LT1176/LT1176-5 Step-Down Switching Regulator FEATURES n n n n n n n n and all current limit components are included on the chip. The topology is a classic positive buck configuration but several design innovations allows this device to be used as a positive-to-negative converter, a negative boost converter, and as a flyback converter. The switch output is specified to swing below ground. 1.2A Onboard Switch 100kHz Switching Frequency Excellent Dynamic Behavior DIP and Surface Mount Packages Only 8mA Quiescent Current Preset 5V Output Available Operates Up to 35V Input Micropower Shutdown Mode The LT1176 uses a true analog multiplier in the feedback loop. This makes the device respond nearly instantaneously to input voltage fluctuations and makes loop gain independent of input voltage. As a result, dynamic behavior of the regulator is significantly improved over previous designs. APPLICATIONS n n n n On-chip pulse by pulse current limiting makes the LT1176 nearly bust proof for output overloads or shorts. The input voltage range as a buck converter is 8V to 35V, but a self boot feature allows input voltages as low as 5V in the inverting and boost configurations. Buck Converter with Output Voltage Range of 2.5V to 30V Positive-to-Negative Converter Negative Boost Converter Multiple Output Buck Converter DESCRIPTION The LT®1176 is a 1A monolithic bipolar switching regulator which requires only a few external parts for normal operation. The power switch, all oscillator and control circuitry The LT1176 is available in a low cost 8-lead DIP package with frequency preset at 100kHz and current limit at 1.7A. An adjustable output is offered as well as a preset 5V version. For further design details and application help, see the LT1074/LT1076 data sheet and Application Note 44. L, LT, LTC, LTM, Linear Technology, SwitcherCAD and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Basic 5V Positive Buck Converter 5V Buck Converter Efficiency 90 L1* 100µH LT1176-5 GND + 1N5819 SENSE VC R3 2.7k C3 100µF 5V, 0.8A VSW VIN + C1 470µF 25V C2 0.01µF *COILTRONICS #100-1-52 11765 TA01 PULSE ENGINEERING, INC. #PE-92102 HURRICANE #HL-AG210LL THESE ARE LOW COST POWDERED IRON CORES. OPTIMUM EFFICIENCY AND SMALLEST SIZE IS OBTAINED BY USING A LOW LOSS CORE SUCH AS MAGNETICS INC. KOOL Mµ. SEE EFFICIENCY GRAPH. EFFICIENCY (%) 10V T0 35V 80 L = 100µH ON MAGNETICS INC. SIZE T-50 KOOL Mµ CORE VIN = 10V VIN = 20V 70 60 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 11765 TA02 11765fb 1 LT1176/LT1176-5 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage..............................................................38V Switch Voltage with Respect to Input Voltage...........50V Switch Voltage with Respect to Ground Pin (VSW Negative) (Note 7).............................................20V Feedback Pin Voltage......................................... –2V, 10V Shutdown Pin Voltage (Not to Exceed VIN)................35V Status Pin Voltage (Current Must Be Limited to 5mA When Status Pin Switches ON).........................................................30V ILIM Pin Voltage (Forced)..........................................5.5V Maximum Operating Ambient Temperature Range LT1176C/LT1176C-5.................................. 0°C to 70°C Maximum Operating Junction Temperature Range LT1176C/LT1176C-5................................ 0°C to 125°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec).................... 