High Frequency PWM Step-Up Regulator Features General Description • • • • • The EL7512C is a high frequency, high efficiency step-up DC:DC regulator operated at fixed frequency PWM mode. With an integrated 1A MOSFET, it can deliver up to 600mA output current at up to 90% efficiency. The adjustable switching frequency is up to 1.2MHz, making it ideal for DSL applications. • • • • • 90% efficiency Up to 600mA IOUT 5V < VOUT < 18V VIN > 2V Up to 1.2MHz adjustable frequency < 3µA shutdown current Adjustable soft-start Low battery detection Internal thermal protection 1.1mm max height 10-pin MSOP package Applications • 3V to 5V, 12V, and 18V converters • 5V to 12V and 16V converters • TFT-LCD • DSL • Portable equipment • Desktop equipment EL7512C - Preliminary EL7512C - Preliminary When shut down, it draws <3µA of current. This feature, along with the minimum starting voltage of 2V, makes it suitable for portable equipment powered by one lithium ion or 3 to 4 NiMH cells. The EL7512C is available in a 10-pin MSOP package, with maximum height of 1.1mm. With proper external components, the whole converter takes less than 0.25in2 PCB space. This device is specified for operation over the full -40°C to +85°C temperature range. Typical Application Diagram Ordering Information Part No EL7512CY Package 10-Pin MSOP Tape & Reel Outline # 10µH MDP0043 VIN (2V9V) VOUT (12V up to 47µF 400mA) 10µF 100k 1 PGND LX 10 2 SGND VDD 9 3 RT 80.6kΩ FB 8 20nF SS 7 5 LBI LBO 6 10kΩ 4.7nF EL7512C Note: All information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publication; however, this data sheet cannot be a “controlled document”. Current revisions, if any, to these specifications are maintained at the factory and are available upon your request. We recommend checking the revision level before finalization of your design documentation. © 2001 Elantec Semiconductor, Inc. October 2, 2001 4 EN EL7512C - Preliminary EL7512C - Preliminary High Frequency PWM Step-Up Regulator Absolute Maximum Ratings (T A = 25°C) Values beyond absolute maximum ratings can cause the device to be prematurely damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied VIN, LBI, VDD +18V LX Voltage Storage Temperature Operating Temperature Lead Temperature 20V -65°C to +150°C -40°C to +85°C 300°C Important Note: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA Electrical Characteristics VIN = 5V, VOUT = 12V, IOUT = 0mA, F OSC = 600kHz, TA = 25°C unless otherwise specified. Parameter Description Condition IQ1 Quiescent Current - Shut-down VSHDN = 0V IQ2 Quiensent Current VSHDN = 2V, Frequency = 600kHz Min 1.31 Typ µA 2.5 4 mA 1.35 1.39 V 0.10 µA VFB Feedback Voltage Feedback Input Bias Current VIN Input Voltage Range 2 DMAX Maximum Duty Cycle 84 90 1000 1250 ILIM Current limit - Max Average Input Current Shut-down Input Bias Current VLBI LBI Threshold Voltage 190 Unit 3 IB ISHDN Max V % 1500 mA 1 µA 220 250 mV VOL-LBO LBO Output Low ILBO = 1mA 0.1 0.2 V ILEAK-LBO LBO Output Leakage Current VLBI = 250mV, VLBO = 5V 0.02 1 µA RDS-ON Switch On Resistance at 12V output 300 ILEAK-SWITCH Switch Leakage Current ∆VOUT/∆VIN Line Regulation 3V < VIN < 6V, V OUT = 12V, no load ∆VOUT/∆IOUT Load Regulation IOUT < 250µA FOSC-RANGE Frequency Range FOSC1 Switching Frequency VHI-SHDN SHDN Input High Threshold VLO-SHDN SHDN Input Low Threshold 0.5 ROSC = 100kΩ 530 670 mΩ 1 µA 0.15 %/V 1 % 1200 kHz 800 kHz 1.6 V 0.5 Pin Descriptions Pin Number Pin Name 1 PGND Power ground; connected to the source of internal N-channel power MOSFET Pin Function 2 SGND Signal ground; ground reference for all the control circuitry; needs to have only a single connection to PGND 3 RT Timing resister to adjust the oscillation frequency of the converter 4 EN Chip enable; connects to logic HI (>1.6V) for chip to function 5 LBI Low battery input; connects to a sensing voltage, or left open if function is not used 6 LBO Low battery detection output; connected to the open drain of a MOSFET; able to sink 1mA current 7 SS 8 FB 9 VDD 10 LX Soft-start; connects to a capacitor to control the start of the converter Voltage feedback input; needs to connect to resistor divider to decide V O Control circuit positive