DN223 - SOT-23 DC/DC Converters Generate Up to ±35V Outputs and Consume Only 20µA of Quiescent Current

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SOT-23 DC/DC Converters Generate Up to ±35V Outputs and
Consume Only 20µA of Quiescent Current – Design Note 223
Bryan Legates
Today’s portable devices need small power supply solutions that operate with a minimum of supply current.
To meet these needs, Linear Technology introduces the
LT®1615, LT1615-1, LT1617 and LT1617-1 micropower
SOT-23 DC/DC converters. With an input voltage range
as low as 1V and an output voltage range as high as
±35V, these devices provide considerable power supply
design flexibility.
The LT1615 and LT1615-1 are designed to regulate
positive output voltages, whereas the LT1617 and
LT1617-1 are designed to directly regulate negative output voltages without the need for feedback
level-shifting circuitry. The LT1615 and LT1617 have a
350mA current limit and a minimum input voltage of
1.2V, whereas the LT1615-1 and LT1617-1 have a lower,
100mA current limit and a minimum input voltage of
1V. All four converters use tiny, low profile inductors
and capacitors to minimize the overall system footprint
and cost. With a quiescent current of only 20μA and
a shutdown current of 0.5μA, these devices squeeze
the most life out of any battery-powered application.
±20V Dual-Output Converter
with Output Disconnect
Today, most portable devices use a liquid crystal display
(LCD). Different manufacturers require substantially different bias voltages for their LCDs. Typically, a single 9V
to 25V supply is needed (either positive or negative), but
some LCDs require both a positive and negative supply.
Figure 1 shows a ±20V dual-output converter ideally
suited for LCD bias applications needing both supplies.
Both outputs are developed using charge pumps, so
both are disconnected from the input when the LT1617
is turned off. Because the supplies are generated in
the same manner, this circuit features excellent cross
regulation: for a 5× difference in output currents, the
positive and negative output voltages differ less than
1%; for a 10× difference, they differ less than 2%. A
similar circuit can be implemented using the LT1615 if
the regulation of the positive output is more important.
As shown in Figure 2, efficiency reaches 78% with a
fresh 4-cell alkaline battery.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
D3
C5
0.1μF
D2
C4
0.1μF
L1
10μH
5
1
VIN
SW
85
D1
–20V
4mA
4
SHDN
C2
1μF
100pF
D4
267k
LT1617
C1
4.7μF
NFB
3
GND
80
VIN = 6V
75
VIN = 3.3V
70
65
60
24.9k
2
C1: TAIYO YUDEN LMK316BJ475
C2, C3: TAIYO YUDEN TMK316BJ105
C4, C5: TAIYO YUDEN UMK212BJ104
L1: MURATA LQH3C100K24
D1, D2, D3, D4: MOTOROLA MBR0530
55
(408) 573-4150
(408) 573-4150
(408) 573-4150
(814) 237-1431
(800) 441-2447
Figure 1. ± 20V Dual Output Converter
with Output Disconnect
02/00/223_conv
90
EFFICIENCY (%)
VIN
1.5V TO 6V
20V
4mA
C3
1μF
DN223 F01
50
0.1
1
10
LOAD CURRENT FOR EACH OUTPUT (mA)
DN223 F02
Figure 2. ± 20V Dual Output Converter Efficiency
24V Boost Converter
Figure 3 shows a circuit ideal for LCD applications needing only a positive bias voltage. This 24V boost converter
delivers 10mA from a nearly discharged single Li-Ion
cell. An input voltage as low as 1.5V can be used with
this converter, but the output current capability reduces
to 5mA. Converter efficiency is shown in Figure 4.
L1
10μH
VIN
2.5V TO 6V
5
D1
24V
10mA
1
VIN
SW
C1
4.7μF
SHDN
FB
L1
22μH
VIN
1V TO 6V
1.07M
C2
1μF
LT1615
4
1-Cell to 3V Boost Converter
A 1-cell alkaline to 3V boost converter using the
LT1615-1 is shown in Figure 6. Capable of providing
15mA of output current, this converter occupies a board
area less than 1/4" by 5/16" (less than 0.078 inches2).
See Figure 7 for converter efficiency, which reaches
75% with a fresh 1-cell alkaline battery.
3
GND
4
1
VIN
SW
Figure 3. 24V Boost Converter
GND
EFFICIENCY (%)
75
(408) 573-4150
(408) 573-4150
(800) 441-2447
(814) 237-1431
L1
4.7μH
VIN = 2.5V
D1
5
1
VIN
SW
4
65
C1
4.7μF
60
100
DN223 F04
100k
NFB
357k
3
GND
249k
2
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN JMK316BJ106
D1: CENTRAL SEMI CMDSH-3
L1: MURATA LQH3C4R7M24
55
1
10
LOAD CURRENT (mA)
SHDN
3V
15mA
C2
10μF
4.7pF
LT1615-1
70
50
0.1
DN223 F05
Figure 5. 1V to 35V Boost Converter
VIN
1V TO 1.5V
80
365k
2
90
VIN = 6V
C2
1μF
3
FB
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN GMK316BJ105
D1: MOTOROLA MBR0540
L1: MURATA LQH3C220K34
DN223 F03
85
35V
500μA
10M
SHDN
C1
4.7μF
57.6k
(408) 573-4150
(408) 573-4150
(800) 441-2447
(814) 237-1431
5
LT1615-1
2
C1: TAIYO YUDEN LMK316BJ475
C2: TAIYO YUDEN TMK316BJ105
D1: MOTOROLA MBR0530
L1: MURATA LQH3C100K24
D1
(408) 573-4150
(408) 573-4150
(800) 441-2447
(814) 237-1431
DN223 F06
Figure 6. 1-Cell Alkaline to 3V Boost Converter
Figure 4. 24V Boost Converter Efficiency
80
Data Sheet Download
www.linear.com
Linear Technology Corporation
VIN = 1.5V
75
VIN = 1V
EFFICIENCY (%)
1V to 35V Boost Converter
The circuit in Figure 5 shows the impressive input and
output voltage range of the LT1615-1. As shown, the
circuit will work from one to four alkaline cells or a
single cell Li-Ion battery. The maximum input voltage
for this circuit is limited by the 6.3V voltage rating on
the input capacitor, C1. The LT1615-1 can operate with
an input voltage as high as 15V. The output current is
limited by the 1V minimum input (this converter can
provide 2mA with a 3V input). If a larger output current
is needed, but operation from a 1V input is not required,
use an LT1615 in place of the LT1615-1 to obtain a 3×
increase in maximum output current.
70
65
60
55
50
0.1
1
10
LOAD CURRENT (mA)
DN223 F07
Figure 7. 1-Cell to 3V Boost Converter Efficiency
For applications help,
call (408) 432-1900
dn223f_conv LT/TP 0200 340K • PRINTED IN THE USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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© LINEAR TECHNOLOGY CORPORATION 2000
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