300°C *These thermal resistance numbers are for typical mounting technique. Lower thermal resistance can be obtained with large copper lands, thermal glues or heat sinks. PIN CONFIGURATION TOP VIEW TOP VIEW VIN 1 20 VSW NC 2 19 NC ILIM 3 18 VC VIN 1 8 VSW GND 4 17 GND ILIM 2 7 VC GND 5 16 GND GND 3 6 STATUS GND 6 15 GND FB/SENSE 4 5 SHUTDOWN GND 7 14 GND NC 8 N8 PACKAGE 8-LEAD PLASTIC DIP 13 STATUS FB/SENSE 9 TJMAX = 125°C, θJA = 90°C/W 12 SHUTDOWN NC 10 11 NC SW PACKAGE 20-LEAD PLASTIC SOL TJMAX = 125°C, θJA = 50°C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1176CN8#PBF LT1176CN8 8-Lead Plastic DIP 0°C to 125°C LT1176CN8-5#PBF LT1176CN8-5 8-Lead Plastic DIP 0°C to 125°C LT1176CSW#PBF LT1176CSW#TRPBF LT1176CSW 20-Lead Plastic SOL 0°C to 125°C LT1176CSW-5#PBF LT1176CSW-5#TRPBF LT1176CSW-5 20-Lead Plastic SOL 0°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/ 11765fb 2 LT1176/LT1176-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. TJ = 25°C, VIN 25V, unless otherwise noted. PARAMETER CONDITIONS Switch ON Voltage (Note 2) ISW = 0.2A ISW = 1A Switch OFF Leakage VIN = 25V, VSW = 0 VIN = VMAX, VSW = 0 (Note 8) Supply Current (Note 3) VFB = 2.5V, VIN ≤ 35V VSHDN = 0.1V (Device Shutdown) (Note 9) l l Minimum Supply Voltage Normal Mode Startup Mode (Note 4) l l Switch Current Limit (Note 5) ILIM Open RLIM = 10k (Note 6) RLIM = 7k (Note 6) l Maximum Duty Cycle MIN Error Amplifier Voltage Gain (Note 10) 1V ≤ VC ≤ 4V 150 250 µA µA 7.5 140.0 10 300 mA µA 7.3 3.5 8.0 4.8 V V 1.2 1.7 1.2 0.8 2.2 A A A l 85 90 90 85 100 l % 110 120 kHz kHz kHz kHz 0.1 %/V 2000 Error Amplifier Source and Sink Current Source (VFB = 2V or VSENSE = 4V) Sink (VFB = 2.5V or VSENSE = 5.5V) Feedback Pin Bias Current (LT1176) VFB = VREF l Reference Voltage (LT1176) VC = 2V l Reference Voltage Tolerance (LT1176) VREF (Nominal) = 2.21V All Conditions of Input Voltage, Output Voltage, Temperature and Load Current l Sense Voltage (LT1176-5) VC = 2V l Sense Voltage Tolerance (LT1176-5) VOUT (Nominal) = 5V All Conditions of Input Voltage, Temperature and Load Current l Sense Pin Divider Resistance (LT1176-5) VC Voltage at 0% Duty Cycle 20 20 0.03 l Error Amplifier Transconductance (Note 10) Output Voltage Line Regulation UNITS V V VFB = 0V Through 2k (Note 5) (LT1176) VSENSE = 0V (Note 5) (LT1176-5) 8V ≤ VIN ≤ VMAX (Note 8) MAX 1.1 1.4 Switching Frequency Switching Frequency Line Regulation TYP l l V/V 3700 5000 8000 µmho 100.0 0.7 140 1.0 225.0 1.6 µA mA 0.5 2 µA 2.155 4.85 3 2.21 2.265 V ±0.5 ±1.0 ±2 ±3 % % 5 5.15 V ±0.5 ±0.1 ±2 ±3 % % 5 8 kΩ 0.02 %/V 8V ≤ VIN ≤ VMAX (Note 8) l 0.005 Overtemperature l 1.5 –4.0 Multiplier Reference Voltage V mV/°C 24 V Shutdown Pin Current VSHDN = 5V VSHDN ≤ VTHRESHOLD (@ 2.5V) l l 5 10 20 50 µA µA Shutdown Thresholds Switch Duty Cycle = 0 Fully Shutdown l l 2.2 0.1 2.45 0.30 2.7 0.5 V V Status Window As a Percent of Output Voltage ±4 ±5 ±6 % Status High Level ISTATUS = 10µA Sourcing 3.5 4.5 5.0 V l 11765fb 3 LT1176/LT1176-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. TJ = 25°C, VIN 25V, unless otherwise noted. PARAMETER CONDITIONS Status Low Level ISTATUS = 1.6mA Sinking MIN l TYP MAX 0.25 0.4 UNITS V Status Delay Time 9 µs Status Minimum Width 30 µs Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: To calculate maximum switch ON voltage at current between low and high conditions, a linear interpolation may be used. Note 3: A feedback pin voltage (VFB) of 2.5V forces the VC pin to its low clamp level and the switch duty cycle to zero. This approximates the zero load condition where duty cycle approaches zero. The LT1176-5 has VSENSE = 5.5V. Note 4: Total voltage from VIN pin to ground pin must be ≥ 8V after start-up for proper regulation. Application Hints Although the LT1176 has a peak switch rating of 1.2A and a maximum duty cycle of 85%, it must be used cautiously in applications which require high switch current and high duty cycle simultaneously, to avoid excessive chip temperature. Thermal resistance is 90°C/W for the 8-pin DIP package and 50°C/W for the 20-pin SO. This limits continuous chip power dissipation to the 0.5W to 1W range. These numbers assume typical mounting techniques. Extra or thick copper connected to the leads can reduce thermal resistance. Bonding the package to the board or using a clip style heat sink can also help. The