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SP6648EU-L Datasheet, PDF (4/34 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 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 = 1.0Vμs and
KON = 4.0Vμs.
Date: 6/7/06 Rev B
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator
4
© 2006 Sipex Corporation
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