LINEAR TECHNOLOGY LT1944 Technical data
FEATURES
LT1944
Dual Micropower Step-Up
DC/DC Converter
U
DESCRIPTIO
■
Low Quiescent Current:
20µA in Active Mode
<1µA in Shutdown Mode
■
Operates with VIN as Low as 1.2V
■
Low V
■
Uses Small Surface Mount Components
■
High Output Voltage: Up to 34V
■
Tiny 10-Pin MSOP Package
Switch: 250mV at 300mA
CESAT
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APPLICATIO S
■
LCD Bias
■
Handheld Computers
■
Battery Backup
■
Digital Cameras
U
TYPICAL APPLICATIO
The LT®1944 is a dual micropower step-up 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 LT1944 ideal for a wide
variety of applications. 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 in a simple boost topology without the use of
costly transformers. The LT1944’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.
Dual Output (5V, 30V) Boost Converter 5V Output Efficiency
V
IN
2.7V
TO 4.2V
C1
4.7µF
C1: TAIYO YUDEN JMK212BJ475
C2: TAIYO YUDEN JMK316BJ106
C3: TAIYO YUDEN GMK316BJ105
D1, D2: ON SEMI MBR0540
L1: MURATA LQH3C4R7
L2: MURATA LQH3C100
810
V
IN
2
SHDN1
4
SHDN2
PGND9PGND
GND
3
L2
10µH
L1
4.7µH
LT1944
7
SW1
FB1
FB2
SW2
D1
4.7pF
1
5
6
4.7pF
D2
1M
324k
86.6k
2M
5V
80mA
C2
10µF
C3
1µF
30V
8mA
1944 TA01
90
85
VIN = 4.2V
80
75
70
65
EFFICIENCY (%)
60
55
50
0.1
VIN = 2.7V
1 10 100
LOAD CURRENT (mA)
1944 TA01a
1
LT1944
1
2
3
4
5
FB1
SHDN1
GND
SHDN2
FB2
10
9
8
7
6
SW1
PGND
V
IN
PGND
SW2
TOP VIEW
MS10 PACKAGE
10-LEAD PLASTIC MSOP
WW
W
ABSOLUTE AXI U RATI GS
U
UUW
PACKAGE/ORDER I FOR ATIO
(Note 1)
ORDER PART
VIN, SHDN1, SHDN2 Voltage ................................... 15V
SW1, SW2 Voltage .................................................. 36V
FB1, FB2 Voltage .......................................................V
IN
NUMBER
LT1944EMS
Current into FB1, FB2 Pins ..................................... 1mA
Junction Temperature........................................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
T
= 125°C, θJA = 160°C/W
JMAX
MS10 PART
MARKING
LTTR
Lead Temperature (Soldering, 10 sec).................. 300°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, V
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage 1.2 V
Quiescent Current, Each Switcher Not Switching 20 30 µA
= 0V 1 µA
V
SHDN
FB Comparator Trip Point ● 1.205 1.23 1.255 V
FB Comparator Hysteresis 8mV
FB Voltage Line Regulation 1.2V < VIN < 12V 0.05 0.1 %/V
FB Pin Bias Current (Note 3) VFB = 1.23V ● 30 80 nA
Switch Off Time VFB > 1V 400 ns
< 0.6V 1.5 µs
V
FB
Switch V
CESAT
Switch Current Limit 250 350 400 mA
SHDN Pin Current V
SHDN Input Voltage High 0.9 V
SHDN Input Voltage Low 0.25 V
Switch Leakage Current Switch Off, VSW = 5V 0.01 5 µA
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1944 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: Bias current flows into the FB pin.
I
= 300mA 250 350 mV
SW
= 1.2V 2 3 µA
SHDN
= 5V 8 12 µA
V
SHDN
The ● denotes the specifications which apply over the full operating
= 1.2V unless otherwise noted.
SHDN
2
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
(V
) Quiescent Current
CESAT
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
SWITCH VOLTAGE (V)
0.20
0.15
0.10
–25 0 25 50 75 100
–50
I
= 500mA
SWITCH
I
= 300mA
SWITCH
TEMPERATURE (°C)
1944 G01
Switch Off Time Shutdown Pin CurrentSwitch Current Limit
550
500
450
400
350
SWITCH OFF TIME (ns)
300
250
–50 –25 0 25 50 75 100
VIN = 1.2V
VIN = 12V
TEMPERATURE (°C)
1944 G04
Feedback Pin Voltage and
Bias Current
1.25
1.24
VOLTAGE
1.23
1.22
FEEDBACK VOLTAGE (V)
1.21
1.20
–50
–25 0 25 50 75 100
400
VIN = 12V
350
300
250
200
150
PEAK CURRENT (mA)
100
50
0
–50 –25 0 25 50 75 100
CURRENT
TEMPERATURE (°C)
VIN = 1.2V
TEMPERATURE (°C)
1944 G02
1944 G05
50
40
BIAS CURRENT (nA)
30
20
10
0
QUIESCENT CURRENT (µA)
SHUTDOWN PIN CURRENT (µA)
LT1944
25
VFB = 1.23V
NOT SWITCHING
23
21
19
17
15
–50 –25 0 25 50 75 100
25
20
15
10
5
0
0 5 10 15
VIN = 12V
VIN = 1.2V
TEMPERATURE (°C)
1944 G03
25°C
100°C
SHUTDOWN PIN VOLTAGE (V)
1944 G03
UUU
PI FU CTIO S
FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
SHDN1 (Pin 2): Shutdown Pin for Switcher 1. Tie this pin
to 0.9V or higher to enable device. Tie below 0.25V to turn
it off.
GND (Pin 3): Ground. Tie this pin directly to the local
ground plane.
SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin
to 0.9V or higher to enable device. Tie below 0.25V to turn
it off.
FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output
voltage by selecting values for R1B and R2B.
SW2 (Pin 6): Switch Pin for Switcher 2. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
PGND (Pins 7, 9): Power Ground. Tie these pins directly
to the local ground plane. Both pins must be tied.
VIN (Pin 8): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
SW1 (Pin 10): Switch Pin for Switcher 1. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
3
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