following formulas will give chip power dissipation and peak switch current for the standard buck converter. Note that surges less than 30 seconds do not need to be considered from a thermal standpoint, but for proper regulation, they must not result in peak switch currents exceeding the 1.2A limit. Note 5: Switch frequency is internally scaled down when the feedback pin voltage is less than 1.3V to avoid extremely short switch-on times. During testing, VFB or VSENSE is adjusted to give a minimum switch-on time of 1µs. Note 6: ILM = (RLIM – 1k)/7.65k Note 7: Switch to input voltage limitation must also be observed. Note 8: VMAX = 35V Note 9: Does not include switch leakage. Note 10: Error amplifier voltage gain and transconductance are specified relative to the internal feedback node. To calculate gain and transconductance from the sense pin (Output) to the VC pin on the LT1176-5, multiply by 0.44. Power = ILOAD(VOUT/VIN) + VIN [7mA + 3mA (VOUT/VIN) + 0.012 (ILOAD)] IPEAK = ILOAD(PEAK) + [VOUT(VIN – VOUT)]/2E5(VIN)(L) Example: VIN = 15V, VOUT = 5V, ILOAD = 0.5A Continuous, 0.8A Peak, L = 100µH Power (ILOAD = 0.5A) = 0.38W IPEAK (ILOAD = 0.8A) = 0.97A Where component size or height is critical, we suggest using solid tantalum capacitors (singly or in parallel), but be sure to use units rated for switching applications. Coiltronics is a good source for low profile surface mount inductors and AVX makes high quality surface mount tantalum capacitors. For further help, use Application Notes 19 and 44,LTC’s SwitcherCAD® computer design program, and our knowledgeable application department. 11765fb 4 LT1176/LT1176-5 BLOCK DIAGRAM INPUT SUPPLY 10µA 0.3V 320µA + 6V REGULATOR AND BIAS µPOWER SHUTDOWN – 2.35V 6V TO ALL CIRCUITRY 500Ω CURRENT LIMIT SHUTDOWN + CURRENT LIMIT COMP 0.16Ω + C2 – – ILIM 4.5V SHUTDOWN 10k FREQ SHIFT 100kHz OSCILLATOR SYNC OUTPUT VOLTAGE MONITOR 3VP-P R R/S Q LATCH R G1 VIN Z + STATUS 2.21V FB/SENSE S 2.8k ANALOG X MULTIPLIER XYZ A1 ERROR AMP – 2.2k* Y 400Ω + C1 – PULSE WIDTH COMPARATOR SWITCH OUTPUT (VSW) 11765 BD VC 24V (EQUIVALENT) *CONNECTED ON 5V VERSION ONLY 11765fb 5 LT1176/LT1176-5 PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .400* (10.160) MAX 8 7 6 5 1 2 3 4 .255 ± .015* (6.477 ± 0.381) .300 – .325 (7.620 – 8.255) .008 – .015 (0.203 – 0.381) ( +.035 .325 –.015 8.255 +0.889 –0.381 ) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .100 (2.54) BSC .130 ± .005 (3.302 ± 0.127) .120 (3.048) .020 MIN (0.508) MIN .018 ± .003 (0.457 ± 0.076) N8 1002 NOTE: 1. DIMENSIONS ARE INCHES MILLIMETERS *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm) 11765fb 6 LT1176/LT1176-5 REVISION HISTORY REV DATE DESCRIPTION A 01/11 Corrected Typical Application 1 Updated part markings in Order Information 2 Revised Electrical Characteristics 3 Updated Package Description 8 Revised Shutdown Pin Current in Electrical Characteristics 3 B 2/11 PAGE NUMBER 11765fb 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. 7 LT1176/LT1176-5 PACKAGE DESCRIPTION SW Package 20-Lead Plastic Small Outline (Wide .300 Inch) (Reference LTC DWG # 05-08-1620) .050 BSC .045 .005 .030 .005 TYP .496 – .512 (12.598 – 13.005) NOTE 4 N 20 18 17 16 15 14 13 12 11 N .325 .005 .420 MIN 19 .394 – .419 (10.007 – 10.643) NOTE 3 1 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT .005 (0.127) RAD MIN .009 – .013 (0.229 – 0.330) NOTE: 1. DIMENSIONS IN .291 – .299 (7.391 – 7.595) NOTE 4 .010 – .029 ¥ 45∞ (0.254 – 0.737) 1 2 3 4 5 6 7 8 .093 – .104 (2.362 – 2.642) 9 10 .037 – .045 (0.940 – 1.143) 0 – 8 TYP .050 (1.270) BSC NOTE 3 .014 – .019 (0.356 – 0.482) TYP .016 – .050 (0.406 – 1.270) .004 – .012 (0.102 – 0.305) S20 (WIDE) 0502 INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS 4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 11765fb 8 Linear Technology Corporation LT 0211 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 1993