SP6649 Sipex, SP6649 Datasheet - Page 4

• Manufacturer Part Number: SP6649
• Description: Ultra-low Quiescent Current / High Efficiency Boost DC-DC Regulator
• Manufacturer: Sipex

BLOCK DIAGRAM
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
12µA 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.
Rev:001 Date:11/20/03 SP6649 Ultra-low Quiescent Current, High Efficiency Boost DC-DC Regulator
SHDN
Rlim
LBI
FB
SDI
0.61V
Ipkset
INTERNAL
Ref
Block
Vbatt
current
control
-
+
VBATT
c
SDI
n
IBIAS
0.61V
0.61V
current
reference
+
-
1.25V
c
+
-
c
VBATT
VO
REF
FB
UVLO
Min
Toff
+
-
c
TOFF
VOLOW
S
R
Q
Qn
SP6649
CHARGE
4
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 (t
and a maximum on-time (t
t
t
K
K
OFF
ON
ON
OFF
switch
buffer
charge end
= 3.3Vµs.
K
= 1.1Vµs and
K
IUC
QKILL
ON
NMOS
OFF
QKILL
PMOS
/ V
/ (V
BATT
reference
LX
current
LX
OUT
VBATT
with
undercurrent
comparator
- V
VO
SWITCH GROUND
© Copyright 2002 Sipex Corporation
overcurrent
comparator
+
INTERNAL
SUPPLY
-
Max
Ton
c
BATT
INTERNAL
GROUND
ON
,
) and
MAX
PGND
) where:
GND
VOUT
LBON
OFF
,
LOAD
MIN
)