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SP6648 Datasheet, PDF (4/16 Pages) Sipex Corporation – Ultra-low Quiescent Current, High Efficiency Boost Regulator
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FUNCTIONAL DIAGRAM
VBATT
SHDN
INTERNAL
VBATT
SDI 0.61V
VBAVTTO
Min
TOFF
-
UVLO
c
+
TOFF
R
FB
RLIM
LBI
n
SDI
Ref
IBIAS
1.25V
Block
0.61V +
c
-
REF +
FB
c
-
VOLOW
S
current
control
Ipkset
-
c
0.61V
+
current
reference
LX
QKILL
charge end
IUC
Q
CHARGE
switch
buffer
QKILL
PMOS
NMOS
undercurrent
comparator
INTERNAL
SUPPLY
VO
VBATT
Max
Ton
VOUT
Qn
SP6648
LX
current
reference
+
c
-
overcurrent
comparator
SWITCH GROUND
INTERNAL
GROUND
LOAD
PGND
GND
LBON
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
12µA provides excellent efficiency, up to 94%.
In addition to the main switch, a 0.3Ω internal
MOSFET the SP6648 has an internal synchro-
nous rectifier, increasing efficiency and reduc-
ing the space of an external diode. An internal
inductive-damping switch significantly 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, thus opening both internal switches. An
externally programmable low battery detector
with open drain output provides the ability to
flag battery low condition. The inductor peak
current is externally programmable 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 = 1.0Vµs and
KON = 4.0Vµs.
Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator
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© Copyright 2004 Sipex Corporation
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