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| PRELIMINARY INFORMATION (R) SP6641A/6641B Ultra Low Quiescent Current, High Efficiency Boost DC-DC Regulator LX s 10A, Ultra Low Quiescent Current s Wide Input Voltage Range: 0.9V to 4.5V s 90mA IOUT at 1.3V Input, 1AA (SP6641A) s 500mA, IOUT at 2.6V Input, 2AA (SP6641B) s Fixed 3.3V or 5.0V Output Voltage s 85% Efficiency s 0.3 NFET RDSon s Only 4 External Components Required s Startup Voltage Guaranteed at 0.9V s 0.33A Inductor Current Limit (SP6641A) s 1A Inductor Current Limit (SP6641B) s Logic Shutdown Control SP6641 GND VBATT SHDN 5 Pin SOT-23 VOUT APPLICATIONS s Medical Monitors s PDA's s DSC's s MP3 Players s Pagers s Portable Handheld Devices DESCRIPTION The SP6641 is an ultra-low quiescent current, high efficiency, DC-DC boost converter designed for single and dual cell alkaline, or Li-ion battery applications found in medical monitors, PDA's, MP3 players, and other handheld portable devices. The SP6641 features a 10A quiescent current, a 0.3 N-channel charging switch, 0.9V input startup, and a 0.33A or 1.0A inductor current limiting feature. It is offered in a 5 pin SOT-23 package and provides an extremely small power supply footprint optimized for portable applications. The SP6641 is preset to 3.3V and can be controlled by a 1nA active LOW shutdown pin. TYPICAL APPLICATION DIAGRAMS 0.9V to 3.3V VIN L1 22H D1 MBR0530 3.3V, 190mA VOUT 0.9V to 3.3V VIN L1 10H D1 ZETEX ZHCS2000 3.3V, 500mA VOUT C1 22F SP6641A LX VBATT GND SHDN VOUT C1 100F C2 22F SP6641B LX VBATT GND C2 100F SHDN SHDN SHDN VOUT Rev. 8/27/01, *Patent Pending SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 1 PRELIMINARY INFORMATION ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. LX, VOUT, SHDN, VBATT to GND pin ....... -0.3 to 6.0V LX Current .......................................................... 1.5A Reverse VBATT Current ................................... 220mA Storage Temperature ........................ -65C to 150C Operating Temperature ..................... -40C to +85C Lead Temperature (Soldering, 10 sec) .......... 300 C ELECTRICAL SPECIFICATIONS VBATT = VSHDN = 1.3V, ILOAD = 0mA, -40C SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 2 PRELIMINARY INFORMATION PIN DESCRIPTION PIN NO. 1 PIN NAME LX DESCRIPTION Inductor switching node. Connect one terminal of the inductor to the positive terminal of the battery. Connect the second terminal of the inductor to this pin. The inductor charging current flows into LX, through the internal charging N-channel FET, and out through the GND pin. Ground pin. The internal regulator bias currents and the inductor charging current flows out of this pin. Output voltage sense pin, internal regulator voltage supply, and minimum off-time one shot input. Kelvin connect this pin to the positive terminal of the output capacitor. Shutdown. Tie this pin to VBATT for normal operation. Tie this pin the ground to disable all circuitry inside the chip. In shutdown mode, the output voltage will float at a diode drop below the battery potential. Battery voltage pin. The startup circuitry runs off of this pin. The regulating circuitry also uses this voltage to control the minimum offtime. TOFF KOFF / (VOUT - VIN). 2 3 GND VOUT 4 SHDN 5 VBATT BLOCK DIAGRAM VBATT VOUT VBATT LX Internal VBATT VBATT VOUT LOAD SU EN OSC VOUT VBATT R TOFF Q CHARGE NGATE M VOUT 1 DRIVER LX + SUGATE IPK/M ITH C - ICHN SHDN SHDN Min. TOFF VOUT GND REFREADY SHDN Ref Block Internal Ground + REF FB C - VOUT(LOW) Qn S VOUT SP6641 Internal Supply Rev. 8/27/01, *Patent Pending SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 3 PRELIMINARY INFORMATION OPERATION General Overview The SP6641 is a high efficiency, low quiescent current step-up DC-DC converter ideal for single and dual cell alkaline and single cell Li on battery applications such as medical monitors, PDA's, MP3 players, and other portable end products. The SP6641's 10A quiescent current, low 0.3 NFET switch, and unique PFM control scheme combine to provide excellent efficiency over a wide output power range. Other features