1
Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2004 Sipex Corporation
SP6648
FEATURES
Ultra-low 12A Quiescent Current
400mA Output Current at 2.6V Input: 3.3V
OUT
94% Efficiency from 2 cell to 3.3V
OUT
Wide Input Voltage Range: 0.95V to 4.5V
3.3V Fixed or Adjustable Output
Integrated Synchronous Rectifier: 0.3
0.3 Switch
Anti-Ringing Switch Technology
Programmable Inductor Peak Current
Logic Shutdown Control
Under Voltage Lock-Out at 0.61V
Programmable Low Battery Detect
Single or Dual Cell Alkaline
Small 10 pin DFN Package and Industry
Standard 10 pin MSOP
Ultra-low Quiescent Current,
High Efficiency Boost Regulator
APPLICATIONS
Camera Flash LED Driver
Wireless Mouse
PDA's
Pagers
Medical Monitors
Handheld Portable Devices
MP3 Players
DESCRIPTION
The SP6648 is an ultra-low quiescent current, high efficiency step-up DC-DC converter ideal for
single cell, dual cell alkaline and Li-Ion battery applications such as digital still cameras, PDA's,
MP3 players, and other portable devices. The SP6648 combines the high delivery associated
with PWM control, and the low quiescent current and excellent light-load efficiency of PFM control.
The SP6648 features 12A quiescent current, synchronous rectification, a 0.3 charging switch,
anti-ringing inductor switch, programmable low battery detect, under-voltage lockout and
programmable inductor peak current. The device can be controlled by a 1nA active LOW
shutdown pin.
205K
10H
3.3V
OUT
V
BATT
47F
SP6648
V
BATT
LBON
R
LIM
SHDN
FB
LX
LBI
V
OUT
P
GND
GND
47pF
47F
1F
+
10
9
8
7
6
+
LBI
SHDN
1.87K
1
2
3
4
5
LBON
124K
TYPICAL APPLICATION CIRCUIT
0
50
100
150
200
250
300
350
400
450
500
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
Vin (V)
Io (mA)
Vout=3.3V, Ipk=0.85A
Vout=5.0V, Ipk=0.85A
Maximum Load Current in Operation
SP6648
10 Pin DFN
10
9
8
7
6
1
2
3
4
5
VBATT
LBI
LBON
RLIM
SHDN
V
OUT
LX
P
GND
GND
FB
Now Available in Lead Free Packaging
2
Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2004 Sipex Corporation
LX, Vo, V
BATT
, LBON, FB to GND pin ................................ -0.3 to 6.0V
SHDN, LBI ........................................................... -0.3V to V
BATT
+1.0V
Vo, GND, LX Current ....................................................................... 2A
Reverse V
BATT
Current .............................................................. 220mA
Forward V
BATT
Current .............................................................. 500mA
Storage Temperature .................................................. -65 C to 150C
PARAMETER
MIN
TYP
MAX
UNITS
CONDITIONS
Input Voltage Operating Range, V
BATT
0.7
4.5
V
After Startup
Output Voltage Range, V
OUT
2.5
5.5
V
Start-up Input Voltage, V
BATT
0.85
1.1
V
R
LOAD
= 3k
Under Voltage Lock-out/UVLO
0.5
0.61
0.7
V
Output Voltage, V
O
3.12
3.30
3.48
V
Internal Feedback Divider
Quiescent Current into V
O
, I
QO
12
25
A
V
OUT
= 3.3V, V
FB
= 1.5V, Toggle SHDN
Quiescent Current into V
BATT
, I
QB
250
750
nA
V
OUT
= 3.3V, V
FB
= 1.5V
Shutdown Current into V
O,
I
SDO
1
500
nA
V
SHDN
= 0V
Shutdown Current into V
BATT,
I
SDB
250
750
nA
V
SHDN
= 0V, V
BATT
= 2.6V
Efficiency
84
%
V
BATT
= 1.3V, I
OUT
= 100mA, R
LIM =
2k
92
%
V
BATT
= 2.6V, I
OUT
= 200mA, R
LIM =
2k
