LT1176/LT1176-5 Step-Down Switching Regulator and all current limit components are included on the chip. FEATURES The topology is a classic positive buck configuration but n 1.2A Onboard Switch several design innovations allows this device to be used as n 100kHz Switching Frequency a positive-to-negative converter, a negative boost converter, n Excellent Dynamic Behavior and as a flyback converter. The switch output is specified n DIP and Surface Mount Packages to swing below ground. n Only 8mA Quiescent Current The LT1176 uses a true analog multiplier in the feedback n Preset 5V Output Available loop. This makes the device respond nearly instantaneously n Operates Up to 35V Input to input voltage fluctuations and makes loop gain indepen- n Micropower Shutdown Mode dent of input voltage. As a result, dynamic behavior of the regulator is significantly improved over previous designs. APPLICATIONS On-chip pulse by pulse current limiting makes the LT1176 nearly bust proof for output overloads or shorts. The input n Buck Converter with Output Voltage Range of voltage range as a buck converter is 8V to 35V, but a self 2.5V to 30V boot feature allows input voltages as low as 5V in the n Positive-to-Negative Converter inverting and boost configurations. n Negative Boost Converter n Multiple Output Buck Converter 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 ver- DESCRIPTION sion. For further design details and application help, see The LT 1176 is a 1A monolithic bipolar switching regulator the LT1074/LT1076 data sheet and Application Note 44. which requires only a few external parts for normal opera- 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 tion. The power switch, all oscillator and control circuitry respective owners. TYPICAL APPLICATION Basic 5V Positive Buck Converter 5V Buck Converter Efficiency 90 L1* L = 100H ON MAGNETICS INC. 100H SIZE T-50 KOOL M CORE 10V T0 35V V V 5V, 0.8A IN SW LT1176-5 V = 10V IN 1N5819 80 SENSE V = 20V IN GND V C + C1 470F R3 25V 2.7k 70 + C3 C2 100F 0.01F *COILTRONICS 100-1-52 60 11765 TA01 PULSE ENGINEERING, INC. PE-92102 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 HURRICANE HL-AG210LL LOAD CURRENT (A) THESE ARE LOW COST POWDERED IRON CORES. OPTIMUM EFFICIENCY 11765 TA02 AND SMALLEST SIZE IS OBTAINED BY USING A LOW LOSS CORE SUCH AS MAGNETICS INC. KOOL M. SEE EFFICIENCY GRAPH. 11765fb 1 EFFICIENCY (%)LT1176/LT1176-5 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage .............................................................38V I Pin Voltage (Forced) .........................................5.5V LIM Switch Voltage with Respect to Input Voltage...........50V Maximum Operating Ambient Temperature Range Switch Voltage with Respect to Ground Pin LT1176C/LT1176C-5 ................................. 0C to 70C (V Negative) (Note 7) ............................................20V Maximum Operating Junction Temperature Range SW Feedback Pin Voltage ........................................2V, 10V LT1176C/LT1176C-5 ............................... 0C to 125C Shutdown Pin Voltage (Not to Exceed V ) ...............35V Storage Temperature Range .................. 65C to 150C IN Status Pin Voltage Lead Temperature (Soldering, 10 sec) ...................300C (Current Must Be Limited to 5mA When Status Pin *These thermal resistance numbers are for typical mounting technique. Lower thermal resistance can be obtained with large copper lands, thermal glues or heat sinks. Switches ON) ........................................................30V PIN CONFIGURATION TOP VIEW V 1 20 V IN SW NC 2 19 NC TOP VIEW I 3 18 V LIM C V 1 8 V GND 4 17 GND IN SW I 2 7 V GND 5 16 GND LIM C GND 6 15 GND GND 3 6 STATUS GND 7 14 GND FB/SENSE 4 5 SHUTDOWN NC 8 13 STATUS N8 PACKAGE FB/SENSE 9 12 SHUTDOWN 8-LEAD PLASTIC DIP T = 125C, = 90C/W NC 10 11 NC JMAX JA SW PACKAGE 20-LEAD PLASTIC SOL T = 125C, = 50C/W JMAX JA ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1176CN8 PBF LT1176CN8 8-Lead Plastic DIP 0C to 125C LT1176CN8-5 PBF LT1176CN8-5 8-Lead Plastic DIP 0C to 125C LT1176CSW PBF LT1176CSW TRPBF LT1176CSW 20-Lead Plastic SOL 0C to 125C LT1176CSW-5 PBF LT1176CSW-5 TRPBF LT1176CSW-5 20-Lead Plastic SOL 0C to 125C 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: