LT3463/LT3463A
Dual Micropower
DC/DC Converters
with Schottky Diodes
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
Generates Well-Regulated Positive and
Negative Outputs
Low Quiescent Current:
20
µ
A (per Converter) in Active Mode
<1
µ
A in Shutdown Mode
Internal 42V Power Switches
Internal 42V Schottky Diodes
Low V
CESAT
Switch: 180mV at 150mA
Input Voltage Range: 2.4V to 15V
High Output Voltages: Up to
±40V
Low Profile (0.8mm) 3mm x 3mm DFN Package
APPLICATIO S
s
s
s
s
CCD Bias
LCD Bias
Handheld Computers
Digital Cameras
The LT
®
3463/LT3463A are dual micropower DC/DC con-
verters with internal Schottky diodes in a 10-lead 3mm
×
3mm DFN package. Negative and positive LT3463 con-
verters have a 250mA current limit. The LT3463A positive
converter also has a 250mA limit, while the negative
converter has a 400mA limit. Both devices have an input
voltage range of 2.4V to 15V, making them ideal for a wide
variety of applications. Each converter features a quies-
cent current of only 20µA, which drops to under 1µA in
shutdown. A current limited, fixed off-time control scheme
conserves operating current, resulting in high efficiency
over a broad range of load current. The 42V switch enables
high voltage outputs up to
±40V
to be easily generated
without the use of costly transformers. The low 300ns off-
time permits the use of tiny, low profile inductors and
capacitors to minimize footprint and cost in space-con-
scious portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V
IN
2.7V
TO 5V
4.7µF
V
IN
SHDN1
LT3463A
SHDN2
GND
SW2
SW1 V
OUT1
FB1
V
REF
FB2
D2
10µH
CCD Bias Supply (15V, –8V)
V
OUT1
15V
10mA
2.2µF
EFFICIENCY (%)
Efficiency and Power Loss
80
15V EFFICIENCY
75
70
65
60
15V LOSS
55
40
–8V LOSS
0
100
3463 TA01b
1M
90.9k
154k
10µH
1µF
1M
10pF
V
OUT2
–8V
50mA
3463 TA01a
50
0.1
1
10
LOAD CURRENT (mA)
4.7µF
U
V
IN
= 3.6V
240
200
POWER LOSS (mW)
U
U
–8V EFFICIENCY
160
120
80
3463f
1
LT3463/LT3463A
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT1
SW1
V
IN
SW2
D2
1
2
3
4
5
11
10 FB1
9 SHDN1
8 SHDN2
7 V
REF
6 FB2
V
IN
, SHDN1, SHDN2 Voltage ................................... 15V
SW1, SW2, V
OUT1
Voltage ....................................... 42V
D2 Voltage ............................................................. –42V
FB1, FB2 Voltage Range .............................. –0.3V to 2V
Junction Temperature ........................................... 125°C
Operating Ambient Temperature Range
(Note 2) .............................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
ORDER PART
NUMBER
LT3463EDD
LT3463AEDD
DD PART MARKING
LAFC
LBJK
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS GND
AND MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 2.5V, V
SHDN
= 2.5V unless otherwise noted.
PARAMETER
Minimum Input Voltage
Total Quiescent Current
Shutdown Current
V
REF
Pin Voltage
V
REF
Pin Voltage Line Regulation
FB1 Comparator Trip Voltage
FB1 Comparator Hysteresis
FB1 Line Regulation
FB1 Pin Bias Current (Note 3)
FB2 Comparator Trip Voltage
FB2 Comparator Hysteresis
FB2 Line Regulation (V
REF
– V
FB2
)
FB2 Pin Bias Current (Note 4)
SW1 Switch Off Time
SW2 Switch Off Time
Switch V
CESAT
(SW1, SW2)
Switch Current Limit (SW1)
Switch Current Limit (SW2)
Swith Leakage Current (SW1, SW2)
Schottky Forward Voltage (V
OUT1
, D2)
Schottky Reverse Leakage Current
SHDN1 Pin Current
SHDN2 Pin Current
SHDN1/SHDN2 Start-Up Threshold
CONDITIONS
For Both Switchers, Not Switching
V
SHDN1
= V
SHDN2
= 0V
With 124kΩ to GND
With 124kΩ to GND
High to Low Transition
2.5V < V
IN
< 15V
V
FB1
= 1.3V
Low to High Transition
2.5V < V
IN
< 15V
V
FB2
= –0.1V
V
OUT1
– V
IN
= 4V
V
OUT1
– V
IN
= 0V
V
FB2
< 0.1V
V
FB2
= 1V
I
SW
= 150mA
LT3463
LT3463A
Switch Off, V
SW
= 42V
I
D
= 150mA
V
OUT1
– V
SW
= 42V
V
D2
= –42V
V
SHDN1
= 2.5V
V
SHDN2
= 2.5V
MIN
TYP
2.2
40
0.1
1.25
0.05
1.25
8
0.05
20
3
8
0.05
20
300
1.5
300
1.5
180
250
250
400
0.01
750
1
1
4
4
1
MAX
2.4
60
1
1.27
0.10
1.275
0.10
50
12
0.10
50
UNITS
V
µA
µA
V
%/V
V
mV
%/V
nA
mV
mV
%/V
nA
ns
µs
ns
µs
mV
mA
mA
mA
µA
mV
µA
µA
µA
µA
V
ELECTRICAL CHARACTERISTICS
q
q
1.23
1.225
q
q
0
q
180
180
320
320
320
460
1
5
5
10
10
1.5
0.3
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT3463/LT3463A are guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the –40°C to 85°C
operating ambient temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 3:
Bias current flows into the FB1 pin.
