SP6649 Datasheet, PDF(4/9 Page) Sipex Corporation – Ultra-low Quiescent Current, High Efficiency Boost DC-DC Regulator

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SP6649 Datasheet, PDF (4/9 Pages) Sipex Corporation – Ultra-low Quiescent Current, High Efficiency Boost DC-DC Regulator

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BLOCK DIAGRAM

VBATT

SHDN

INTERNAL

Vbatt

SDI 0.61V

VBATT

Min

Toff

UVLO

TOFF

Rlim

SDI

Ref

Block

IBIAS

1.25V

0.61V +

REF +

VOLOW

current

control

Ipkset

current

reference

LBI

0.61V

QKILL

charge end

IUC

CHARGE

switch

buffer

QKILL

PMOS

NMOS

undercurrent

comparator

INTERNAL

SUPPLY

VBATT

Max

Ton

VOUT

SP6649

current

reference

overcurrent

comparator

SWITCH GROUND

INTERNAL

GROUND

LOAD

PGND

GND

LBON

THEORY OF OPERATION

Detailed Desctiption:

The SP6649 is a step-up DC-DC converter that

starts up with input voltages as low as 0.85V

(typically) and operates with input voltages down

to 0.62V. The ultra low quiescent current of

12ÂµA provides excellent efficiencies. In addi-

tion to the 0.3 internal MOSFET the SP6649

has an internal synchronous rectifier eliminat-

ing the need for an external diode. An internal

inductive-damping switch significantly reduces

inductive ringing. If the supply voltage drops

below 0.62V the SP6649 goes into under volt-

age lock-out opening up the internal switches.

An externally programmable low battery detec-

tor with open drain output provides the user the

ability to monitor the supply voltage. The induc-

tor peak current is externally programmable to

allow for a range of inductors.

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 a higher efficiencies 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 K OFF / (VOUT - VBATT) and

tON K ON / VBATT with

KOFF = 1.1VÂµs and

KON = 3.3VÂµs.

Rev:001 Date:11/20/03 SP6649 Ultra-low Quiescent Current, High Efficiency Boost DC-DC Regulator

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