LT1176/LT Step-Down Switching Regulator FEATURES APPLICATIONS DESCRIPTION TYPICAL APPLICATION

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Dominic Lang
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1 Step-Down Switching Reguator FEATURES n 1.2A Onboard Switch n 100kHz Switching Frequency n Exceent Dynamic Behavior n DIP and Surface Mount Packages n Ony 8mA Quiescent Current n Preset 5 Output Avaiabe n Operates Up to 35 Input n Micropower Shutdown Mode APPLICATIONS n Buck Converter with Output otage Range of 2.5 to 30 n Positive-to-Negative Converter n Negative Boost Converter n Mutipe Output Buck Converter DESCRIPTION The LT 1176 is a 1A monoithic bipoar switching reguator which requires ony a few externa parts for norma operation. The power switch, a osciator and contro circuitry and a current imit components are incuded on the chip. The topoogy is a cassic positive buck configuration but severa design innovations aows this device to be used as a positive-to-negative converter, a negative boost converter, and as a fyback converter. The switch output is specified to swing beow ground. The LT1176 uses a true anaog mutipier in the feedback oop. This makes the device respond neary instantaneousy to input votage fuctuations and makes oop gain independent of input votage. As a resut, dynamic behavior of the reguator is significanty improved over previous designs. On-chip puse by puse current imiting makes the LT1176 neary bust proof for output overoads or shorts. The input votage range as a buck converter is 8 to 35, but a sef boot feature aows input votages as ow as 5 in the inverting and boost configurations. The LT1176 is avaiabe in a ow cost 8-ead DIP package with frequency preset at 100kHz and current imit at 1.7A. An adjustabe output is offered as we as a preset 5 version. For further design detais and appication hep, see the LT1074/LT1076 data sheet and Appication Note 44. L, LT, LTC, LTM, Linear Technoogy, SwitcherCAD and the Linear ogo are registered trademarks of Linear Technoogy Corporation. A other trademarks are the property of their respective owners. TYPICAL APPLICATION Basic 5 Positive Buck Converter 5 Buck Converter Efficiency 10 T0 35 IN SW L1* 100µH 5, 0.8A 90 L = 100µH ON MAGNETICS I. SIZE T-50 KOOL Mµ CORE C3 100µF LT SENSE C R3 2.7k C2 0.01µF 1N5819 C1 470µF 25 EFFICIEY (%) IN = 10 IN = 20 *COILTRONICS # TA01 PULSE ENGINEERING, I. #PE HURRICANE #HL-AG210LL THESE ARE LOW COST POWDERED IRON CORES. OPTIMUM EFFICIEY AND SMALLEST SIZE IS OBTAINED BY USING A LOW LOSS CORE SUCH AS MAGNETICS I. KOOL Mµ. SEE EFFICIEY GRAPH LOAD CURRENT (A) TA02 1

2 ABSOLUTE MAXIMUM RATINGS (Note 1) Input otage...38 Switch otage with Respect to Input otage...50 Switch otage with Respect to Ground Pin ( SW Negative) (Note 7)...20 Feedback Pin otage... 2, 10 Shutdown Pin otage (Not to Exceed IN )...35 Status Pin otage (Current Must Be Limited to 5mA When Status Pin Switches ON)...30 I LIM Pin otage (Forced) Maximum Operating Ambient Temperature Range LT1176C/LT1176C C to 70 C Maximum Operating Junction Temperature Range LT1176C/LT1176C C to 125 C Storage Temperature Range C to 150 C Lead Temperature (Sodering, 10 sec) C *These therma resistance numbers are for typica mounting technique. Lower therma resistance can be obtained with arge copper ands, therma gues or heat sinks. PIN CONFIGURATION TOP IEW IN 1 20 SW TOP IEW I LIM C IN 1 8 SW 4 17 I LIM 2 7 C STATUS 6 15 FB/SENSE N8 PACKAGE 8-LEAD PLASTIC DIP T JMAX = 125 C, θ JA = 90 C/W FB/SENSE STATUS SW PACKAGE 20-LEAD PLASTIC SOL T JMAX = 125 C, θ JA = 50 C/W ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT1176CN8#PBF LT1176CN8 8-Lead Pastic DIP 0 C to 125 C LT1176CN8-5#PBF LT1176CN8-5 8-Lead Pastic DIP 0 C to 125 C LT1176CSW#PBF LT1176CSW#TRPBF LT1176CSW 20-Lead Pastic SOL 0 C to 125 C LT1176CSW-5#PBF LT1176CSW-5#TRPBF LT1176CSW-5 20-Lead Pastic SOL 0 C to 125 C Consut LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a abe on the shipping container. For more information on ead free part marking, go to: For more information on tape and ree specifications, go to: 2

