Final Electrical Specifications LT1614 Inverting 600kHz Switching Regulator July 1998 U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ The LT ®1614 is a fixed frequency, inverting mode switching reglator that operates from an input voltage as low as 1V. Utilizing a low noise topology, the LT1614 can generate a negative output down to – 24V from a 1V to 5V input. Fixed frequency switching ensures a clean output free from low frequency noise. The device contains a lowbattery detector with a 200mV reference and shuts down to less than 10µA. No load quiescent current of the LT1614 is 1mA and the internal NPN power switch handles a 500mA current with a voltage drop of just 295mV. Better Regulation Than a Charge Pump 0.1Ω Effective Output Impedance – 5V at 200mA from a 5V Input 600kHz Fixed Frequency Operation Operates with VIN as Low as 1V 1mA Quiescent Current Low Shutdown Current: 10µA Low-Battery Detector Low VCESAT Switch: 295mV at 500mA U APPLICATIONS ■ ■ ■ ■ High frequency switching enables the use of small inductors and capacitors. Ceramic capacitors can be used in many applications, eliminating the need for bulky tantalum types. MR Head Bias LCD Bias GaAs FET Bias Positive-to-Negative Conversion The LT1614 is available in 8-lead MSOP or SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION 5V to – 5V Converter C3 1µF L1 22µH VIN 5V 5V to – 5V Converter Efficiency 90 L2 22µH C1 33µF 100k SHDN LT1614 VC NFB GND 69.8k D1 24.9k + + VOUT – 5V 200mA SW C2 33µF 1nF C1, C2: AVX TAJB336M010 C3: AVX 1206CY106 D1: MBR0520 L1, L2: MURATA LQH3C220 EFFICIENCY (%) 80 VIN 70 60 50 1614 TA01 40 3 100 10 30 LOAD CURRENT (mA) 300 1614 TA02 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1 LT1614 W W W AXI U U ABSOLUTE RATI GS VIN, SHDN, LBO Voltage ......................................... 12V SW Voltage ............................................... – 0.4V to 30V NFB Voltage ............................................................ – 3V VC Voltage ................................................................ 2V LBI Voltage ............................................ 0V ≤ VLBI ≤ 1V Current into FB Pin .............................................. ±1mA Junction Temperature ........................................... 125°C Operating Temperature Range LT1614C ................................................. 0°C to 70°C LT1614I ............................................. – 40°C to 85°C Extended Commercial Temperature Range (Note 1) .................. – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C U W U PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER ORDER PART NUMBER TOP VIEW TOP VIEW NFB VC SHDN GND 1 2 3 4 8 7 6 5 LBO LBI VIN SW MS8 PACKAGE 8-LEAD PLASTIC MSOP LT1614CMS8 MS8 PART MARKING TJMAX = 125°C, θJA = 160°C/W LTEJ NFB 1 8 LBO VC 2 7 LBI SHDN 3 6 VIN GND 4 5 SW LT1614CS8 LT1614IS8 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO 1614 1614I TJMAX = 125°C, θJA = 120°C/W Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN, TA = 25°C unless otherwise noted. PARAMETER CONDITIONS MIN Quiescent Current VSHDN = 0V Feedback Voltage NFB Pin Bias Current (Note 2) VNFB = –1.24V Reference Line Regulation 1V ≤ VIN ≤ 2V 2V ≤ VIN ≤ 6V Error Amp Transconductance 2 2 10 mA µA – 1.21 – 1.24 – 1.27 V – 2.5 – 4.5 –7 µA 0.6 0.3 1.1 0.8 %/V %/V 0.92 1 V 6 V ● ∆I = 5µA 16 µmhos 100 V/V ● 500 600 ● 73 70 80 80 % % 0.75 1.2 A Maximum Duty Cycle Switch Current Limit (Note 3) 1 5 UNITS ● Error Amp Voltage Gain Switching Frequency MAX ● Minimum Input Voltage Maximum Input Voltage TYP 750 kHz LT1614 ELECTRICAL CHARACTERISTICS Commercial Grade 0°C to 70°C. VIN = 1.5V, VSHDN = VIN, TA = 25°C