include a logic level enable control pin, guaranteed 0.9V startup, a tiny SOT23 5 pin package, and precise inductor peak current control. SP6641A sources up to 90mA at 1.3V, typ. and SP6641B sources up to 500mA at 2.6V, typ. by supporting different peak inductor current levels. Only two capacitors, an inductor, and a diode are required to build a power supply. Loop Regulation The SP6641 combines a fixed inductor peak current limit, a feed-forward minimum off-time one-shot, and a precision loop comparator to regulate the output voltage. Under light-load conditions the loop operates as a standard PFM converter. The frequency of fixed amplitude inductor current triangles is modulated to regulate the load. Under heavy load conditions, the converter adjusts the number of successive continuous mode current pulses to regulate the load. Refer to the block diagram for the following explanation of operating modes in loop regulation. The output voltage is internally divided down and fed to the negative terminal of the loop comparator. A +1.25V bandage reference voltage is applied to the positive terminal of the comparator. As the output voltage droops below the regulation threshold due to the load the loop comparator output (signal VOUT(LOW)) transitions to a logic "1". This sets the SR latch and initiates inductor charging by pulling the signal NGATE high. Inductor charging continues until the current reaches the internally programmed limit, at which point, the off-time one-shot is triggered. The off-time one-shot via signal TOFF resets the SR latch regardless of the SET state (VOUT(LOW)), opens the NMOS charge switch, and forces the Rev. 8/27/01, *Patent Pending inductor to discharge through the rectifying diode for a minimum time defined by the oneshot duration. The end of the off-time pulse releases the SR latch, and its output state is once again determined by the output of the loop comparator (VOUT(LOW)). Under light load conditions, the output voltage will have been pulled above the regulation threshold during the minimum off-time, the signal VOUT(LOW) will be a logic "0", and the NMOS charging switch will remain open. The inductor current discharges until it reaches zero or the loop comparator triggers a new charge cycle. Under a heavy load, the output voltage will remain below the regulation point at the end of the off-time pulse. In this condition, VOUT(LOW) has a logic value of 1 which immediately starts a new charge/discharge cycle defined by the peak inductor current and the minimum offtime. The inductor current will remain in a continuous conduction mode until the loop comparator indicates the output voltage is above the regulation threshold, and the inductor current will relax towards zero. During continuous mode bursts, the inductor current frequency and ripple amplitude are controlled by the minimum off-time one-shot and the input and output voltage levels. The SP6641 sets the minimum off-time to: KOFF TOFF = (VOUT - VIN), where: KOFF VOUT VIN = Off-time Constant, typically 1.5s*V = Output Voltage = Input Voltage Plugging the TOFF expression into the boost mode equations yields the maximum output current in regulation: IOUT(MAX) ( )( VIN VOUT IPK - KOFF 2L ) where: = Efficiency, typically 0.80 to 0.90 IPK = Programmed inductor peak current, typically 0.33A for the SP6641A, typically 1.0A for the SP6641B. L = Inductor value (c) Copyright 2001 Sipex Corporation SP6641A/6641B Low Quiescent Current Boost Regulator 4 PRELIMINARY INFORMATION Loop Regulation: continued Ignoring the conduction losses of VD and VC, the burst frequency equation simplifies to: (VOUT - VIN)VIN FBURST = KOFFVOUT Startup The internal regulator circuitry is bootstrapped to the VOUT pin. This requires a low voltage oscillator and charging switch powered from the VBATT pin to pump up the output voltage until the reference is established. The reference provides a REFREADY signal that determines when output control is handed over to the regulator. REFREADY shuts down the startup circuit and enables the regulator when the reference is valid and VOUT is above +1.9V. Once the regulator is given control it will continue to pump up the output at full power until regulation is reached. For two cell alkaline input voltages and above, the output voltage will be pulled above +1.9V quickly through the rectifying diode before the reference has a chance to establish. In this scenario the startup circuit will coarsely regulate around +2.8V until the REFREADY signal asserts. This keeps the output from overshooting in startup with higher input voltages. Startup is guaranteed at +0.9V at room temperature with a 3k load. Heavier loads will require a higher input voltage. Shutdown/Enable Control Pin 4 of the device is a VBATT referred control pin that shuts down the converter with the pin tied to ground, or enables the converter with the pin tied to VBATT. When the converter is shutdown the power switch is opened and all circuit biasing is extinguished leaving only junction leakage currents on supply pins 3 and 5. The output voltage will droop to one diode drop below the battery voltage through the rectifying diode. After pin 4 is brought high, the startup circuit is enabled and starts pumping up the output until REFREADY hands over control to the internal regulator. The SP6641 feed forward off-time control delivers more load current than constant off-time control because the input battery voltage drops during its life cycle. The term (IPK - KOFF/2L) is the average current delivered to the output capacitor during the discharge phase. This is constant with respect to input and output voltage. With constant off-time control, the average discharge current term becomes (IPK-TOFF*(VOUT-VIN)/2L), which decreases as the input voltage drops. Table 1 illustrates the average inductor current delivered to the load during discharge versus the input voltage. The SP6641 feed forward offtime control and the constant off-time control are compared. For purposes of illustration, the off times of each control scheme are normalized at a typical two cell alkaline input voltage of 2.6V. The values used in Table 1 are: IPK = 0.33A L = 22H VOUT= 3.3V TOFF (SP6641) = 1.5V*s/(3.3-VIN) TOFF (constant) = 2.14s SP6641 TOFF 5.00s 2.14s 1.15s 0.75s 0.65s Avg Il 0.30A 0.30A 0.30A 0.30A 0.30A 3.0 2.6 2.0 1.3 1.0 Constant TOFF TOFF 2.14s 2.14s 2.14s 2.14s 2.14s Avg Il 0.32A 0.30A 0.27A 0.23A 0.22A VIN Table 1- Average IL vs. Input Voltage The following equation defines the burst mode frequency under heavy load conditions: F BURST = ( VOUT - VIN KOFF )( VIN - VC VOUT + VD -VC ) where: VD = Forward schottky drop, (0.4V, typ) VC = Average charging switch drop, Rnmos*IPK, typically 0.1V Rev. 8/27/01, *Patent Pending SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 5 PRELIMINARY INFORMATION PACKAGE: 5 Lead SOT23 b C L e E e1 D C L A A2 A C L a 0.20 DATUM 'A' C A1 A .10 E1 L 2 SYMBOL A A1 A2 b C D E E1 L e e1 a MIN 0.90 0.00 0.90 0.25 0.09 2.80 2.60 1.50 0.35 0.95ref 1.90ref 0 O MAX 1.45 0.15 1.30 0.50 0.20 3.10 3.00 1.75 0.55 10 O Rev. 8/27/01, *Patent Pending SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 6 PRELIMINARY INFORMATION ORDERING INFORMATION Part Number Temperature Range Package Type SP6641AEK-3.3 ....................................... -40C to 85C ......................................... 5-Pin SOT-23 SP6641AEK-3.3/TR ................................. -40C to 85C ................. (Tape & Reel) 5-Pin SOT-23 SP6641BEK-3.3 ....................................... -40C to 85C ......................................... 5-Pin SOT-23 SP6641BEK-3.3/TR ................................. -40C to 85C ................. (Tape & Reel) 5-Pin SOT-23 Corporation SIGNAL PROCESSING EXCELLENCE Sipex Corporation Headquarters and Sales Office 22 Linnell Circle Billerica, MA 01821 TEL: (978) 667-8700 FAX: (978) 670-9001 e-mail: sales@sipex.com Sales Office 233 South Hillview Drive Milpitas, CA 95035 TEL: (408) 934-7500 FAX: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Rev. 8/27/01, *Patent Pending SP6641A/6641B Low Quiescent Current Boost Regulator (c) Copyright 2001 Sipex Corporation 7 |
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