supply Inductor drive pin; connected to the drain of internal N-channel power MOSFET 2 V High Frequency PWM Step-Up Regulator Block Diagram VOUT 15µF 80.6kΩ 10kΩ VIN 4.7nF 47µF FB VDD MAX_DUTY Thermal Shut-down 10µF LX RT Reference Generator 100kΩ VREF VRAMP PWM Logic PWM Comparato 0.3Ω EN LBO 12µA LBI + + Start-up Oscillator ILOUT 7.2k 80mΩ 210mV SGND SS 20nF 3 PGND EL7512C - Preliminary EL7512C - Preliminary High Frequency PWM Step-Up Regulator Typical Performance Curves 100 Efficiency VIN=3.3V, VO=12V 100 Efficiency VIN=3.3V, VO=5V 80 Efficiency (%) Efficiency (%) 80 60 40 20 60 40 20 FS=670kHz 0 10 FS=670kHz 60 160 110 0 210 10 110 210 IO (mA) FS vs VDD 100 510 Efficiency VIN=5V, VO=12V 80 1000 RT=71.5kΩ 800 Efficiency (%) FS (kHz) 410 RT=51.1kΩ 1200 RT=100kΩ 600 RT=200kΩ 400 60 40 20 200 0 310 IO (mA) 1400 FS=670kHz 5 9 7 11 13 15 17 0 19 10 60 110 VDD (V) 210 160 Internal VREF vs TJ 360 FS vs Temperature 740 VDD=5V 1.3 720 FS (kHz) 1.25 1.2 1.15 700 VDD=10V 680 VDD=15V 1.1 1 -50 310 760 1.35 1.05 260 IO (mA) 1.4 VREF (V) EL7512C - Preliminary EL7512C - Preliminary 660 VDD=12V RT=100kΩ 0 50 100 640 -50 150 TJ (°C) 0 50 TJ (°C) 4 100 150 High Frequency PWM Step-Up Regulator Typical Performance Curves Steady State Operation (inductor continuous conduction) VIN=5V, VO=12V, IO=300mA Steady State Operation (inductor discontinuous conduction) VIN=5V, VO=12V, IO=25mA ∆VI ∆VI VLX VLX ∆VO ∆VO iL iL Power-Up VIN=5V, VO=12V, IO=300mA Load Transient Response VIN=5V, VO=12V, IO=50mA-300mA iO VIN VO ∆VO iL 5 EL7512C - Preliminary EL7512C - Preliminary EL7512C - Preliminary EL7512C - Preliminary High Frequency PWM Step-Up Regulator Applications Information Current Limit The EL7512C is a step-up regulator, operated at fixed frequency pulse-width-modulation (PWM) control. The input voltage is 2V-12V and output voltage is 5V-16V. The switching frequency (up to 1.2MHz) is decided by the resistor connected to RT pin. The MOSFET current limit is nominal 1.2A and guaranteed 1A. This restricts the maximum output current Iomax based on the following formula: ∆I L V IN I OMAX = 1 – --------× ---------2 VO Start-up After VDD reaches a threshold of about than 2V, the power MOSFET is controlled by the start-up oscillator, which generates fixed duty-ratio of 0.5-0.7 at a frequency of several hundred kilohertz. This will boost the output voltage. where: ∆IL is the inductor peak-to-peak current ripple and is decided by: V IN D ∆I L = ---------× -----L FS When VDD reaches about 3.7V, the PWM comparator takes over the control. The duty ratio will be decided by the multiple-input direct summing comparator, Max_Duty signal (about 90% duty-ratio), and the Current Limit Comparator, whichever is the smallest. D is the MOSFET turn-on radio and is decided by: V O – V IN D = ------------------------VO The soft-start is provided by the current limit comparitor. As the internal 12µA current source changes the external CSS, the peak MOSFET current is limited by the voltage on the capacitor. This in turn controls the rising rate of output voltage. The following table gives typical values: The regulator goes through the start-up sequence as well after the EN signal is pulled to HI. Maximum Output Current FS is the switching frequency. Steady-State Operation When the output reaches the preset voltage, the regulator operates at steady state. Depending on the input/output condition and component, the inductor operates at either continuous-conduction mode or discontinuous-conduction mode. In the continuous-conduction mode, the inductor current is a triangular waveform and LX voltage a pulse waveform. In the discontinuous-conduction mode, the inductor current is complete dry out before the MOSFET is turned on again. The input voltage source, the inductor, and the MOSFET and output diode parasitic capacitors forms a resonant circuit. Oscillation will occur in this period. This oscillation is normal and will not affect the regulation. VIN (V) VO (V) L (µH) FS (kHz) IOMAX (mA) 2 5 10 600 360 2 9 10 600 190 2 12 10 600 140 3 5 10 600 540 3 9 10 600 270 3 12 10 600 200 4.5 9 10 600 400 4.5 12 10 600 280 4.5 15 10 600 220 9 12 10 600 600 9 15 10 600 420 Component Considerations It is recommended that CIN is larger than 10µF. Theoretically, the input capacitor has ripple current of ∆IL. Due to high-frequency noise in the circuit, the input current ripple may exceed the theoretical value. Larger capacitor will reduce the ripple further. At very low load, the MOSFET will skip pulse sometimes. This is normal. 