Inductor Current Limit, I
PK
= 1600/R
LIM
650
800
1000
mA
R
LIM
= 2k
1300
1600
2000
mA
R
LIM
= 1k
100
mA
V
BATT
= 1.3V, R
LIM
= 4k
Output Current
200
mA
V
BATT
= 2.6V, R
LIM
= 4k
150
mA
V
BATT
= 1.3V, R
LIM
=2k
400
mA
V
BATT
= 2.6V, R
LIM
=2k
Minimum Off-Time Constant K
OFF
0.5
1.0
1.5
V*s
K
OFF
T
OFF
(V
OUT
- V
BATT
)
Maximum On-Time Constant K
ON
2.5
4.0
5.5
V*s
K
ON
T
ON
(V
BATT
)
Enable Valid to Output Stable
300
500
s
I
LOAD
= 1mA
NMOS
Switch Resistance
0.30
0.6
I
NMOS
= 100mA
PMOS
Switch Resistance
0.30
0.6
I
PMOS
= 100mA
FB Set Voltage, V
FB
1.19
1.25
1.31
V
External feedback
FB Input Current
1
100
nA
V
FB
=1.3V
LBI Falling Trip Voltage
0.56
0.61
0.66
V
LBI Hysteresis
25
mV
Low Output Voltage for LBON, V
OL
0.4
V
V
BATT
= 1.3V, I
SINK
= 1mA
Leakage current for LBON
1
A
V
BATT
= 1.3V, V
LBON
= 3.3V
SHDN Input Voltage, Note 1
V
IL
0.25
V
BATT
= 1.3V
V
IH
1.0
V
V
BATT
= 1.3V
V
IL
0.5
V
BATT
= 2.6V
V
IH
2.0
V
BATT
= 2.6V
SHDN Input Current
1
100
nA
LX Pin Leakage
3
A
ELECTRICAL SPECIFICATIONS
V
BATT
=V
SHDN
= 2.6V, V
FB
=0V, I
LOAD
= 0mA, T
AMB
= -40C to +85C, V
OUT
= +3.3V, typical values at 27C unless otherwise
noted. The denotes the specifications which apply over full operating temperature range -40*C to +85C, unless otherwise
specified.
Operating Temperature ................................................ -40C to +85C
Lead Temperature (Soldering, 10 sec) ....................................... 300 C
ESD Rating ........................................................................ 1.5kV HBM
These are stress ratings only and functional operation of the device at
these ratings or any other above those indicated in the operation sections
of the specifications below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect reliability.
ABSOLUTE MAXIMUM RATINGS
Note 1: SHDN must transition faster than 1V/100mS for proper operation.
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Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2004 Sipex Corporation
PIN DESCRIPTION
PIN NUMBER
PIN NAME
DESCRIPTION
1
V
BATT
Battery Voltage. The startup circuitry is powered by this pin. Battery
Voltage is used to calculate switch off time: t
OFF
= K
OFF
/ (V
OUT
-
V
BATT
). When the battery voltage drops below 0.61V the SP6648
goes into an undervoltage lockout mode (UVLO), where the part is shut
down.
2
LBI
Low Battery Input. LBI below 0.61V causes the SP6648 pin to pull
LBON pin down to ground. Use a resistor divider to program the low
voltage threshold for a specific battery configuration.
3
LBON
Low Battery Output Not. Open drain NMOS output that sinks current
to ground when LBI is below 0.61V.
4
R
LIM
Current Limit Resistor. By connecting a resistor R
LIM
from this pin to
ground the inductor peak current is set by I
PEAK
=1600/R
LIM
. The range
for R
LIM
is 9k (for 180mA) to 1.K (for 1.6A).
5
SHDN
Shutdown Not. Tie this pin high to V
BATT,
for normal operation. Pull
this pin to ground to disable all circuitry inside the chip. In shutdown
the output voltage will float down to a diode drop below the battery
voltage.
6
FB
Feedback. Connect this pin to GND for fixed +3.3V operation.
Connect this pin to a resistor voltage divider between V
OUT
and GND
for adjustable output operation.
