LT1611 LINER | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 12
Technical content
“charge pump” solutions in many applications. The LT1611 is available in the 5-lead SOT-23 package.
1611 TA01
Figure 1. 5V to – 5V, 150mA Low Noise Inverting DC/DC Converter , LTC and LT are registered trademarks of Linear Technology Corporation.
ABSOLUTE MAXIMUM RATINGSW WW U PACKAGE/ORDER INFORMATIONW UU ORDER PART NUMBER LT1611CS5 TJMAX = 125°C, qJA = 256°C/W S5 PART MARKING LTES Consult factory for Industrial and Military grade parts. SW 1 GND 2 TOP VIEW S5 PACKAGE 5-LEAD PLASTIC SOT-23 NFB 3
5 VIN
4 SHDN
(Note 1) Operating Temperature Range
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage 0.9 1.1 V Maximum Operating Voltage 10 V NFB Pin Bias Current V NFB = –1.23V l – 2.7 – 4.7 – 6.7 mA Feedback Voltage l –1.205 – 1.23 –1.255 V Quiescent Current V SHDN = 1.5V, Not Switching 3 4.5 mA Quiescent Current in Shutdown V SHDN = 0V, VIN = 2V 0.01 0.5 mA VSHDN = 0V, VIN = 5V 0.01 1.0 mA Reference Line Regulation 1.5V £ VIN £ 10V 0.02 0.2 %/V Switching Frequency l 1.0 1.4 1.8 MHz Maximum Duty Cycle l 82 86 % Switch Current Limit (Note 3) 550 800 mA Switch VCESAT ISW = 300mA 300 350 mV Switch Leakage Current V SW = 5V 0.01 1 mA SHDN Input Voltage High 1V SHDN Input Voltage Low 0.3 V SHDN Pin Bias Current V SHDN = 3V 25 50 mA VSHDN = 0V 0 0.1 mA Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: C grade device specifications are guaranteed over the 0°C to 70°C temperature range. In addition, C grade device specifications are assured over the –40 °C to 85°C temperature range by design or correlation, but are not production tested. Note 3: Current limit guaranteed by design and/or correlation to static test. Slope compensation reduces current limit at higher duty cycle. The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 1.5V, VSHDN = VIN unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICSUW LOAD CURRENT (mA) EFFICIENCY (%)
1611 G01
VIN = 3V VIN = 5V TEMPERATURE (°C) –50 0 50–25 25 75 100 NFB PIN BIAS CURRENT (µA)
1611 G03
SWITCH CURRENT (mA) 0 100 200 300 400 500 600 700 VCESAT (mV)
1611 G04
TA = 25°C SHDN PIN VOLTAGE (V) 012345 SHDN PIN BIAS CURRENT (µA)
1611 G05
DUTY CYCLE (%) SWITCH CURRENT LIMIT (mA) 900 800 700 600 500 400 300 200 100
1611 G06
TA = 25°C TEMPERATURE (°C) –50 –25 0 25 50 75 100 SWITCHING FREQUENCY (MHz)
1611 G07
2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 VIN = 5V VIN = 1.5V TEMPERATURE (°C) –50 SWITCH CURRENT LIMIT (mA) 900 800 700 600 500 400 300 200 100
1611 G09
–25 0 25 50 75 100 Efficiency, VOUT = – 5V NFB Pin Bias Current vs TemperatureVNFB vs Temperature Switch VCESAT vs Switch Current Switch Current Limit vs Duty CycleSHDN Pin Bias Current vs VSHDN Oscillator Frequency vs Temperature Switch Current Limit vs Temperature (Duty Cycle = 30%) No-Load Operating Quiescent Current vs Temperature* TEMPERATURE (°C) –50 0 50–25 25 75 100 VNFB (V)
1611 G02
–1.245 –1.240 –1.235 –1.230 –1.225 –1.220 –1.215 –1.210 TEMPERATURE (°C) –50 0 50–25 25 75 100 OPERATING CURRENT (mA)
1611 G08
6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 * Includes bias current through R1, R2 and Schottky leakage current at T ‡ 75°C
