4x4 www.richtek.com 1 RT9903 Preliminary Typical Application Circuit 2-AA Battery 1.8V to 3.2V VBATT C1 10uF L1 4.7uH D1 SS0520 WLED (12V) C2 1uF 17 VDD 11 LX3 R1 4 LX1 9 FB3 C3 C4 VBATT 10uF 10uF 3.3V_Motor R2 300k C5 to C8 10uFx4 D2 SS0520 C9 1nF L2 4.7uH R4 10k 6 CS4 Q1 5 7 C10 4.7nF www.richtek.com 2 13 14 12 15 19 23 10 8 R6 R7 2.2k 1.2k C12 C13 R9 2.2M FB1 20 R8 2.7k C14 EN1 EN2 EN3 EN4 COMP1 COMP2 COMP3 COMP4 C17 1nF C18 10uF RT9903 LX2 24 L4 4.7uH D4 SS0520 R11 5.1M FB2 22 EXT4 FB4 +12V (+LCD) R10 200k VBATT C21 to C23 10uFx3 +15V (+CCD) C20 1nF R12 360k Si2302 Chip Enable R5 1.2k 18 C19 10uF R3 130k C11 500pF L3 4.7uH D3 SS0520 RT 21 AGND 16 PGND R15 10 C16 10uF C15 4.7uF INCD CX FB-CP 2 1 3 C24 68nF D5 SS0520 D6 SS0520 VCC 3.3V -7.5V (-CCD) R13 750k C25 to C26 10uFx2 R14 330k C27 1uF 6.8nF 56nF 4.7nF DS9903-07 August 2007 RT9903 Preliminary V_3.3V VBATT C1 10uF L1 4.7uH D1 SS0520 WLED (12V) 17 VDD 11 LX3 C2 1uF R1 C3 C4 10uF 10uF LX1 4 RT 21 AGND 16 PGND 9 FB3 R15 10 C16 10uF C15 4.7uF VBATT FB1 D2 SS0520 R2 300k C5 to C8 10uFx4 C9 1nF R4 10k 6 Q1 5 13 14 12 15 Chip Enable 19 23 10 8 C11 500pF C10 4.7nF LX2 CS4 24 R6 R7 2.2k 1.2k C12 C13 C21 to C23 10uFx3 +15V (+CCD) C20 R11 5.1M FB2 22 1nF C28 R12 360k INCD EN1 EN2 CX EN3 EN4 COMP1 COMP2 COMP3 COMP4 C18 10uF R10 200k L4 4.7uH D4 SS0520 EXT4 FB4 1nF RT9903 Si2302 7 +12V (+LCD) C17 R9 2.2M 20 C19 10uF R3 130k R5 1.2k 18 VBATT L2 4.7uH 3.3V_Motor L3 4.7uH D3 SS0520 FB-CP 2 1 C24 68nF D5 SS0520 D6 SS0520 3 VCC 3.3V R8 2.7k C14 -7.5V (-CCD) R13 750k C25 to C26 10uFx2 R14 330k C27 1uF 6.8nF 56nF 4.7nF Function Block Diagram FB1 COMP2 EN2 LX2 COMP1 EN1 LX1 CH1 V-Mode Step-Up PWM VDD CH2 V-Mode Step-Up PWM + VREF 0.2V DS9903-07 August 2007 EN3 LX3 Charge Pump + CH4 C-Mode Step-Up PWM + AGND COMP3 - INCD CX FBCP + - VREF 1V - CH3 C-Mode Step-Up PWM FB2 FB3 COMP4 EN4 EXT4 CS4 Thermal Protection + - Oscillator RT Soft Start 10uA FB4 PGND (Exposed Pad) www.richtek.com 3 RT9903 Preliminary Functional Pin Description Pin No. Pin Name Pin Function 1 CX Charge Pump External Driver Pin. 2 INCD Charge Pump Input Pin. 3 FB_CP Charge Pump Feedback Pin. 4 RT Frequency Setting Resistor Connection Pin. 5 EXT4 CH4 External Power Switch. 6 CS4 CH4 Current Sense Input Pin. 7 FB4 CH4 Feedback Input. 8 COMP4 CH4 Feedback Compensation Pin. 9 FB3 CH3 Feedback Input. 10 COMP3 CH3 Feedback Compensation Pin. 11 LX3 CH3 Switch Node. 12 EN3 CH3 Enable Input Pin. 13 EN1 CH1 Enable Input Pin. 14 EN2 CH2 Enable Input Pin. 15 EN4 CH4 Enable Input Pin. 16 PGND Power Ground. 17 VDD Power Input Pin. 18 LX1 CH1 Switch Node. 19 COMP1 CH1 Feedback Compensation Pin. 20 FB1 CH1 Feedback Input. 21 AGND Analog Ground. 22 FB2 CH2 Feedback Input. 