advertisement
Dual DC/DC Converter with Integrated Schottkys Generates
±40V Outputs and Consumes Only 40µA Quiescent Current
Design Note 359
David Kim
Introduction
As portable devices become more sophisticated and
require higher display resolution, there is an increased
demand for accurate, high voltage bias supply solutions
with wide input and output voltage ranges. The traditional
methods of using arrays of capacitors to implement a
charge pump or a bulky and expensive transformer no
longer meet the accuracy and size requirements of today’s
portable devices.
®
The LT
3463 is both accurate and compact. It fits both a
positive output converter plus a negative output converter
into a tiny (3mm × 3mm)DFN package, including Schottky
diodes and switches capable of 250mA (400mA on the
negative channel of the LT3463A).
The LT3463 works in a wide range of applications due to
its 2.3V to 15V input voltage range and output capability
to ±40V. Each converter is designed to operate with a
quiescent current of only 20µA, which drops to less than
1µA in shutdown, making the LT3463 solution ideal for
battery-powered portable applications.
L1
V
2.7V
TO 5V
IN
C1
1µF
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
10µH
321
LT3463
SW1
0.1µF
V
OUT1
FB1
V
FB2
D2
C4
V
IN
9
SHDN1
8
SHDN2
GND4SW2
11
L2
10µH
REF
R2
1M
10
7
6
5
R1
66.5k
R3
61.9k
R4
1M
D1
C3
0.47µF
Figure 1. Dual Output ±20V Converter Figure 2. Efficiency of Circuit in Figure 1 at VIN = 3.6V
C2
0.47µF
DN359 F01
V
OUT1
20V
9mA
V
OUT2
–20V
9mA
Dual Output ±20V Converter
Figure 1 shows a ±20V LCD bias voltage supply using the
LT3463. This circuit generates both positive and negative 20V outputs from a Li-Ion battery. Low profile
inductors and capacitors keep the circuit under 9mm ×
9.5mm × 1.2mm, making this circuit ideal for small
wireless devices such as cellular phones or DSCs.
This design can produce ±20V at 9mA from a 2.7V input
and up to 20mA from a 5V input. The efficiency shown in
Figure 2 exceeds 70% over a wide load current range reaching 75% at 20mA. The LT3463’s constant off-time architecture allows 20µA quiescent current operation for each
output, making the LCD bias circuit efficient even at 100µA
load current. This circuit can accommodate different load
voltages as the LCD bias voltage varies for different manufacturers (typically 9V ~ 25V).
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
80
20V OUTPUT
70
EFFICIENCY (%)
60
50
0.1
–20V OUTPUT
110100
LOAD CURRENT (mA)
DN359 F02
03/05/359
Dual Output (±40V) Converter
The circuit in Figure 3 demonstrates the impressive input
and output voltage range of the LT3463. As shown, the
42V internal switches allow up to ±40V output without a
transformer or an array of diodes and capacitors. The
output voltages can be easily changed by adjusting the
values of R1 and R3. The circuit is designed to operate
from a Li-Ion battery or two alkaline cells (down to 2.4V).
L1
9
8
10µH
3
V
IN
SHDN1
SHDN2
GND
11
L2
10µH
21
V
SW1
OUT1
FB1
LT3463
V
REF
FB2
D2
SW2
4
C4
0.1µF
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
V
OUT1
R2
1M
10
R1
32.4k
7
R3
31.6k
6
R4
5
1M
D1
+40V
C2
0.22µF
V
–40V
C3
0.22µF
DN359 F03
OUT2
V
2.7V TO 5V
4.7µF
IN
C1
Figure 3. 2.7V to ±40V Dual Output Converter
CCD Sensor Bias Supply
The circuit in Figure 4 shows a CCD sensor bias supply for
a cellular camera phone application. The two outputs, 15V
and –8V, are generated from a Li-Ion battery input. With
a minimum input voltage of 3.3V, the circuit is designed
to output 15V at 10mA and –8V at 40mA to accommodate
the maximum current consumption of the CCD sensor.
The low power consumption of the LT3463 and its small
circuit size also make this solution ideal as a generalpurpose TFT display bias supply for portable devices.
Figure 5 shows the efficiency and power loss data for the
circuit.
V
2.7V
TO 5V
IN
4.7µF
C1
V
IN
9
8
SHDN2
GND SW2 D2
11 4 5
L2
10µH
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
10µH
LT3463A
SW1
1µF
R2
123
V
OUT1
10
FB1SHDN1
7
V
REF
6
FB2
C4
1M
R1
90.9k
R3
154k
R41MC5
D1
C3
4.7µF
10pF
DN359 F04
C2
2.2µF
V
OUT1
15V
10mA
V
OUT2
–8V
50mA
L1
Figure 4. CCD Sensor Bias Supply
80
15V EFFICIENCY
75
70
65
EFFICIENCY (%)
60
55
50
0.1
VIN = 3.6V
–8V EFFICIENCY
15V LOSS
–8V LOSS
1 10 100
LOAD CURRENT (mA)
240
200
POWER LOSS (mW)
160
120
80
40
0
DN359 F05
Figure 5. Efficiency and Power Loss
for the Circuit in Figure 4
Conclusion
The LT3463/LT3463A are ideal solutions for high resolution portable display applications requiring multiple (positive and negative) high output voltages, wide input voltage
range, low quiescent current, small circuit size and accurate output regulation.
Data Sheet Download
http://www.linear.com
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
For applications help,
call (408) 432-1900, Ext. 2759
dn359f LT/TP 0305 305K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 2005
Loading...