3 ELECTRICAL CHARACTERISTICS LT1176/LT The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = 25 C. T J = 25 C, IN 25, uness otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Switch ON otage (Note 2) I SW = 0.2A I SW = 1A Switch OFF Leakage IN = 25, SW = 0 IN = MAX, SW = 0 (Note 8) Suppy Current (Note 3) FB = 2.5, IN 35 SHDN = 0.1 (Device Shutdown) (Note 9) Minimum Suppy otage Norma Mode Startup Mode (Note 4) Switch Current Limit (Note 5) I LIM Open R LIM = 10k (Note 6) R LIM = 7k (Note 6) ma 2.2 A A A Maximum Duty Cyce % Switching Frequency khz khz FB = 0 Through 2k (Note 5) (LT1176) SENSE = 0 (Note 5) (LT1176-5) khz khz Switching Frequency Line Reguation 8 IN MAX (Note 8) %/ Error Ampifier otage Gain (Note 10) 1 C / Error Ampifier Transconductance (Note 10) µmho Error Ampifier Source and Sink Current Source ( FB = 2 or SENSE = 4) Sink ( FB = 2.5 or SENSE = 5.5) Feedback Pin Bias Current (LT1176) FB = REF Reference otage (LT1176) C = Reference otage Toerance (LT1176) REF (Nomina) = 2.21 A Conditions of Input otage, Output otage, Temperature and Load Current Sense otage (LT1176-5) C = Sense otage Toerance (LT1176-5) OUT (Nomina) = 5 A Conditions of Input otage, ±0.5 ±0.1 ±2 ±3 % % Temperature and Load Current Sense Pin Divider Resistance (LT1176-5) kω Output otage Line Reguation 8 IN MAX (Note 8) %/ C otage at 0% Duty Cyce 1.5 Overtemperature 4.0 m/ C Mutipier Reference otage 24 Shutdown Pin Current SHDN = 5 SHDN THRESHOLD (@ 2.5) Shutdown Threshods Switch Duty Cyce = 0 Fuy Shutdown Status Window As a Percent of Output otage ±4 ±5 ±6 % Status High Leve I STATUS = 10 Sourcing ±0.5 ± ±2 ± ma % % 3

4 ELECTRICAL CHARACTERISTICS The denotes the specifications which appy over the fu operating temperature range, otherwise specifications are at T A = 25 C. T J = 25 C, IN 25, uness otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Status Low Leve I STATUS = 1.6mA Sinking Status Deay Time 9 µs Status Minimum Width 30 µs Note 1: Stresses beyond those isted under Absoute Maximum Ratings may cause permanent damage to the device. Exposure to any Absoute Maximum Rating condition for extended periods may affect device reiabiity and ifetime. Note 2: To cacuate maximum switch ON votage at current between ow and high conditions, a inear interpoation may be used. Note 3: A feedback pin votage ( FB ) of 2.5 forces the C pin to its ow camp eve and the switch duty cyce to zero. This approximates the zero oad condition where duty cyce approaches zero. The LT has SENSE = 5.5. Note 4: Tota votage from IN pin to ground pin must be 8 after start-up for proper reguation. Note 5: Switch frequency is internay scaed down when the feedback pin votage is ess than 1.3 to avoid extremey short switch-on times. During testing, FB or SENSE is adjusted to give a minimum switch-on time of 1µs. Note 6: I LM = (R LIM 1k)/7.65k Note 7: Switch to input votage imitation must aso be observed. Note 8: MAX = 35 Note 9: Does not incude switch eakage. Note 10: Error ampifier votage gain and transconductance are specified reative to the interna feedback node. To cacuate gain and transconductance from the sense pin (Output) to the C pin on the LT1176-5, mutipy by Appication Hints Athough the LT1176 has a peak switch rating of 1.2A and a maximum duty cyce of 85%, it must be used cautiousy in appications which require high switch current and high duty cyce simutaneousy, to avoid excessive chip temperature. Therma resistance is 90 C/W for the 8-pin DIP package and 50 C/W for the 20-pin SO. This imits continuous chip power dissipation to the 0.5W to 1W range. These numbers assume typica mounting techniques. Extra or thick copper connected to the eads can reduce therma resistance. Bonding the package to the board or using a cip stye heat sink can aso hep. The foowing formuas wi give chip power dissipation and peak switch current for the standard buck converter. Note that surges ess than 30 seconds do not need to be considered from a therma standpoint, but for proper reguation, they must not resut in peak switch currents exceeding the 1.2A imit. Power = I LOAD ( OUT / IN ) IN [7mA 3mA ( OUT / IN ) (I LOAD )] I PEAK = I LOAD(PEAK) [ OUT ( IN OUT )]/2E 5 ( IN )(L) Exampe: IN = 15, OUT = 5, I LOAD = 0.5A Continuous, 0.8A Peak, L = 100µH Power (I LOAD = 0.5A) = 0.38W I PEAK (I LOAD = 0.8A) = 0.97A Where component size or height is critica, we suggest using soid tantaum capacitors (singy or in parae), but be sure to use units rated for switching appications. Coitronics is a good source for ow profie surface mount inductors and AX makes high quaity surface mount tantaum capacitors. For further hep, use Appication Notes 19 and 44,LTC s SwitcherCAD computer design program, and our knowedgeabe appication department. 4