23 COMP2 CH2 Feedback Compensation Pin. 24 LX2 CH2 Switch Node. Exposed Pad (25) GND www.richtek.com 4 The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. DS9903-07 August 2007 RT9903 Preliminary Absolute Maximum Ratings z z z z z z z z z (Note 1) 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 z z −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 (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 Symbol Test Condition Min Typ Max Units VDD Pin Voltage 2.4 -- 5.5 V VDD Pin Voltage Supply Voltage VDD Operating Voltage VVDD VDD Start-up Voltage VDD Over Voltage Protection 1.5 -- -- V VDD(OVP) VDD Pin Voltage 6 -- -- V IOFF -- 0.01 1 μA -- 200 250 μA -- 210 260 μA -- 250 300 μA -- 200 250 μA Supply Current Shutdown Supply Current VDD = 3.6V, VEN1 to 4 = 0V VVDD =3.6V, CH1 DC/DC Converter Supply Current IVDD1 VFB1 = VREF + 0.15V VEN1 = 3.3V, VEN2 = 0V, VEN3 = 0V, VEN4 = 0V VVDD = 3.6V, 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, CH3 DC/DC Converter Supply Current IVDD3 VFB3 = VREF + 0.15V VEN1 = 0V, VEN2 = 0V, VEN3 = 3.3V, VEN4 = 0V VVDD = 3.6V, CH4 DC/DC Converter Supply Current IVDD4 VFB4 = VREF + 0.15V VEN1 = 0V, VEN2 = 0V, VEN3 = 0V, VEN4 = 3.3V To be continued DS9903-07 August 2007 www.richtek.com 5 RT9903 Preliminary Parameter Symbol Test Condition Min Typ Max Units Oscillator Free Running Frequency FOSC 400 500 600 kHz CH1, CH2, CH3 Maximum Duty Cycle DMAX1,2,3 RT = Open 93 95 -- % CH4 Maximum Duty Cycle DMAX4 75 80 85 % Reference Voltage (CH1, CH2, CH3, CH4, CH5) Feedback Reference Voltage VFB1, 2, 4 CH1, CH2, CH4 0.98 1 1.02 V Feedback Reference Voltage VFB3 CH3 0.18 0.2 0.22 V Feedback Voltage (Charge Pump) VFBCP CH5 -0.02 0 0.02 V -- 200 -- μs Compensation Source Current -- 22 -- μA Compensation Sink Current -- 22 -- μA -- 0.6 -- Ω 0.7 -- -- A -- 0.6 -- Ω 0.7 -- -- A -- 0.6 -- Ω CH3 Current Limitation 0.7 -- -- A Charge Pump On Resistance of N-MOSFET 15 20 25 Ω Error Amplifier GM FB1 = COMP Power Switch CH1 On Resistance of MOSFET RDS1(ON) N-MOSFET, VDD = 3.3V CH1 Current Limitation CH2 On Resistance of MOSFET RDS2(ON) N-MOSFET, VDD = 3.3V CH2 Current Limitation CH3 On Resistance of MOSFET RDS3(ON) N-MOSFET, VDD = 3.3V Charge Pump On Resistance of P-MOSFET 15 20 25 Ω CH4 Over Current Threshold Voltage 0.3 0.4 0.5 V CH4 On Resistance of N-MOSFET 3 6 9 Ω CH4 On Resistance of P-MOSFET -- 20 -- Ω Control EN1, EN2, EN3, EN4 Input High Level Threshold VVDDM = 3.3V -- 0.8 1.3 V EN1, EN2, EN3, EN4 Input Low Level Threshold VVDDM = 3.3V 0.4 0.8 -- V ICS4 8 10 12 μA TSD -- 180 -- °C 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 is 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 RT9903 Preliminary Typical Operating Characteristics VLX1 & Output Ripple CH1 Efficiency vs. Output Current 100 VOUT = 12V LX1 (5V/Div) 90 VIN = 3.8V VIN = 4.5V 85 80 VIN = 2.5V Output Ripple (50mV/Div) Efficiency (%) 95 VIN = 3V 75 70 VBAT = 2.5V, VDD = 3.3V, @IOUT = 30mA 65 0 5 10 15 20 25 30 35 40 45 50 Time (1us/Div) Output Current (mA) LX1 (5V/Div) VLX1 & Output Ripple VBAT = 3V, VDD = 3.3V, @IOUT = 30mA Output Ripple (50mV/Div) Output Ripple (50mV/Div) LX1 (5V/Div) VLX1 & Output Ripple VBAT = 3.8V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) Time (1us/Div) CH2 Efficiency vs. Output Current VLX1 & Output Ripple 100 95 Efficiency (%) LX1 (5V/Div) Output Ripple (50mV/Div) VOUT = 15V VIN = 3.8V 90 VIN = 4.5V 85 80 VIN = 2.5V VIN = 3V 75 VBAT = 4.2V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) DS9903-07 August 2007 70 0 5 10 15 20 25 30 Output Current (mA) www.richtek.com 7 RT9903 Preliminary Output Ripple (20mV/Div) Output Ripple (20mV/Div) LX2 (5V/Div) VLX2 & Output Ripple LX2 (5V/Div) VLX2 & Output Ripple VBAT = 2.5V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) VLX2 & Output Ripple VLX2 & Output Ripple Output Ripple (20mV/Div) Output Ripple (20mV/Div) LX2 (5V/Div) LX2 (5V/Div) Time (1us/Div) VBAT = 3.8V, VDD = 3.3V, @IOUT = 30mA 100 VBAT = 4.2V, VDD = 3.3V, @IOUT = 30mA Time (1us/Div) Time (1us/Div) CH3 Efficiency vs. Input Voltage VLX3 & Output Ripple 4 series WLED, ILED = 20mA LX3 (5V/Div) 95 90 85 Output Ripple (100mV/Div) Efficiency (%) VBAT = 3V, VDD = 3.3V, @IOUT = 30mA 80 75 2 2.4 2.8 3.2 3.6 Input Voltage (V) www.richtek.com 8 4 4.4 VBAT = 2.5V, VDD = 3.3V, @IOUT = 20mA Time (1us/Div) DS9903-07 August 2007 RT9903 Preliminary LX3 (5V/Div) VLX3 & Output Ripple Output Ripple (100mV/Div) Output Ripple (100mV/Div) LX3 (5V/Div) VLX3 & Output Ripple VBAT = 3V, VDD = 3.3V, @IOUT = 20mA VBAT = 3.8V, VDD = 3.3V, @IOUT = 20mA Time (1us/Div) Time (1us/Div) CH4 Efficiency vs. Output Current VLX3 & Output Ripple LX3 (5V/Div) 100 VOUT = 3.3V Output Ripple (100mV/Div) Efficiency (%) 95 VIN = 3V 90 VIN = 2V 85 VBAT = 4.2V, VDD = 3.3V, @IOUT = 20mA VIN = 2.5V 80 Time (1us/Div) 1 10 100 1000 Output Current (mA) LX4 (2V/Div) VLX4 & Output Ripple Output Ripple (20mV/Div) Output Ripple (20mV/Div) LX4 (2V/Div) VLX4 & Output Ripple VBAT = 2V, VDD = 3.3V, @IOUT = 100mA Time (1us/Div) DS9903-07 August 2007 VBAT = 2V, VDD = 3.3V, @IOUT = 350mA Time (1us/Div) www.richtek.com 9 RT9903 Preliminary LX4 (2V/Div) VLX4 & Output Ripple Output Ripple (20mV/Div) Output Ripple (20mV/Div) LX4 (2V/Div) VLX4 & Output Ripple VBAT = 2.5V, VDD = 3.3V, @IOUT = 100mA VBAT = 2.5V, VDD = 3.3V, @IOUT = 350mA VLX4 & Output Ripple VLX4 & Output Ripple Output Ripple (20mV/Div) Output Ripple (20mV/Div) LX4 (2V/Div) Time (1us/Div) LX4 (2V/Div) Time (1us/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 100mA Time (1us/Div) CH4 Load Transient Response CH4 Load Transient Response VBAT = 2V, VDD = 3.3V, @IOUT = 100mA to 350mA Time (1ms/Div) www.richtek.com 10 Output Current (200mA/Div) Output Ripple (100mV/Div) Time (1us/Div) Output Ripple (200mV/Div) Output Current (200mA/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 