Linear LT3463A Dual micropower dc/dc converters with schottky diode Datasheet

LT3463/LT3463A
Dual Micropower
DC/DC Converters
with Schottky Diodes
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FEATURES
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DESCRIPTIO
The LT®3463/LT3463A are dual micropower DC/DC converters with internal Schottky diodes in a 10-lead 3mm ×
3mm DFN package. Negative and positive LT3463 converters 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 quiescent 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 offtime permits the use of tiny, low profile inductors and
capacitors to minimize footprint and cost in space-conscious portable applications.
Generates Well-Regulated Positive and
Negative Outputs
Low Quiescent Current:
20µA (per Converter) in Active Mode
<1µA in Shutdown Mode
Internal 42V Power Switches
Internal 42V Schottky Diodes
Low VCESAT 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
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APPLICATIO S
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CCD Bias
LCD Bias
Handheld Computers
Digital Cameras
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
CCD Bias Supply (15V, –8V)
Efficiency and Power Loss
10µH
VIN
2.7V
TO 5V
1M
SW1 VOUT1
SHDN2
GND
90.9k
VREF
FB2
SW2
15V EFFICIENCY
200
2.2µF
FB1
LT3463A
154k
70
160
–8V EFFICIENCY
65
120
60
80
D2
15V LOSS
55
10µH
1µF
240
POWER LOSS (mW)
VIN
SHDN1
VIN = 3.6V
75
EFFICIENCY (%)
4.7µF
80
VOUT1
15V
10mA
1M
4.7µF
40
–8V LOSS
10pF
VOUT2
–8V
50mA
50
0.1
1
10
LOAD CURRENT (mA)
0
100
3463 TA01b
3463 TA01a
3463f
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LT3463/LT3463A
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN, SHDN1, SHDN2 Voltage ................................... 15V
SW1, SW2, VOUT1 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
TOP VIEW
ORDER PART
NUMBER
10 FB1
VOUT1
1
SW1
2
VIN
3
SW2
4
7 VREF
D2
5
6 FB2
9 SHDN1
11
8 SHDN2
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W
EXPOSED PAD (PIN 11) IS GND
AND MUST BE SOLDERED TO PCB
LT3463EDD
LT3463AEDD
DD PART MARKING
LAFC
LBJK
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 2.5V, VSHDN = 2.5V unless otherwise noted.
PARAMETER
Minimum Input Voltage
Total Quiescent Current
Shutdown Current
VREF Pin Voltage
VREF 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 (VREF – VFB2)
FB2 Pin Bias Current (Note 4)
SW1 Switch Off Time
SW2 Switch Off Time
Switch VCESAT (SW1, SW2)
Switch Current Limit (SW1)
Switch Current Limit (SW2)
Swith Leakage Current (SW1, SW2)
Schottky Forward Voltage (VOUT1, D2)
Schottky Reverse Leakage Current
SHDN1 Pin Current
SHDN2 Pin Current
SHDN1/SHDN2 Start-Up Threshold
CONDITIONS
MIN
For Both Switchers, Not Switching
VSHDN1 = VSHDN2 = 0V
With 124kΩ to GND
With 124kΩ to GND
High to Low Transition
●
1.23
●
1.225
2.5V < VIN < 15V
VFB1 = 1.3V
Low to High Transition
●
2.5V < VIN < 15V
VFB2 = –0.1V
VOUT1 – VIN = 4V
VOUT1 – VIN = 0V
VFB2 < 0.1V
VFB2 = 1V
ISW = 150mA
LT3463
LT3463A
Switch Off, VSW = 42V
ID = 150mA
VOUT1 – VSW = 42V
VD2 = –42V
VSHDN1 = 2.5V
VSHDN2 = 2.5V
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
●
0
●
180
180
320
0.3
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
320
320
460
1
5
5
10
10
1.5
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
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.
