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Linear Technology Electronic Components Datasheet


LQH3C4R7

Dual Micropower DC/DC Converter with Positive and Negative Outputs


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LQH3C4R7 pdf
FEATURES
s Generates Well-Regulated Positive and
Negative Outputs
s Low Quiescent Current:
20µA in Active Mode (per Converter)
<1µA in Shutdown Mode
s Operates with VIN as Low as 1.2V
s Low VCESAT Switch: 250mV at 300mA
s Uses Small Surface Mount Components
s High Output Voltage: Up to ±34V
s Tiny 10-Pin MSOP Package
U
APPLICATIO S
s Small TFT LCD Panels
s Handheld Computers
s Battery Backup
s Digital Cameras
LT1945
Dual Micropower DC/DC
Converter with Positive and
Negative Outputs
DESCRIPTIO
The LT®1945 is a dual micropower DC/DC converter in a
10-pin MSOP package. Each converter is designed with a
350mA current limit and an input voltage range of 1.2V to
15V, making the LT1945 ideal for a wide variety of appli-
cations. Both converters feature a quiescent current of
only 20µA at no load, which further reduces to 0.5µA 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 36V switch allows
high voltage outputs up to ±34V to be easily generated
without the use of costly transformers. The LT1945’s low
off-time of 400ns permits the use of tiny, low profile
inductors and capacitors to minimize footprint and cost in
space-conscious portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
2.7V
TO 5V
C1
4.7µF
Dual Output (+12V, –20V) Converter
L1
10µH
C4
0.1µF
D1
8 10
VIN
2
SHDN1
SW1
1
NFB1
LT1945
4
SHDN2
5
FB2
GND PGND PGND SW2
37 96
D2
100pF 365k
24.9k
–20V
10mA
C2
1µF
115k
L2
10µH
C1: TAIYO YUDEN JMK212BJ475
C2, C3: TAIYO YUDEN TMK316BJ105
C4: TAIYO YUDEN EMK107BJ104
D1, D2, D3: ZETEX ZHCS400
L1, L2: MURATA LQH3C100
4.7pF
D3
C3
1M 1µF
12V
20mA
1945 TA01
Efficiency at VIN = 3.6V
90
85
+12V OUTPUT
80
–20V OUTPUT
75
70
65
60
55
50
0.1
1 10
LOAD CURRENT (mA)
100
1945 TA01a
1945f
1



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LQH3C4R7 pdf
LT1945
ABSOLUTE AXI U RATI GS
(Note 1)
VIN, SHDN1, SHDN2 Voltage ................................... 15V
SW1, SW2 Voltage .................................................. 36V
NFB1 Voltage ........................................................... –3V
FB2 Voltage ...............................................................VIN
Current into NFB1 Pin ........................................... –1mA
Current into FB2 Pin .............................................. 1mA
Junction Temperature ........................................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
UW U
PACKAGE/ORDER I FOR ATIO
NFB1 1
SHDN1 2
GND 3
SHDN2 4
FB2 5
TOP VIEW
10 SW1
9 PGND
8 VIN
7 PGND
6 SW2
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 160°C/W
ORDER PART
NUMBER
LT1945EMS
MS PART MARKING
LTTS
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The q denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted.
PARAMETER
CONDITIONS
Minimum Input Voltage
Quiescent Current, (per Converter)
NFB1 Comparator Trip Point
Not Switching
VSHDN = 0V
FB2 Comparator Trip Point
FB Comparator Hysteresis
NFB1, FB2 Voltage Line Regulation
NFB1 Pin Bias Current (Note 3)
FB2 Pin Bias Current (Note 4)
Switch Off Time, Switcher 1 (Note 5)
1.2V < VIN < 12V
VNFB1 = –1.23V
VFB2 = 1.23V
Switch Off Time, Switcher 2 (Note 5)
Switch VCESAT
Switch Current Limit
VFB2 > 1V
VFB2 < 0.6V
ISW = 300mA
SHDN Pin Current
SHDN Input Voltage High
VSHDN = 1.2V
VSHDN = 5V
SHDN Input Voltage Low
Switch Leakage Current
Switch Off, VSW = 5V
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1945 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the – 40°C to 85°C operating
MIN
q –1.205
q 1.205
q 1.3
q
250
0.9
TYP
20
–1.23
1.23
8
0.05
2
30
400
400
1.5
250
350
2
8
0.01
MAX
1.2
30
1
–1.255
1.255
0.1
2.9
80
350
400
3
12
0.25
5
UNITS
V
µA
µA
V
V
mV
%/V
µA
nA
ns
ns
µs
mV
mA
µA
µA
V
V
µA
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Bias current flows out of the NFB1 pin.
Note 4: Bias current flows into the FB2 pin.
Note 5: See Figure 1 for Switcher 1 and Switcher 2 locations.
1945f
2



Part Number LQH3C4R7
Description Dual Micropower DC/DC Converter with Positive and Negative Outputs
Maker Linear Technology - Linear Technology
Total Page 8 Pages
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