SW (Pin 1): Switch Pin. Minimize trace area at this pin to keep EMI down. GND (Pin 2): Ground. Tie directly to local ground plane. NFB (Pin 3): Negative Feedback Pin. Minimize trace area. Reference voltage is –1.23V. Connect resistive divider tap here. The suggested value for R2 is 10k. Set R1 and R2 according to: R V R OUT1 12 3 12 3 2 45 10 6 + æ Ł ö ł . .• SHDN (Pin 4): Shutdown Pin. Tie to 1V or more to enable device. Ground to shut the device down. VIN (Pin 5): Input Supply Pin. Must be locally bypassed. BLOCK DIAGRAMW + – FF RQ S 0.15Ω SW DRIVER COMPARATOR 2SHUTDOWN SHDN SRAMP GENERATOR RC CC 1.4MHz OSCILLATOR GND 1611 BD 40k 140k 30k x10 40k VINVIN 5 NFB CPL (OPTIONAL) (EXTERNAL) (EXTERNAL) VOUT NFB A = 3 gm OPERATIOU The LT1611 combines a current mode, fixed frequency PWM architecture with a –1.23V reference to directly regulate negative outputs. Operation can be best under- stood by referring to the block diagram of Figure 2. Q1 and Q2 form a bandgap reference core whose loop is closed around the output of the converter. The driven reference point is the lower end of resistor R4, which normally sits at a voltage of –1.23V. As the load current changes, the NFB pin voltage also changes slightly, driving the output of g m amplifier A1. Switch current is regulated directly on a cycle-to-cycle basis by A1’s output. The flip-flop is set at the beginning of each cycle, turning on the switch. When the summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscil- lations at duty factors greater than 50%) exceeds the V C signal, comparator A2 changes stage, resetting the flip- Figure 2 flop and turning off the switch. Output voltage decreases (the magnitude increases) as switch current is increased. The output, attenuated by external resistor divider R1 and R2, appears at the NFB pin, closing the overall loop. Frequency compensation is provided internally by R C and CC. Transient response can be optimized by the addition of a phase lead capacitor, CPL, in parallel with R1 in applica- tions where large value or low ESR output capacitors are used. As load current is decreased, the switch turns on for a shorter period each cycle. If the load current is further decreased, the converter will skip cycles to maintain output voltage regulation. The LT1611 can work in either of two topologies. The simpler topology appends a capacitive level shift to a
LT1611’s internal switch is off. the SW node voltage abruptly increases to (VIN + |VOUT|). The SWX node voltage increases to V D (about 350mV). continues to be supplied by L2 and C3. switching noise will be introduced into the ground plane. present on switching regulator outputs. low ESR, high value capacitors.
1611 F03
1611 F04
Figure 3. Direct Regulation of Negative Output Figure 4. L2 Replaces D2 to Make Low Output Ripple
1611 F05
1611 F06
Figure 5. Switch-On Phase of Inverting Converter. L1 and L2 Current Have Positive dI/dt Figure 6. Switch-Off Phase of Inverting Converter. L1 and L2 Current Have Negative dI/dt
mately 100mV as the load changes from 50mA to 150mA. adding a 3.3nF capacitor (C PL) as shown in Figure 9. layout, described in the next section.
1611 F07
Figure 7. Switching RL2 Provides 50mA to 150mA Figure 8. Load Step Response of LT1611 Figure 9. Addition of C Figure 10. 22mF “B” Case Tantalum Capacitor (AVX TAJ “B” Series)
layout is mandatory to achieve this level of performance. Figure 11. Replacing C3 with 22mF Ceramic Capacitor Figure 12. 22mF Ceramic Capacitor at Figure 13. Suggested Component Placement. Note Cut in Ground Copper at D1’s Cathode
1611 F13
1611 F14
Figure 14. RSS and CSS at SHDN Pin Provide Soft-Start to LT1611 Inverting Converter Figure 15. RSS = 33k, CSS = 33nF; VOUT Reaches Figure 16. RSS = 33k, CSS = 0.1mF; VOUT Reaches
delivered when driving L1A from a 12V supply. whose components are suitable.