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LT3463/LT3463A
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TYPICAL PERFOR A CE CHARACTERISTICS
VCESAT and VDIODE Voltage
900
VREF and VFB1 Voltage
FOR BOTH SWITCHERS
VFB2 Voltage
1.27
10
1.26
8
600
VREF
1.25
500
400
VFB1
1.24
300
200
6
4
2
1.23
ISWITCH = 150mA
0
–50 –25
0
25
50
75
100
1.22
–50 –25
125
TEMPERATURE (°C)
0
25
50
75
100
TEMPERATURE (°C)
Switch Off Time
450
350
400
SWITCH CURRENT LIMIT (mA)
400
250
200
150
100
50
60
50
LT3463A SW2
300
250
LT3463 SW1, SW2
LT3463A SW1
150
100
25
50
75
100
125
TEMPERATURE (°C)
0
–50 –25
40
30
20
10
50
0
125
Quiescent Current
350
200
100
3463 G03
Switch Current Limit
300
50
25
75
0
TEMPERATURE (°C)
3463 G02
3463 G01
0
–50 –25
0
–50 –25
125
QUIESCENT CURRENT (µA)
100
SWITCH OFF TIME (ns)
VFB2 VOLTAGE (mV)
IDIODE = 150mA
700
VREF AND VFB1 VOLTAGE (V)
VCESAT AND VDIODE VOLTAGE (V)
800
0
25
50
75
100
125
TEMPERATURE (°C)
3463 G04
3463 G05
NOT SWITCHING
VFB1 = 1.3V
VFB2 = –0.1V
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3463 G06
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PI FU CTIO S
VOUT1 (Pin 1): Output Voltage Switcher 1. This is the
cathode of an internal Schottky diode whose anode is
connected to the SW1 pin.
D2 (Pin 5): Diode for Switcher 2. This is the anode of an
internal Schottky diode whose cathode connected to the
GND 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.
FB2 (Pin 6): Feedback Pin for Switcher 2. Set the output
voltage by selecting values for R3 and R4.
VIN (Pin 3): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
VREF (Pin 7): Voltage Reference Pin (1.25V). This pin is
used along with FB2 to set the negative output voltage for
Switcher 2.
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.
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.
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LT3463/LT3463A
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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.
GND (Pin 11): Exposed Pad. Solder this exposed pad
directly to the local ground plane. This pad must be
electrically connected for proper operation.
FB1 (Pin 10): Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
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BLOCK DIAGRA
VOUT1
L1
VOUT2
C4
D3
L2
VIN
VIN
C2
C1
3
2
VIN
9
SHDN1
C3
1
5
VOUT1
SW1
300ns
ONE-SHOT
VOUT1
SW2
D2
D1
SHDN1
4
D2
SHDN2 8
300ns
ONE-SHOT
Q2
Q1
1.25V
VREF
SHDN2
7
R3
R2
10
FB1
RS1
1.25V
+
A1
A2
–
+
+
+
–
R1
FB2
6
R4
RS2
25mV
25mV
SWITCHER 1
–
A4
A3
–
VOUT2
SWITCHER 2
GND
11
3463 F01
LT3463: RS1 = RS2 = 0.1Ω
LT3463A: RS1 = 0.1Ω, RS2 = 0.063Ω
Figure 1. Block Diagram
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OPERATIO
The LT3463 uses a constant off-time control scheme to
provide high efficiency over a wide range of output current. 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
current in inductor L1 begins ramping up. Once the switch
current reaches 250mA, comparator A2 resets the oneshot, 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.
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LT3463/LT3463A
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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 recommendations in the next few sections to find the correct inductance
value for your design.
Table 1. Recommended Inductors
PART
CMD4D06
CDRH3D16
LPO4812
LQH32C
LQH31C
MAX
MAX HEIGHT
L (µH) IDC (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
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 provides a good tradeoff in inductor size and system performance. 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 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:
L=
VOUT − VIN(MIN) + VD
ILIM
tOFF
where VD = 0.5V (Schottky diode voltage), ILIM = 250mA
(or 400mA) and tOFF = 300ns; for designs with varying VIN
such as battery powered applications, use the minimum
VIN 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:
 VOUT + VD
L = 2

ILIM


 tOFF


where VD = 0.5V (Schottky diode voltage), ILIM = 250mA
(or 400mA) and tOFF = 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
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LT3463/LT3463A
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APPLICATIO S I FOR ATIO
output voltages from a high input voltage source will often
exceed the 50V maximum switch rating. For instance, a
12V to – 40V converter using the inverting topology would
generate 52V on the SW pin, exceeding its maximum
rating. For this application, an inverting charge pump is
the best topology.
The formula below calculates the approximate inductor
value to be used for an inverting charge pump regulator
using the LT3463. As for the boost inductor selection, a
larger or smaller value can be used. For designs with
varying VIN such as battery powered applications, use the
minimum VIN value in the equation below.
L=
VOUT − VIN(MIN) + VD
ILIM
The small size and low ESR of ceramic capacitors makes
them ideal for LT3463 applications. Use only X5R and X7R
types because they retain their capacitance over wider
voltage and temperature ranges than other ceramic types.
A 1µF input capacitor and a 0.22µF or 0.47µF output
capacitor are sufficient for most applications. Table 2
shows a list of several ceramic capacitor manufacturers.