6 High Frequency PWM Step-Up Regulator The inductor has peak and average current decided by: rating, the output capacitor should also be able to handle the rms current is given by: ∆I L I LPK = I LAVG + --------2 I CORMS = IO I LAVG = ------------1–D 2 ∆I L 1 ( 1 – D ) × D + -------------------2- × ------ × I LAVG 12 I LAVG Layout Considerations The inductor should be chosen to be able to handle this current. Furthermore, due to the fixed internal compensation, It is recommended that maximum inductance of 10µH and 15µH to be used in the 5V and 12V or higher output voltage, respectively. The layout is very important for the converter to function properly. Power Ground ( ) and Signal Ground (---) should be separated to ensure that the high pulse current in the Power Ground never interferes with the sensitive signals connected to Signal Ground. They should only be connected at one point. The output diode has average current of IO, and peak current the same as the inductor's peak current. Schottky diode is recommended and it should be able to handle those currents. The trace connected to pin 8 (FB) is the most sensitive trace. It needs to be as short as possible and in a “quiet” place, preferably between PGND or SGND traces. Output voltage ripple is the product of peak inductor current times the ESR of output capacitor. Low ESR capacitor is to be used to reduce the output ripple. The minimum out capacitance of 330µF, 47µF, and 33µF is recommended for 5V, 12V, and 16V for 600kHz switching frequency, respectively. For 1MHz switching frequency, 220µF, 33µF, and 22µF capacitor can be used for the output voltages. In addition to the voltage In addition, the bypass capacitor connected to the VDD pin needs to be as close to the pin as possible. The heat of the chip is mainly dissipated through the PGND pins. Maximizing the copper area around these pins is preferable. In addition, a solid ground plane is always helpful for the EMI performance. The demo board is a good example of layout based on these principles. Please refer to the EL7512C Application Brief for the layout. 7 EL7512C - Preliminary EL7512C - Preliminary EL7512C - Preliminary EL7512C - Preliminary High Frequency PWM Step-Up Regulator Package Outline Drawing NOTE: The package drawing shown here may not be the most recent revision. To verify the latest version, please refer to the Elantec website at: http://www.elantec.com/pages/package_outline.html 8 EL7512C - Preliminary EL7512C - Preliminary High Frequency PWM Step-Up Regulator General Disclaimer Specifications contained in this data sheet are in effect as of the publication date shown. Elantec, Inc. reserves the right to make changes in the circuitry or specifications contained herein at any time without notice. Elantec, Inc. assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. October 2, 2001 WARNING - Life Support Policy Elantec, Inc. products are not authorized for and should not be used within Life Support Systems without the specific written consent of Elantec, Inc. Life Support systems are equipment intended to support or sustain life and whose failure to perform when properly used in accordance with instructions provided can be reasonably expected to result in significant personal injury or death. Users contemplating application of Elantec, Inc. Products in Life Support Systems are requested to contact Elantec, Inc. factory headquarters to establish suitable terms & conditions for these applications. Elantec, Inc.’s warranty is limited to replacement of defective components and does not cover injury to persons or property or other consequential damages. Elantec Semiconductor, Inc. 675 Trade Zone Blvd. Milpitas, CA 95035 Telephone: (408) 945-1323 (888) ELANTEC Fax: (408) 945-9305 European Office: 44-118-977-6020 Japan Technical Center: 81-45-682-5820 9 Printed in U.S.A.