DN359 - Dual DC/DC Converter with Integrated Schottkys Generates ±40V Outputs and Consumes Only 40µA Quiescent Current

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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
10μH
C1
1μF
3
VIN
9
2
SHDN1
FB1
SHDN2
GND
11
L2
10μH
1
SW1 VOUT1
LT3463
8
R2
1M
VREF
FB2
SW2
D2
4
5
C4
0.1μF
10
R1
66.5k
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respective owners.
VOUT1
20V
9mA
80
20V OUTPUT
C2
0.47μF
7
6
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).
EFFICIENCY (%)
VIN
2.7V
TO 5V
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.
R3
61.9k
–20V OUTPUT
70
60
R4
1M
D1
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
C3
0.47μF
VOUT2
–20V
9mA
50
0.1
1
10
LOAD CURRENT (mA)
100
DN359 F01
DN359 F02
Figure 1. Dual Output ±20V Converter
03/05/359_conv
Figure 2. Efficiency of Circuit in Figure 1 at VIN = 3.6V
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
10μH
VIN
9
2
SHDN1
FB1
VREF
SHDN2
GND
11
R2
1M
1
SW1 VOUT1
LT3463
8
C1
4.7μF
3
VIN
9
FB2
SW2
8
SHDN1
FB1
SHDN2
GND
11
L2
10μH
1
VREF
FB2
SW2
4
10
7
6
R3
154k
D2
5
C4
1μF
R4
1M
D1
R1
32.4k
C5
10pF
VOUT2
–8V
50mA
C3
4.7μF
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
C2
0.22μF
C2
2.2μF
R1
90.9k
DN359 F04
Figure 4. CCD Sensor Bias Supply
7
R3
31.6k
6
80
R4
1M
D2
5
VIN = 3.6V
240
15V EFFICIENCY
200
75
D1
L2
10μH
D1: DIODES, INC. B0540W
L1, L2: MURATA LQH32CN100K53
VOUT2
–40V
C3
0.22μF
DN359 F03
Figure 3. 2.7V to ±40V Dual Output Converter
70
160
–8V EFFICIENCY
120
65
80
60
POWER LOSS (mW)
4 C4
0.1μF
10
2
VOUT1
15V
10mA
R2
1M
SW1 VOUT1
LT3463A
VOUT1
+40V
3
C1
4.7μF
L1
10μH
EFFICIENCY (%)
VIN
2.7V TO 5V
VIN
2.7V
TO 5V
15V LOSS
40
55
–8V LOSS
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 general-purpose TFT display bias supply for
portable devices. Figure 5 shows the efficiency and
power loss data for the circuit.
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Linear Technology Corporation
50
0.1
1
10
LOAD CURRENT (mA)
0
100
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.
For applications help,
call (408) 432-1900
dn359f_conv LT/TP 0305 305K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005
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