5 BLOCK DIAGRAM LT1176/LT INPUT SUPPLY µpower 6 REGULATOR AND BIAS 6 TO ALL CIRCUITRY Ω 2.35 CURRENT LIMIT CURRENT LIMIT COMP 0.16Ω I LIM C k OUTPUT OLTAGE MONITOR STATUS 2.21 A1 ERROR AMP X FREQ SHIFT 100kHz OSCILLATOR SY IN Z ANALOG MULTIPLIER XYZ Y 3 P-P C1 R R/S S Q LATCH R PULSE WIDTH COMPARATOR G1 400Ω SWITCH OUTPUT ( SW ) FB/SENSE 2.8k 2.2k* C 24 (EQUIALENT) BD *CONNECTED ON 5 ERSION ONLY 5

6 PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow.300 Inch) (Reference LTC DWG # ).400* (10.160) MAX ±.015* (6.477 ± 0.381) ( ) ( ).130 ±.005 (3.302 ± 0.127) ( ) ( ).065 (1.651) TYP.100 (2.54) BSC NOTE: IHES 1. DIMENSIONS ARE MILLIMETERS *THESE DIMENSIONS DO NOT ILUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED.010 IH (0.254mm).120 (3.048) MIN.018 ±.003 (0.457 ± 0.076).020 (0.508) MIN N

7 REISION HISTORY RE DATE DESCRIPTION PAGE NUMBER A 01/11 Corrected Typica Appication Updated part markings in Order Information Revised Eectrica Characteristics Updated Package Description B 2/11 Revised Shutdown Pin Current in Eectrica Characteristics 3 Information furnished by Linear Technoogy Corporation is beieved to be accurate and reiabe. However, no responsibiity is assumed for its use. Linear Technoogy Corporation makes no representation that the interconnection of its circuits as described herein wi not infringe on existing patent rights. 7

8 PACKAGE DESCRIPTION SW Package 20-Lead Pastic Sma Outine (Wide.300 Inch) (Reference LTC DWG # ) TYP N.050 BSC ( ) NOTE MIN N NOTE ( ) N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT.005 (0.127) RAD MIN ( ) NOTE ( ) 0 8 TYP ( ) ( ) ( ) NOTE 3 (1.270) BSC ( ) ( ) NOTE: TYP IHES 1. DIMENSIONS IN (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. PIN 1 IDENT, NOTCH ON TOP AND CAITIES 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 ILUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED.006" (0.15mm) ( ) S20 (WIDE) LT 0211 RE B PRINTED IN USA Linear Technoogy Corporation 1630 McCarthy Bvd., Mipitas, CA (408) FAX: (408) LINEAR TECHNOLOGY CORPORATION 1993

FEATURES APPLICATIONS TYPICAL APPLICATION

FEATURES APPLICATIONS TYPICAL APPLICATION FEATURES n Reguates Whie Sourcing or Sinking Current n Provides Termination for up to 27 SCSI Lines n μa Quiescent Current n Utraow Power Shutdown Mode n Current Limit and Therma Shutdown Protection n