SP7606 Wide Input Voltage Boost Controller FEATURES • Voltage-Mode PWM Operation • Adjustable Output Voltage up to 38V • Up to 85% Efficiency • Low Supply Current: • Require Tiny Inductors and Capacitors • 8-pin 2x3 DFN package • Internal Compensation • Built in current limit Demo Board Top Side Demo Board Bottom Side GENERAL DESCRIPTION The SP7606 is a fixed frequency boost controller designed to drive loads up to 38V output voltage. The SP7606 was developed to be used in conjunction with the SP7616 to drive a wide range of led chains that require high anode voltages. The ability to disconnect the output voltage feedback resistors (DD Pin) reduces shutdown current. The high switching frequency allows the use of tiny external components and saves layout space and cost. The SP7606 is packaged in a space-saving 8-pin 2x3 DFN. TYPICAL APPLICATION SCHEMATIC Boost converter 12V to 30V Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 1 of 8 SP7606 Using the Demo board. Connect the source voltage to the input pins of the demo board. The load needs to be connected to Vout pins. The SP7606 is enabled when the pin 7 (SHDN) pin is high. The demo board can deliver 400mA of output current at 30Vout from a 12V input. Design procedure for the SP7606 in DCM mode of operation. The primary mode of operation for the SP7606 is in Discontinuous Conduction mode (DCM). Below is the general procedure that was used to design the SP7606 demo board. 146-6649-01 part number. Vin 12V, 500mVp-p ripple, Vout30V, Iout 400mA. The FET requirements are a SOT-23 package for small foot print. Setting the output voltage The output voltage of the SP7606 can be set by using an output voltage divider. The internal reference of this part is set to 0.8V. Due to the internal compensation, resistor R1 might need to be chosen according to the desired gain of the compensation loop. This resistor is typically between 100K and 1M ohms. Resistor R2 can be determined by using the following equation: Vfb=800mV R1=Top Voltage divider resistor R2=Bottom Voltage divide resistor 200=the typical impedance of the DD FET R1 Chosen value of 200K R2 Value is 5.36K Calculate the on time and inductor value. Kr is a constant that sets the maximum on time to off time. A value of .8 should be used this will assure that the inductor value is chosen such that the converter runs in DCM mode. Where Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 2 of 8 SP7606 K is .8 ratio of MOSFET and diode conduction time to T (T=1/fsw) = output impedance at full load this should be multiplied by 1.5 for current limit variations Vo is the output voltage Vinmin is the minimum input voltage Ton is the maximum on time is the maximum calculated value to satisfy discontinuous mode of operation at full load. A value of 1.2 uH was chosen. The peak current is given by The calculated peak current is 4.0A Once the peak current is known for the current limit the value needs to be checked to make sure it will not trip during normal operation. Over current protection The boost regulator topology inherently does not have short circuit protection. The SP7606 converter uses a simple comparator circuit to check for an over current condition on a pulse by pulse basis. The Vset voltage threshold for the over-current (OC) pin is worst case set 0.2V. RDSON is the FET RDSON. The RDSON of the Si2318 is 0.058 ohms Vset is 0.25V Ilimit is the current limit peak current or IpDCM Ilimit is 4.31A. Since I limit is greater than IpDCM the inductor value is ok. If this value was smallerthan the calculated IpDCM then a different FET needs to be chosen with a different Rdson. Input capacitor selection For both continuous and discontinuous mode of operation the input capacitor needs to be chosen based on maximum input voltage rating and the RMS ripple current and minimum input capacitance. For DCM mode the RMS current is given by: Where K is the conduction time constant Ip is the peak inductor current calculated from equation. The RMS current is 1.65A The minimum input capacitance that is required is: Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 3 of 8 SP7606 Ton is the calculated on time Vin is the minimum input voltage The minimum amount of capacitance required is 0.34uF a value of 4.7uF was used to give good decoupling also at higher input voltage the capacitance of a ceramic capacitor can be half of the actual specified value. Calculate the Output capacitor. The minimum required output capacitor ESR is given by: The ∆Vo is the output ripple Voltage. Ip is the peak current. The minimum required value of ESR is 0.31 ohms. The minimum output capacitance required in CCM and DCM mode is approximated by Where DDCM= duty cycle fsw=switching frequency The minimum output capacitance is 1.25uF. 2 1uF capacitors were used. Duty Cycle in discontinuous conduction mode (DCM) Where fsw is the switching frequency L is the inductor Re is the effective resistance of the small signal model Re can be found by using as follows: Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 4 of 8 SP7606 Compensation When the board is operating in DCM mode of operation Type 2 compensation should be sufficient. Please refer to the SP7606 data sheet for more compensation information. Oscilloscope shots of the demo board design. Note that the oscillations observed after the current in the inductor reaches zero are normal in nearly all switching topologies and represents normal DCM operation. 400mA Load switching characteristics 12Vin 30Vout Channel 1 Vout Ripple Channel 2 LX node Channel 3 Inductor Current 2A/Div Light Load switching characteristics 12Vin 30Vout Channel 1 Vout Ripple Channel 2 LX node Channel 3 Inductor Current 2A/Div Transient Response load step Rev 00 SP7606 – Boost Controller 100mA to 400mA EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 5 of 8 SP7606 Startup characteristics into 400mA load Channel 1 Vout Channel 2 Vin BOM Reference Designator U2 C2 C6 C1 C3 C9 D38 Q1 L1 J1 R3 RGDN1 R2 R1 QTY Component Description Footprint Manufacturer 1 3 1 SP7606 1uF 50V capacitor 4.7uF 25V capacitor 4.7uF 10V capacitor 60 Volt Schottky diode 40V N FET 1.2uH Inductor 3 Pin Header 0 ohm jumper 5.36K resistor 200K resistor Test Post Demo Board PCB 2x3 DFN 0805 0805 0805 SIP SOT-23 5.2x5.8x2 Exar Murata Murata Murata Central Semi Vishay Würth Würth 1 1 1 1 2 1 1 4 1 Manufacturer Partnumber SP7606 GRM21BR71H105K GRM21BR61E475K GRM21BR61A475K CMSH2-60-SIP SI2318 7447745017 0603 0805 0805 N/A Digikey Exar 146-6649-01 Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 6 of 8 SP7606 Layout Demo Board Top Side Demo Board Bottom Side Board ordering information ORDERING INFORMATION Model Temperature Range Package Type SP7606EB........................... -40°C to +85°C.......................................................................... SP7606Evaluation Board Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 7 of 8 SP7606 Rev 00 SP7606 – Boost Controller EXAR RESERVES THE RIGHT TO MAKE CHANGES TO THIS DATASHEET. EXAR CONFIDENTIAL, PRELIMINARY & PROPRIETARY. DO NOT DISTRIBUTE OR COPY page 8 of 8