unless otherwise noted. PARAMETER CONDITIONS TYP MAX UNITS Switch VCESAT ISW = 500mA (25°C, 0°C) ISW = 500mA (70°C) MIN 295 350 400 mV mV Shutdown Pin Current VSHDN = VIN VSHDN = 0V 10 –5 20 – 10 µA µA 200 210 215 mV mV LBI Threshold Voltage ● 190 185 LBO Output Low ISINK = 10µA 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V 0.01 0.1 µA LBI Input Bias Current (Note 4) VLBI = 150mV 10 50 nA Low-Battery Detector Gain 1MΩ Load 1000 Switch Leakage Current VSW = 5V 0.01 3 V/V TYP MAX 1 5 2 10 µA Industrial Grade – 40°C to 85°C. VIN = 1.5V, VSHDN = VIN unless otherwise noted. PARAMETER CONDITIONS MIN Quiescent Current VSHDN = 0V Feedback Voltage ● – 1.21 – 1.24 – 1.27 ● –2 UNITS mA µA V NFB Pin Bias Current (Note 2) VNFB = – 1.24V – 4.5 – 7.5 µA Reference Line Regulation 1V ≤ VIN ≤ 2V 2V ≤ VIN ≤ 6V 0.6 0.3 1.1 0.8 %/V %/V Minimum Input Voltage – 40°C 85°C 1.1 0.8 1.25 1.0 V V 6 V Maximum Input Voltage Error Amp Transconductance ● ∆I = 5µA µmhos 16 Error Amp Voltage Gain 100 Switching Frequency ● 500 600 Maximum Duty Cycle ● 70 80 Switch Current Limit (Note 3) 0.75 V/V 750 kHz % 1.2 A Switch VCESAT ISW = 500mA (– 40°C) ISW = 500mA (85°C) 250 330 350 400 mV mV Shutdown Pin Current VSHDN = VIN VSHDN = 0V 10 –5 20 – 10 µA µA 200 220 mV LBI Threshold Voltage ● 180 LBO Output Low ISINK = 10µA 0.1 0.25 V LBO Leakage Current VLBI = 250mV, VLBO = 5V 0.1 0.3 µA LBI Input Bias Current (Note 4) VLBI = 150mV 5 30 nA Low-Battery Detector Gain 1MΩ Load 1000 Switch Leakage Current VSW = 5V 0.01 The ● denotes specifications which apply over the full operating temperature range. Note 1: The LT1614C is guaranteed to meet specified performance from 0°C to 70°C and is designed, characterized and expected to meet these extended temperature limits, but is not tested at – 40°C and 85°C. The LT1614I is guaranteed to meet the extended temperature limits. V/V µA 3 Note 2: Bias current flows out of NFB pin. Note 3: Switch current limit guaranteed by design and/or correlation to static tests. Duty cycle affects current limit due to ramp generator. Note 4: Bias current flows out of LBI pin. 3 LT1614 U U U PIN FUNCTIONS NFB (Pin 1): Negative Feedback Pin. Reference voltage is – 1.24V. Connect resistive divider tap here. The suggested value for R2 is 24.9k. Set R1 and R2 according to: R1 = GND (Pin 4): Ground. Connect directly to local ground plane. SW (Pin 5): Switch Pin. Minimize trace area at this pin to keep EMI down. | VOUT | – 1.24 1.24 + 4.5 • 10 – 6 R2 VIN (Pin 6): Supply Pin. Must have 1µF ceramic bypass capacitor right at the pin, connected directly to ground. VC (Pin 2): Compensation Pin for Error Amplifier. Connect a series RC from this pin to ground. Typical values are 100kΩ and 1nF. Minimize trace area at VC. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and 700mV. Float this pin if not used. SHDN (Pin 3): Shutdown. Ground this pin to turn off switcher. Must be tied to VIN (or higher voltage) to enable switcher. Do not float the SHDN pin. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10µA. A 1MΩ pull-up is recommended. Float this pin if not used. W BLOCK DIAGRAM VIN 6 VIN R5 40k R6 40k + SHDN VC gm 2 ERROR AMPLIFIER + SHUTDOWN – Q1 Q2 ×10 LBI BIAS – R4 140k NFB LBO 8 A1 – 200mV A4 SW COMPARATOR – 1 VOUT + 7 ENABLE R3 30k RAMP GENERATOR R1 (EXTERNAL) + Σ + DRIVER FF A2 5 Q3 Q R + S + NFB R2 (EXTERNAL) 3 A=3 600kHz OSCILLATOR 0.15Ω – 4 GND 4 1614 BD LT1614 U U W U APPLICATIONS INFORMATION Shutdown Pin 3.3V R1 The LT1614 has a Shutdown pin (SHDN) that must be grounded to shut the device down or tied to a voltage equal or greater than VIN to operate. The shutdown circuit is shown in Figure 1. VIN LBI LT1614 1M + LBO