7
GND
Ground. Connect to ground plane.
8
PGND
Power Ground. The inductor charging current flows out of this pin.
9
LX
Inductor Switching Node. Connect one terminal of the inductor to the
positive terminal of the battery. Connect the second terminal of the
inductor to this pin. The inductor charging current flows into LX,
through the internal charging N-channel FET, and out the PGND pin.
10
V
OUT
Output Voltage. The inductor current flows out of this pin during
switch off-time. It is also used as the internal regulator voltage supply.
Connect this pin to the positive terminal of the output capacitor.
4
Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2004 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
A provides excellent efficiency, up to 94%.
In addition to the main switch, a 0.3
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 (t
OFF
,
MIN
)
and a maximum on-time (t
ON
,
MAX
) where:
t
OFF
K
OFF
/ (V
OUT
- V
BATT
) and
t
ON
K
ON
/ V
BATT
with
K
OFF
= 1.0V
s and
K
ON
= 4.0V
s.
FUNCTIONAL DIAGRAM
V
BATT
SHDN
V
BATT
V
O
UVLO
0.61V
0.61V
SDI
IBIAS
V
O
SDI
INTERNAL
V
BATT
FB
LBI
R
LIM
Ipkset
current
control
current
reference
REF
FB
VO
VOLOW
S
Qn
CHARGE
Q
R
T
OFF
charge end
IUC
QKILL
LX
undercurrent
comparator
INTERNAL
SUPPLY
V
O
V
BATT
Max
Ton
V
OUT
QKILL
PMOS
NMOS
LX
current
reference
overcurrent
comparator
SWITCH GROUND
P
GND
GND
LBON
INTERNAL
GROUND
LOAD
Ref
Block
Min
T
OFF
switch
buffer
+
-
c
+
-
c
n
0.61V
SP6648
+
-
c
+
-
c
+
-
c
1.25V
+
-
c
5
Date: 7/19/04
SP6648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2004 Sipex Corporation
At light loads (as shown in plot A in Figure 1)
the charge cycle will last the maximum value for
t
ON
: For a 1V battery this would be as follows:
t
ON
= K
ON
/ V
BATT
= 4.0V
s / 1V = 4.0s
The current built up in the coil during the charge
cycle gets fully discharged (discontinuous con-
duction mode DCM) When the current in the
coil has reached zero the synchronous rectifier
switch is opened and the voltage across the coil
(from V
BATT
to LX) is shorted internally to
eliminate inductive ringing.
With increasing load (as shown in plot B in
Figure 1) this inductor damping time becomes
shorter, because the output will quickly drop
below its regulation point due to heavier load. If
the load current increases further the SP6648
enters continuous conduction mode (CCM)
where there is always current flowing in the
inductor. The charge time remains at maximum
t
ON
as long as the inductor peak current limit is
not reached as shown in plot C in Figure 1. The
inductor peak current limit can be programmed
by tying a resistor R
LIM
from the R
LIM
pin to
ground where:
I
PEAK
= 1600 / R
LIM
When the peak current limit is reached the
charge time is short-cycled.
In plot D of Figure 1, the switch current reaches
the peak current limit during the charge period
which ends the charge cycle and starts the dis-
charge cycle. However, full load is not yet
achieved because at the end of the minimum
discharge time the output was still within regu-
lation.
Maximum load is reached when this discharge
time has shrunk to the minimum allowed value
T
OFF
as shown in Plot E of Figure 1.
Inductor Current vs. Load
Ton Max.
Toff Min.
E. Iripple=Toff* (Vo
- Vi)/L
llim
llim
llim
llim
llim
Ton Max.
Ton Max.
Ton Max.
Ton Max.
Toff Min.
Toff Min.
Toff Min.
Toff Min.
D. Toff*= (Vo
- Vi)/L<Iripple<Ton*Vi/L
C. Iripple=Ton*Vi/L
B. Iripple=Ton*Vi/L
A. Iripple=Ton*Vi/L
E
D
C
B
A
Figure 1. Inductor Current vs. Load
THEORY OF OPERATION: Continued
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