Note 4:
Bias current flows out of the FB2 pin.
3463f
2
U
W
U
U
W W
W
LT3463/LT3463A
TYPICAL PERFOR A CE CHARACTERISTICS
V
CESAT
and V
DIODE
Voltage
900
800
V
CESAT
AND V
DIODE
VOLTAGE (V)
700
600
500
400
300
200
100
I
SWITCH
= 150mA
0
25
50
75
100
125
FOR BOTH SWITCHERS
I
DIODE
= 150mA
V
REF
AND V
FB1
VOLTAGE (V)
1.25
V
FB1
V
REF
V
FB2
VOLTAGE (mV)
0
–50 –25
TEMPERATURE (°C)
3463 G01
Switch Off Time
400
350
450
400
SWITCH CURRENT LIMIT (mA)
SWITCH OFF TIME (ns)
300
250
200
150
100
50
0
–50 –25
0
25
50
75
100
125
300
250
200
150
100
50
0
–50 –25
0
25
50
75
100
125
LT3463 SW1, SW2
LT3463A SW1
QUIESCENT CURRENT (µA)
TEMPERATURE (°C)
3463 G04
PI FU CTIO S
V
OUT1
(Pin 1):
Output Voltage Switcher 1. This is the
cathode of an internal Schottky diode whose anode is
connected to the SW1 pin.
SW1 (Pin 2):
Switch Pin for Switcher 1. This is the
collector of the internal NPN switch. Minimize the metal
trace area connected to this pin to minimize EMI.
V
IN
(Pin 3):
Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
SW2 (Pin 4):
Switch Pin for Switcher 2. This is the
collector of the internal NPN switch. Minimize the metal
trace area connected to this pin to minimize EMI.
D2 (Pin 5):
Diode for Switcher 2. This is the anode of an
internal Schottky diode whose cathode connected to the
GND pin.
FB2 (Pin 6):
Feedback Pin for Switcher 2. Set the output
voltage by selecting values for R3 and R4.
V
REF
(Pin 7):
Voltage Reference Pin (1.25V). This pin is
used along with FB2 to set the negative output voltage for
Switcher 2.
SHDN2 (Pin 8):
Shutdown Pin for Switcher 2. Pull this pin
above 1.5V to enable Switcher 2. Pull below 0.3V to turn
it off. Do not leave this pin floating.
3463f
U W
V
REF
and V
FB1
Voltage
1.27
10
V
FB2
Voltage
1.26
8
6
1.24
4
1.23
2
1.22
–50 –25
0
25
50
75
100
125
0
–50 –25
TEMPERATURE (°C)
3463 G02
50
25
75
0
TEMPERATURE (°C)
100
125
3463 G03
Switch Current Limit
60
Quiescent Current
LT3463A SW2
350
50
40
30
20
10
NOT SWITCHING
V
FB1
= 1.3V
V
FB2
= –0.1V
50
25
75
0
TEMPERATURE (°C)
100
125
0
–50 –25
TEMPERATURE (°C)
3463 G05
3463 G06
U
U
U
3
LT3463/LT3463A
PI FU CTIO S
SHDN1 (Pin 9):
Shutdown Pin for Switcher 1. Pull this pin
above 1.5V to enable Switcher 1. Pull below 0.3V to turn
it off. Do not leave this pin floating.
FB1 (Pin 10):
Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
GND (Pin 11):
Exposed Pad. Solder this exposed pad
directly to the local ground plane. This pad must be
electrically connected for proper operation.
