CD43-4R7

LT1945 LINER

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Technical content

Converter with Positive and Negative Outputs 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 20mA at no load, which further reduces to 0.5 mA 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. n Generates Well-Regulated Positive and Negative Outputs n Low Quiescent Current: 20mA in Active Mode (per Converter) <1mA 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 n Small TFT LCD Panels n Handheld Computers n Battery Backup n Digital Cameras , LTC and LT are registered trademarks of Linear Technology Corporation. LOAD CURRENT (mA) 0.1 EFFICIENCY (%) 1 10 100

1945 TA01a

+12V OUTPUT –20V OUTPUT Dual Output (+12V, –20V) Converter Efficiency at VIN = 3.6V VIN SW1 FB2 LT1945 10µH D1 SHDN2 24.9k 365k 1µF –20V 10mA VIN 2.7V TO 5V

1945 TA01

4.7pF 4.7µF 0.1µF NFB12 1SHDN1 10µH D3 115k 1µF 100pF C1: TAIYO YUDEN JMK212BJ475 C2, C3: TAIYO YUDEN TMK316BJ105 C4: TAIYO YUDEN EMK107BJ104 D1, D2, D3: ZETEX ZHCS400 L1, L2: MURATA LQH3C100 12V 20mA

ABSOLUTE AXI U RATI GSW WW U PACKAGE/ORDER I FOR ATIOUU W (Note 1) Operating Temperature Range (Note 2) .. – 40°C to 85°C ORDER PART NUMBER LT1945EMS MS PART MARKING ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage 1.2 V Quiescent Current, (per Converter) Not Switching 20 30 mA VSHDN = 0V 1 mA NFB1 Comparator Trip Point l –1.205 –1.23 –1.255 V FB2 Comparator Trip Point l 1.205 1.23 1.255 V FB Comparator Hysteresis 8m V NFB1, FB2 Voltage Line Regulation 1.2V < V IN < 12V 0.05 0.1 %/V NFB1 Pin Bias Current (Note 3) V NFB1 = –1.23V l 1.3 2 2.9 mA FB2 Pin Bias Current (Note 4) V FB2 = 1.23V l 30 80 nA Switch Off Time, Switcher 1 (Note 5) 400 ns Switch Off Time, Switcher 2 (Note 5) V FB2 > 1V 400 ns VFB2 < 0.6V 1.5 ms Switch VCESAT ISW = 300mA 250 350 mV Switch Current Limit 250 350 400 mA SHDN Pin Current V SHDN = 1.2V 2 3 mA VSHDN = 5V 8 12 mA SHDN Input Voltage High 0.9 V SHDN Input Voltage Low 0.25 V Switch Leakage Current Switch Off, V SW = 5V 0.01 5 mA 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 TJMAX = 125°C, qJA = 160°C/W temperature range, otherwise specifications are at TA = 25°C. VIN = 1.2V, VSHDN = 1.2V unless otherwise noted. LTTS Consult LTC Marketing for parts specified with wider operating temperature ranges. NFB1 SHDN1 GND SHDN2 FB2 SW1 PGND V IN PGND SW2 TOP VIEW MS PACKAGE 10-LEAD PLASTIC MSOP 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.

TYPICAL PERFOR A CE CHARACTERISTICSUW Switch Saturation Voltage (VCESAT) FB2 Pin Voltage and Bias Current TEMPERATURE (°C) –50 –25 0 25 50 75 100 SWITCH VOLTAGE (V)

1945 G01

0.60 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 ISWITCH = 500mA ISWITCH = 300mA TEMPERATURE (°C) –50 FEEDBACK VOLTAGE (V)

1945 G02

1.25 1.24 1.23 1.22 1.21 1.20 BIAS CURRENT (nA) CURRENT VOLTAGE –25 0 25 50 75 100 TEMPERATURE (°C) FEEDBACK VOLTAGE (V)

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–1.25 –1.24 –1.23 –1.22 –1.21 –1.20 –50 –25 0 25 50 75 100 VOLTAGE CURRENT BIAS CURRENT (µA) PI FU CTIO S UU U NFB1 (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. V IN (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. TEMPERATURE (°C) SWITCH OFF TIME (ns)

1945 G04

–50 –25 0 25 50 75 100 VIN = 1.2V VIN = 12V TEMPERATURE (°C) PEAK CURRENT (mA)

1945 G05

–50 –25 0 25 50 75 100 VIN = 12V VIN = 1.2V Switch Off Time Switch Current Limit NFB1 Pin Voltage and Bias Current TEMPERATURE (°C) QUIESCENT CURRENT (µA)

1945 G06

–50 –25 0 25 50 75 100 VIN = 12V VIN = 1.2V VFB = 1.23V NOT SWITCHING

Figure 1. LT1945 Block Diagram in the power switch and in the external inductor and diode.