R2 100k Note that allowing SHDN to float turns on both the startup current (Q2) and the shutdown current (Q3) for VIN > 2VBE. The LT1614 doesn’t know what to do in this situation and behaves erratically. SHDN voltage above VIN is allowed. This merely reverse-biases Q3’s base emitter junction, a benign condition. TO PROCESSOR – 200mV INTERNAL REFERENCE GND R1 = VLB – 200mV 2µA 1614 F02 Figure 2. Setting Low-Battery Detector Trip Point VIN 200k Q3 R2 400k SHDN VIN 2N3906 SHUTDOWN CURRENT LBO LT1614 VREF 200mV 200k 10k START-UP CURRENT LBI + GND 10µF 1614 F03 Q2 Figure 3. Accessing 200mV Reference Q1 1614 F01 Coupled Inductors Low-Battery Detector The LT1614’s low-battery detector is a simple PNP input gain stage with an open collector NPN output. The negative input of the gain stage is tied internally to a 200mV reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure 2 details hookup. R1 and R2 need only be low enough in value so that the bias current of the LBI pin doesn’t cause large errors. For R2, 100k is adequate. The 200mV reference can also be accessed as shown in Figure 3. The applications shown in this data sheet use two uncoupled inductors because the Murata units specified are small and inexpensive. This topology can also be used with a coupled inductor as shown in Figure 4. Be sure to get the phasing right. L1A 10µH VIN 5V + VIN C1 33µF 100k C3 1µF • • L1B 10µH VOUT – 5V 200mA SW SHDN LT1614 VC NFB GND 69.8k D1 24.9k + Figure 1. Shutdown Circuit C2 33µF 1nF C1, C2: AVX TAJB336M010 C3: AVX 1206CY106 D1: MBR0520 L1: COILTRONICS CTX10-1 1614 F04 Figure 4. 5V to – 5V Converter with Coupled Inductor 5 LT1614 U TYPICAL APPLICATION 5V to – 15V/80mA DC/DC Converter C1 1µF L1 22µH VIN + 100k VOUT –15V 80mA SW SHDN LT1614 NFB VC 22µF L2 22µH GND 255k D1 + VIN 5V 24.9k 10µF 25V 1nF C1: 25V, Y5V D1: MBR0520 L1, L2: MURATA LQH3C220 1614 TA05 5V to – 15V Converter Efficiency 80 EFFICIENCY (%) 75 70 65 60 55 50 1 10 LOAD CURRENT (mA) 100 1614 TA06 6 LT1614 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP (LTC DWG # 05-08-1660) 0.118 ± 0.004* (3.00 ± 0.102) 8 7 6 5 0.118 ± 0.004** (3.00 ± 0.102) 0.192 ± 0.004 (4.88 ± 0.10) 1 2 3 4 0.040 ± 0.006 (1.02 ± 0.15) 0.007 (0.18) 0.034 ± 0.004 (0.86 ± 0.102) 0° – 6° TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP 0.021 ± 0.006 (0.53 ± 0.015) 0.006 ± 0.004 (0.15 ± 0.102) MSOP (MS8) 1197 * DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP SO8 0996 7 LT1614 U TYPICAL APPLICATION 3.3V to – 3.1V/200mA DC/DC Converter C1 1µF L1 22µH VIN SHDN LT1614 VC + 22µF 100k VOUT – 3.1V 200mA SW 18.7k D1 FB GND 22µF + VIN 3.3V L2 22µH 12.7k 1nF C1: AVX1206CY106 D1: MBR0520 L1, L2: MURATA LQH3C220 1614 TA03 3.3V to – 3.1V Converter Efficiency 80 EFFICIENCY (%) 70 60 50 40 30 20 3 10 30 100 LOAD CURRENT (mA) 300 1614 TA04 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC®1174 High Efficiency Step-Down and Inverting DC/DC Converter Selectable IPEAK = 300mA or 600mA LT1307 Single Cell Micropower 600kHz PWM DC/DC Converter 3.3V at 75mA from 1 Cell, MSOP Package LT1308 Single Cell High Current Micropower 600kHz Boost Converter 5V at 1A from a Single Li-Ion Cell, SO-8 Package LT1316 Micropower Boost DC/DC Converter Programmable Peak Current Limit, MSOP Package LT1317 Micropower 600kHz PWM DC/DC Converter 2 Cells to 3.3V at 200mA, MSOP Package LTC1474 Low Quiescent Current High Efficiency DC/DC Converter IQ = 10µA, Programmable Peak Current Limit, MSOP LT1610 1.7MHz Single Cell Micropower DC/DC Converter 5V at 200mA from 3.3V, MSOP Package 8 Linear Technology Corporation 1614i LT/GP 0798 4K • PRINTED IN THE USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1998