Document
FEATURES
n Generates Well-Regulated Positive and Negative Outputs
n Low Quiescent Current: 20μA in Active Mode (per Converter) <1μA in Shutdown Mode
n Operates with VIN as Low as 1.2V n Low VCESAT Switch: 250mV at 300mA n Uses Small Surface Mount Components n High Output Voltage: Up to ±34V n Tiny 10-Pin MSOP Package
APPLICATIONS
n Small TFT LCD Panels n Handheld Computers n Battery Backup n Digital Cameras
LT1945
Dual Micropower DC/DC Converter with Positive and
Negative Outputs
DESCRIPTION
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 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 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.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Dual Output (+12V, –20V) Converter
VIN 2.7V TO 5V
C1 4.7μF
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
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
115k 1M
C3 1μF
12V 20mA
1945 TA01
EFFICIENCY (%)
90 85 80 75 70 65 60 55 50
0.1
Efficiency at VIN = 3.6V
+12V OUTPUT –20V OUTPUT
1 10 LOAD CURRENT (mA)
100
1945 TA01a
1945fa
1
LT1945
ABSOLUTE MAXIMUM RATINGS
(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
PIN CONFIGURATION
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 INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1945EMS#PBF
LT1945EMS#TRPBF
LTTS
10-Lead Plastic MSOP
–40°C to 85°C
LT1945IMS#PBF
LT1945IMS#TRPBF
LTTS
10-Lead Plastic MSOP
–40°C to 125°C
LEAD BASED FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT1945EMS
LT1945EMS#TR
LTTS
10-Lead Plastic MSOP
–40°C to 85°C
LT1945IMS
LT1945IMS#TR
LTTS
10-Lead Plastic MSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS The l 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
MIN TYP MAX UNITS
Minimum Input Voltage
1.2 V
Quiescent Current, (per Converter) NFB1 Comparator Trip Point FB2 Comparator Trip Point FB Comparator Hysteresis
Not Switching VSHDN = 0V
–40°C < TJ < 85°C –40°C < TJ < 125°C
–40°C < TJ < 85°C –40°C < TJ < 125°C
–1.205 –1.195
1.205 1.195
20 –1.23 1.23
8
30 1
–1.255 1.255
1.255 1.255
μA μA
V V
V V
mV
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
–40°C < TJ < 85°C –40°C < TJ < 125°C
0.05 0.1
l 1.3 2 2.9
30 80 300
400
%/V
μA
nA nA ns
Switch Off Time, Switcher 2 (Note 5)
Switch VCESAT Switch Current Limit
VFB2 > 1V VFB2 < 0.6V
ISW = 300mA
400 1.5
250 350
250 350 400
ns μs
mV
mA
1945fa
2
LT1945
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V u.