Table 1. Recommended Inductors Current Limit Overshoot section). without excessive reduction in maximum output current. value to be used for a SEPIC regulator using the LT1945.

minimum VIN value in the equation below. of available output current for smaller inductor values. than 5V), the current limit overshoot can be quite high. be used at the output to minimize the output ripple voltage. very small packages. Y5V ceramics are not recommended. capacitor with a sufficient voltage rating. Table 2. Recommended Capacitors

APPLICATIO S I FOR ATIOWU UU Setting the Output Voltages Set the output voltage for Switcher 1 (negative output voltage ) by choosing the appropriate values for feedback resistors R1 and R2. R VV V R OUT 12 3 12 3 21 0 6 + () - . · Set the output voltage for Switcher 2 (positive output voltage) by choosing the appropriate values for feedback resistors R1B and R2B (see Figure 1). RB R B V V OUT12 12 3 1=- æ Łç ö ł÷. Diode Selection For most LT1945 applications, the Zetex ZHCS400 sur- face mount Schottky diode (0.4A, 40V) is an ideal choice. Schottky diodes, with their low forward voltage drop and fast switching speed, are the best match for the LT1945. The Motorola MBR0520, MBR0530, or MBR0540 can also be used. Many different manufacturers make equivalent parts, but make sure that the component is rated to handle at least 0.35A. Lowering Output Voltage Ripple Using low ESR capacitors will help minimize the output ripple voltage, but proper selection of the inductor and the output capacitor also plays a big role. The LT1945 pro- vides energy to the load in bursts by ramping up the inductor current, then delivering that current to the load. If too large of an inductor value or too small of a capacitor value is used, the output ripple voltage will increase because the capacitor will be slightly overcharged each burst cycle. To reduce the output ripple, increase the output capacitor value or add a 4.7pF feed-forward capaci- tor in the feedback network of the LT1945 (see the circuits in the Typical Applications section). Adding this small, inexpensive 4.7pF capacitor will greatly reduce the output voltage ripple. Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1661) MSOP (MS) 0402 0.53 – 0.01 (.021 – .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) 0.13 – 0.05 (.005 – .002) 0.86 (.034) REF 0.50 (.0197) TYP 12 3 45 4.88 – 0.10 (.192 – .004) 0.497 – 0.076 (.0196 – .003) REF8910 7 6 3.00 – 0.102 (.118 – .004) (NOTE 3) 3.00 – 0.102 (.118 – .004) NOTE 4 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.2 – 3.45 (.126 – .136) 0.889 – 0.127 (.035 – .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 – 0.038 (.0120 – .0015) TYP 0.50 (.0197) BSC

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 l FAX: (408) 434-0507 l www.linear.com ª LINEAR TECHNOLOGY CORPORATION 2001 LT/TP 0802 2K • PRINTED IN USA RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1613 550mA I SW, 1.4MHz, High Efficiency Step-Up DC/DC Converter V IN = 0.9V to 10V, VOUT = 34V, IQ = 3mA, ISD = <1mA, ThinSOT Package LT1615/LT1615-1 300mA I SW, Constant Off-Time, High Efficiency V IN = 1.2V to 15V, VOUT = 34V, IQ = 20mA, ISD = <1mA, Step-Up DC/DC Converter ThinSOT Package LT1940 Dual Output 1.4A (I OUT), Constant 1.1MHz, High Efficiency V IN = 3V to 25V, VOUT = 1.2V, IQ = 2.5mA, ISD = <1mA, Step-Down DC/DC Converter TSSOP-16E Package LT1944 Dual Output 350mA I SW, Constant Off-Time, High Efficiency V IN = 1.2V to 15V, VOUT = 34V, IQ = 20mA, ISD = <1mA, MS Package Step-Up DC/DC Converter LT1944-1 Dual Output 150mA I SW, Constant Off-Time, High Efficiency V IN = 1.2V to 15V, VOUT = 34V, IQ = 20mA, ISD = <1mA, MS Package Step-Up DC/DC Converter LT1949/LT1949-1 550mA I SW, 600kHz/1.1MHz, High Efficiency V IN = 1.5V to 12V, VOUT = 28V, IQ = 4.5mA, ISD = <25mA, Step-Up DC/DC Converter S8, MS8 Packages LTC3400/LTC3400B 600mA I SW, 1.2MHz, Synchronous Step-Up DC/DC Converter V IN = 0.85V to 5V, VOUT = 5V, IQ = 19mA/300mA, ISD = <1mA, ThinSOT Package LTC3401 1A I SW, 3MHz, Synchronous Step-Up DC/DC Converter V IN = 0.5V to 5V, VOUT = 6V, IQ = 38mA, ISD = <1mA, MS Package LTC3402 2A I SW, 3MHz, Synchronous Step-Up DC/DC Converter V IN = 0.5V to 5V, VOUT = 6V, IQ = 38mA, ISD = <1mA, MS Package LTC3423 1A I SW, 3MHz, Low VOUT, Synchronous Step-Up V IN = 0.5V to 5V, VOUT = 6V, IQ = 38mA, ISD = <1mA, MS Package DC/DC Converter LTC3424 2A I SW, 3MHz, Low VOUT, Synchronous Step-Up V IN = 0.5V to 5V, VOUT = 6V, IQ = 38mA, ISD = <1mA, MS Package DC/DC Converter Dual Output (–32V) Converter VIN SW1 FB2 LT1945 10µH D1 SHDN2 24.9k 604k 1µF –32V 5mA VIN 2.7V TO 5V

1945 TA02

4.7pF 4.7µF NFB12 1SHDN1 10µH D3 80.6k 1µF 100pF C1: TAIYO YUDEN JMK212BJ475 C2, C3: TAIYO YUDEN GMK316BJ105 C4: TAIYO YUDEN UMK212BJ104 D1, D2, D3: ZETEX ZHCS400 L1, L2: MURATA LQH3C100 32V 5mA 0.1µF (408)573-4150 (408)573-4150 (408)573-4150 (631)543-7100 (814)237-1431 UTYPICAL APPLICATIO LOAD CURRENT (mA) 0.1 EFFICIENCY (%) 11 0

1945 TA02a

–32V OUTPUT Efficiency at VIN = 3.6V