1611 F17
1611 F18
Figure 17. Increase Output Current By Driving L1A from a Higher Voltage Figure 18. Output Current Increases to
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. Table 1. Inductor Vendors Table 2. Capacitor Vendors lower cost applications, small tantalum units can be used. LT1611 are listed in Table 2. A Schottky diode is recommended for use with the LT1611.
1611 TA02
1611f LT/TP 0999 4K • PRINTED IN USA ª LINEAR TECHNOLOGY CORPORA TION 1 998 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1307 Single Cell Micropower DC/DC with Low Battery Detector 3.3V/75mA from 1V, 600kHz Fixed Frequency LT1316 Burst Mode TM Operation DC/DC with Programmable Current Limit 1.5V Minimum V IN, Precise Control of Peak Switch Current LT1317 2-Cell Micropower DC/DC with Low Battery Detector 3.3V/200mA from Two Cells, 600kHz Fixed Frequency LT1370/LT1371 500kHz High Efficiency DC/DC Converter 42V, 6A/3A Internal Switch, Negative Feedback Regulation LT1610 Single Cell Micropower DC/DC 3V/30mA from 1V, 1.7MHz Fixed Frequency, 30 mA IQ LT1613 1.4MHz SOT-23 Step-Up DC/DC Converter 5V at 200mA from 3.3V Input LT1614 Inverting Mode Switching Regulator with Low-Battery Detector –5V at 200mA from 5V Input in MSOP LT1615 Micropower SOT-23 Step-Up DC/DC Converter 20 mA Quiescent Current, VOUT Up to 34V LT1617 Micropower SOT-23 Inverting Regulator V OUT Up to –34V, 20mA Quiescent Current Burst Mode is a trademark of Linear Technology Corporation. Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 l FAX: (408) 434-0507 l www.linear-tech.com LOAD CURRENT (mA) 0 25 50 75 100 125 150 EFFICIENCY (%)
1611 TA04
VIN = 6.5V VIN = 5V VIN = 3.6V 4-Cell to –10V Inverting Converter Efficiency PACKAGE DESCRIPTIONU Dimensions in inches (millimeters) unless otherwise noted. 5-Lead Plastic SOT-23 (LTC DWG # 05-08-1633) TYPICAL APPLICATIO SU VIN VIN VOUT –10V/60mA
1611 TA03
15µH L1B 15µH GND LT1611 22µF 6.8µF 1µF 10k 68.1k NFBSHDNSHUTDOWN C1: AVX TAJB226M010 (803) 946-0362 C2: TAIYO YUDEN LMK212BJ105MG C3: AVX TAJA685M016 D1: MOTOROLA MBR0520 (800) 441-2447 L1: SUMIDA CL562-150 (847) 956-0666 4-Cell to –10V Inverting Converter 1.50 – 1.75 (0.059 – 0.069) 0.35 – 0.55 (0.014 – 0.020) FIVE PLACES (NOTE 2) S5 SOT-23 0599 0.90 – 1.45 (0.035 – 0.057) 0.90 – 1.30 (0.035 – 0.051) 0.00 – 0.15 (0.00 – 0.006) 0.09 – 0.20 (0.004 – 0.008) (NOTE 2) 2.60 – 3.00 (0.102 – 0.118) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DIMENSIONS ARE INCLUSIVE OF PLATING 3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 4. MOLD FLASH SHALL NOT EXCEED 0.254mm 5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ) 0.95 (0.037) REF 2.80 – 3.00 (0.110 – 0.118) (NOTE 3) 1.90 (0.074) REF