Consult the manufacturers for more detailed information
on their entire selection of ceramic capacitors. For applications needing very low output voltage ripple, larger
output capacitor values can be used.
Table 2. Recommended Ceramic Capacitor Manufacturers
AVX
PHONE
While the internal diode is designed to handle such events,
the inrush current should not be allowed to exceed 1 amp.
For circuits that use output capacitor values within the
recommended range and have input voltages of less than
5V, inrush current remains low, posing no hazard to the
device. In cases where there are large steps at VIN and/or
a large capacitor is used at the outputs, inrush current
should be measured to ensure safe operation.
Setting the Output Voltages
The output voltages are programmed using two feedback
resistors. As shown in Figure 1, resistors R1 and R2
program the positive output voltage (for Switcher 1), and
resistors R3 and R4 program the negative output voltage
(for Switcher 2) according to the following formulas:
tOFF
Capacitor Selection
MANUFACTURER
inrush current include a larger more abrupt voltage step at
VIN, a larger output capacitor tied to the outputs, and an
inductor with a low saturation current.
URL
843-448-9411
www.avxcorp.com
Kemet
408-986-0424
www.kemet.com
Murata
814-237-1431
www.murata.com
Taiyo Yuden
408-573-4150
www.t-yuden.com
Inrush Current
When VIN is increased from ground to operating voltage
while the output capacitor is discharged, an inrush current
will flow through the inductor and integrated Schottky
diode into the output capacitor. Conditions that increase
 R2
VOUT 1 = 1.25V 1 + 
 R1
 R4 
VOUT 2 = –1.25V 
 R3 
R1 and R3 are typically 1% resistors with values in the
range of 50k to 250k.
Board Layout Considerations
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To maximize efficiency, switch rise and fall times are made
as short as possible. To prevent electromagnetic interference (EMI) problems, proper layout of the high frequency
switching path is essential. The voltage signal of the SW
pin has sharp rising and falling edges. Minimize the length
and area of all traces connected to the SW pin and always
use a ground plane under the switching regulator to
minimize interplane coupling. In addition, the ground
connection for the feedback resistor R1 should be tied
directly to the GND pin and not shared with any other
component, ensuring a clean, noise-free connection.
3463f
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LT3463/LT3463A
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TYPICAL APPLICATIO
Dual Output ±20V Converter
VIN
2.7V
TO 5V
L1
10µH
C1
1µF
3
2
9
SHDN1
FB1
LT3463
8
SHDN2
GND
R2
1M
1
SW1 VOUT1
VIN
VREF
FB2
SW2
D2
4
5
11
C4
0.1µF
L2
10µH
VOUT1
20V
9mA
R1
66.5k
10
C2
0.47µF
7
6
R3
61.9k
R4
1M
D1
VOUT2
–20V
9mA
C3
0.47µF
3463 TA02
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PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.25 ± 0.05
0.200 REF
0.50
BSC
2.38 ±0.05
(2 SIDES)
1
0.75 ±0.05
0.00 – 0.05
0.25 ± 0.05
0.50 BSC
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3463f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
7
LT3463/LT3463A
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TYPICAL APPLICATIO
CCD Bias Supply
VIN
2.7V
TO 5V
L1
10µH
C1
4.7µF
3
VIN
9
2
FB1
LT3463A
8
SHDN2
GND
11
R2
1M
1
SW1 VOUT1
SHDN1
VREF
FB2
SW2
10
R1
90.9k
C2
2.2µF
7
6
R3
154k
D2
4
L2
10µH
VOUT1
15V
10mA
5
C4
1µF
D1
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN EMK316BJ225ML
C3: TAIYO YUDEN LMK316BJ475ML
C4: TAIYO YUDEN EMK212BJ105MG
C5: AVX 06035A100KAT2A
D1: DIODES, INC B0540W
L1, L2: MURATA LQH32CN100K53
Typical Waveforms for 15V Output
C5
10pF
R4
1M
C3
4.7µF
VOUT2
–8V
50mA
3463 TA01a
Typical Waveforms for –8V Output
VSW2
5V/DIV
VSW1
10V/DIV
VOUT1
AC-COUPLED
50mV/DIV
VOUT2
AC-COUPLED
50mV/DIV
IL1
200mA/DIV
IL2
200mA/DIV
2µs/DIV
3463 TA04
2µs/DIV
3463 TA05
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PART NUMBER
DESCRIPTION
COMMENTS
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Dual Output, Pos/Neg, 350mA (ISW),
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85mA (ISW), High Efficiency Step-Up DC/DC Converter
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3463f
8
Linear Technology Corporation
LT/TP 0404 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2003
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