350mA VBAT = 2.5V, VDD = 3.3V, @IOUT = 100mA to 350mA Time (1ms/Div) DS9903-07 August 2007 RT9903 Preliminary VCX (5V/Div) VCX & Output Ripple Output Ripple (20mV/Div) VBAT = 3V, VDD = 3.3V, @IOUT = 100mA to 350mA VBAT = 2.5V, VDD = 3.3V Time (1ms/Div) Time (2.5us/Div) VCX & Output Ripple VCX & Output Ripple Output Ripple (20mV/Div) Output Ripple (20mV/Div) VCX (5V/Div) VCX (5V/Div) Output Current (200mA/Div) Output Ripple (100mV/Div) CH4 Load Transient Response VBAT = 3V, VDD = 3.3V VBAT = 3.8V, VDD = 3.3V Time (2.5us/Div) Time (2.5us/Div) VCX & Output Ripple Frequency vs. RRT Resistor VCX (5V/Div) 2500 Output Ripple (20mV/Div) Frequency (kHz)1 2000 1500 1000 500 VBAT = 4.2V, VDD = 3.3V Time (2.5us/Div) 0 0 50 100 150 200 250 300 RRT (kΩ) DS9903-07 August 2007 www.richtek.com 11 RT9903 Preliminary Application Information 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 RCOMP and CCOMP are compensation components. www.richtek.com 12 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. 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. DS9903-07 August 2007 RT9903 Preliminary 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. 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. Over Voltage Protection 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. Current Limit Protection Current Limit 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. 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. DS9903-07 August 2007 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 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 www.richtek.com 13 RT9903 Preliminary Step-2 Calculate CC INCD Choose fC = 10KHz, and then CC is calculated from the simplified loop-gain formula. ChargePump Driver CX Negative Output Voltage CCP R1 Loop gain = Gm x 1 + SRCCC 1 ROUT VFB x x (1-D) x x SCC RCS 1+SROUTCOUT VOUT + 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. COUT 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. 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 z VF : Schottky diode forward voltage z FCP : Charge pump maximum frequency is 500kHz. The negative output voltage is set by R1 and R2. The FBCP threshold voltage is 0V. VOUT x R2 VDD x R1 www.richtek.com 14 =1 DS9903-07 August 2007 RT9903 Preliminary Outline Dimension D2 D SEE DETAIL A L 1 E E2 e b 1 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A A3 A1 Symbol 1 2 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Min Dimensions In Inches Max Min Max A 0.800 1.000 0.031 0.039 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 D2 2.300 2.750 0.091 0.108 E 3.950 4.050 0.156 0.159 E2 2.300 2.750 0.091 0.108 e L 0.500 0.350 0.020 0.450 0.014 0.018 V-Type 24L QFN 4x4 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: [email protected] DS9903-07 August 2007 www.richtek.com 15