BLOCK DIAGRA
V
IN
C1
3
V
IN
SHDN1
9
SHDN1
V
OUT1
R2
10
R1
1.25V
FB1
–
+
A1
SWITCHER 1
A2
LT3463: R
S1
= R
S2
= 0.1Ω
LT3463A: R
S1
= 0.1Ω, R
S2
= 0.063Ω
OPERATIO
The LT3463 uses a constant off-time control scheme to
provide high efficiency over a wide range of output cur-
rent. Operation can be best understood by referring to the
block diagram in Figure 1. When the voltage at the FB1 pin
is slightly above 1.25V, comparator A1 disables most of
the internal circuitry. Output current is then provided by
capacitor C2, which slowly discharges until the voltage at
the FB1 pin goes below the hysteresis point of A1 (typical
hysteresis at the FB1 pin is 8mV). A1 then enables the
internal circuitry, turns on power switch Q1, and the
4
W
U
U
U
U
L1
V
OUT1
V
OUT2
D3
C4
L2
V
IN
C2
C3
2
SW1
1
V
OUT1
D1
5
D2
D2
4
SW2
SHDN2 8
SHDN2
300ns
ONE-SHOT
Q1
Q2
300ns
ONE-SHOT
1.25V
V
REF
7
R3
+
R
S1
R
S2
25mV
+
25mV
+
–
FB2
6
R4
–
–
A4
SWITCHER 2
A3
V
OUT2
GND
11
3463 F01
Figure 1. Block Diagram
current in inductor L1 begins ramping up. Once the switch
current reaches 250mA, comparator A2 resets the one-
shot, which turns off Q1 for 300ns. Q1 turns on again and
the inductor currents ramp back up to 250mA, then A2
again resets the one-shot. This switching action continues
until the output voltage is charged up (until the FB1 pin
reaches 1.25V), then A1 turns off the internal circuitry and
the cycle repeats. The second switching regulator is an
inverting converter (which generates a negative output)
but the basic operation is the same.
3463f
LT3463/LT3463A
APPLICATIO S I FOR ATIO
Choosing an Inductor
Several recommended inductors that work well with the
LT3463 are listed in Table 1, although there are many other
manufacturers and devices that can be used. Consult each
manufacturer for more detailed information and for their
entire selection of related parts. Many different sizes and
shapes are available. Use the equations and recommenda-
tions in the next few sections to find the correct inductance
value for your design.
Table 1. Recommended Inductors
PART
CMD4D06
MAX
MAX HEIGHT
L (
µ
H) I
DC
(mA) DCR(
Ω
) (mm) MANUFACTURER
4.7
750
0.22
0.8
Sumida
10
500
0.46
(847) 956-0666
22
310
1.07
www.sumida.com
10
500
0.19
1.8
Sumida
22
310
0.36
4.7
600
0.16
1.2
Coilcraft
10
400
0.30
(847) 639-6400
22
280
0.64
www.coilcraft.com
10
450
0.39
1.8
Murata
15
300
0.75
(714) 852-2001
22
250
0.92
www.murata.com
4.7
340
0.85
1.8
Murata
CDRH3D16
LPO4812
LQH32C
LQH31C
Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for a boost regulator using the LT3463 (or
at least provides a good starting point). This value pro-
vides a good tradeoff in inductor size and system perfor-
mance. Pick a standard inductor close to this value. A
larger value can be used to slightly increase the available
output current, but limit it to around twice the value
calculated below, as too large of an inductance will in-
crease the output voltage ripple without providing much
additional output current. A smaller value can be used
(especially for systems with output voltages greater than
12V) to give a smaller physical size. Inductance can be
calculated as:
L
=
V
OUT
−
V
IN
(
MIN
)
+
V
D
I
LIM
t
OFF
where V
D
= 0.5V (Schottky diode voltage), I
LIM
= 250mA
(or 400mA) and t
OFF
= 300ns; for designs with varying V
IN
U
such as battery powered applications, use the minimum
V
IN
value in the above equation. For most regulators with
output voltages below 7V, a 4.7µH inductor is the best
choice, even though the equation above might specify a
smaller value.
For higher output voltages, the formula above will give
large inductance values. For a 3V to 20V converter (typical
LCD Bias application), a 21µH inductor is called for with
the above equation, but a 10µH inductor could be used
without much reduction in the maximum output current.
Inductor Selection—Inverting Regulator
The formula below calculates the appropriate inductor
value to be used for an inverting regulator using the
LT3463 (or at least provides a good starting point). This
value provides a good tradeoff in inductor size and system
performance. Pick a standard inductor close to this value
(both inductors should be the same value). A larger value
can be used to slightly increase the available output
current, but limit it to around twice the value calculated
below, as too large of an inductance will increase the
output voltage ripple without providing much additional
output current. A smaller value can be used (especially for
systems with output voltages greater than 12V) to give a
smaller physical size. Inductance can be calculated as:
W
U
U
V
OUT
+
V
D
L
=
2
I
LIM
t
OFF
where V
D
= 0.5V (Schottky diode voltage), I
LIM
= 250mA
(or 400mA) and t
OFF
= 300ns.
For higher output voltages, the formula above will give
large inductance values. For a 3V to 20V converter (typical
LCD bias application), a 49µH inductor is called for with
the above equation, but a 10µH or 22µH inductor could be
used without much reduction in the maximum output
current.
Inductor Selection—Inverting Charge Pump Regulator
For the inverting regulator, the voltage seen by the internal
power switch is equal to the sum of the absolute value of
the input and output voltages, so that generating high
3463f
5
