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SP6648ER/TR Datasheet(PDF) 4 Page - Sipex Corporation |
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SP6648ER/TR Datasheet(HTML) 4 Page - Sipex Corporation |
4 / 16 page 4 Date: 6/7/06 Rev B SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator © 2006 Sipex Corporation THEORY OF OPERATION Detailed Description The SP6648 is a step-up DC-DC converter that can start up with input voltages as low as 0.85V (typically) and operates with an input voltage down to 0.61V. Ultra low quiescent current of 12 μA provides excellent efficiency, up to 94%. In addition to the main switch, a 0.3 Ω internal MOSFET the SP6648 has an internal synchro- nous rectifier, increasing efficiency and reduc- ing the space requirements of an external diode. An internal inductive-damping switch signifi- cantly reduces inductive ringing for low-noise, high efficiency operation. If the supply voltage drops below 0.61V the SP6648 goes into under voltage lock-out mode, thus opening both inter- nal switches. An externally programmable low battery detector with open drain output provides the ability to flag a battery-low condition. The inductor peak current is externally program- mable to allow for a range of inductor values. Control Scheme A minimum off-time, current limited pulse fre- quency modulation (PFM) control scheme com- bines the high output power and efficiency of a pulse width modulation (PWM) device with the ultra low quiescent current of the traditional PFM. At low to moderate output loads, the PFM control provides higher efficiency than tradi- tional PWM converters are capable of deliver- ing. At these loads, the switching frequency is determined by a minimum off-time (tOFF, MIN) and a maximum on-time (tON, MAX) where: tOFF ≥ KOFF / (VOUT - VBATT) and tON ≤ KON / VBATT with KOFF = 1.0V μs and KON = 4.0V μs. FUNCTIONAL DIAGRAM VBATT SHDN VBATT VO UVLO 0.61V 0.61V SDI IBIAS SDI INTERNAL VBATT FB LBI RLIM Ipkset current control current reference REF FB VOLOW SQn CHARGE Q R TOFF charge end IUC QKILL LX undercurrent comparator INTERNAL SUPPLY VO VBATT Max Ton VOUT QKILL PMOS NMOS LX current reference overcurrent comparator SWITCH GROUND PGND GND LBON INTERNAL GROUND LOAD Ref Block Min TOFF switch buffer + - c + - c n 0.61V SP6648 + - c + - c + - c 1.25V |
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