LT1176/LT1176-5 Step-Down Switching Regulator FEATURES ■ ■ ■ ■ ■ ■ ■ ■ tion. The power switch, all oscillator and control circuitry, 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 On-Board 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. UO APPLICATI ■ ■ ■ ■ S 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 selfboot 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 Mulitple Output Buck Converter U DESCRIPTIO The LT1176 is a 1A monolithic bipolar switching regulator which requires only a few external parts for normal opera- 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. UO TYPICAL APPLICATI 5V Buck Converter Efficiency Basic 5V Positive Buck Converter 90 L1* 100µH LT1176-5 GND + VIN = 10V 1N5819 SENSE VC R3 2.7k C3 100µF L = 100µH ON MAGNETICS INC. SIZE T-50 KOOL Mµ CORE 5V, 0.8A VSW VIN + C1 470µF 25V EFFICIENCY (%) 10V T0 35V 80 VIN = 20V 70 C2 0.01µF *COILTRONICS #100-1-52 LT1176/76-5 • 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. 60 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) LT1176/76-5 • TA02 1 LT1176/LT1176-5 U U RATI GS W W W W AXI U U ABSOLUTE PACKAGE/ORDER I FOR ATIO Input Voltage .......................................................... 38V Switch Voltage With Respect to Input Voltage ........ 50V Switch Voltage With Respect to Ground Pin (VSW Negative) (Note 6) ......................................... 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 TOP VIEW 8 VSW ILIM 2 7 VC GND 3 6 STATUS FB/SENSE 4 5 SHUTDOWN LT1176CN8 LT1176CN8-5 N8 PACKAGE 8-LEAD PLASTIC DIP TJ MAX = 125°C, θJA = 90°C/ W* TOP VIEW VIN 1 20 VSW NC 2 19 NC ILIM 3 18 VC GND 4 17 GND GND 5 16 GND GND 6 15 GND GND 7 14 GND NC 8 *These thermal resistance numbers are for typical mounting technique. Lower thermal resistance can be obtained with large copper lands, thermal glues or heatsinks. ORDER PART NUMBER VIN 1 ORDER PART NUMBER LT1176CS LT1176CS-5 13 STATUS FB/SENSE 9 12 SHUTDOWN NC 10 11 NC S PACKAGE 20-LEAD PLASTIC SOL TJMAX = 125 °C, θJA = 50°C/ W* ELECTRICAL CHARACTERISTICS TJ = 25°C, VIN = 25V, unless otherwise noted PARAMETER CONDITIONS Switch “ON” Voltage (Note 1) ISW = 0.2A ISW = 1A Switch “OFF” Leakage VIN = 25V, VSW = 0 VIN = VMAX, VSW = 0 (Note 7) Supply Current (Note 2) VFB = 2.5V, VIN ≤ 35V VSHDN = 0.1V (Device Shutdown) (Note 8) ● ● Minimum Supply Voltage Normal Mode Startup Mode (Note 3) ● ● Switch Current Limit (Note 4) ILIM Open RLIM = 10k (Note 5) RLIM = 7k (Note 5) ● Maximum Duty Cycle MIN 8V ≤ VIN ≤ VMAX (Note 7) 1V ≤ VC ≤ 4V Error Amplifier Transconductance (Note 9) Error Amplifier Source and Sink Current 2 Source (VFB = 2V or VSENSE = 4V) Sink (VFB = 2.5V or VSENSE = 5.5V) UNITS V V 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 ● 85 90 90 85 100 ● VFB = 0V Through 2k (Note 4) (LT1176) VSENSE = 0V (Note 4) (LT1176-5) Error Amplifier Voltage Gain (Note 9) MAX 1.1 1.4 Switching Frequency Switching Frequency Line Regulation TYP ● ● % 110 120 kHz kHz kHz kHz 0.1 %/ V 20 20 0.03 ● 2000 V/ V 3700 5000 8000 µmho 100.0 0.7 140.0 1.0 225.0 1.6 µA mA LT1176/LT1176-5 ELECTRICAL CHARACTERISTICS TJ = 25°C, VIN = 25V, unless otherwise noted PARAMETER CONDITIONS Feedback Pin Bias Current (LT1176) VFB = VREF ● MIN Reference Voltage (LT1176) VC = 2V ● Reference Voltage Tolerance (LT1176) VREF (Nominal) = 2.21V All Conditions of Input Voltage, Output Voltage, Temperature and Load Current ● Sense Voltage (LT1176-5) VC = 2V ● Sense Voltage Tolerance (LT1176-5) VOUT (Nominal) = 5V All Conditions of Input Voltage, Temperature and Load Current ● Output Voltage Line Regulation 2 UNITS µA 2.21 2.265 V ±1.5 ±2.5 % % 5 5.15 V ±0.5 ±1.0 ±2 ±3 % % 5 8 kΩ ● 0.005 0.02 %/ V Over Temperature ● 1.5 – 4.0 VSHDN = 5V ● 5 10 50 20 µA µA ● ● 2.2 0.1 2.45 0.30 2.7 0.5 V V ±4 ±5 ±6 % 4.5 5.0 V 0.25 0.4 V 4.85 3 8V ≤ VIN ≤ VMAX (Note 7) VC Voltage at 0% Duty Cycle Multiplier Reference Voltage Shutdown Pin Current VSHDN ≤ VTHRESHOLD (≅ 2.5V) MAX 0.5 ±0.5 ±1.0 Sense Pin Divider Resistance (LT1176-5) 2.155 TYP V mV/°C 24 ● Shutdown Thresholds Switch Duty Cycle = 0 Fully Shut Down Status Window As a Percent of Output Voltage Status High Level ISTATUS = 10µA Sourcing ● Status Low Level ISTATUS = 1.6mA Sinking ● 3.5 V Status Delay Time 9 µs Status Minimum Width 30 µs The ● denotes specifications which apply over the full operating temperature range. Note 1: To calculate maximum switch “ON” voltage at current between low and high conditions, a linear interpolation may be used. Note 2: 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 3: Total voltage from VIN pin to ground pin must be ≥8V after startup for proper regulation. Note 4: 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 5: ILM = (RLIM – 1k)/ 7.65k Note 6: Switch to input voltage limitation must also be observed. Note 7: VMAX = 35V Note 8: Does not include switch leakage. Note 9: 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. Application Hints Power = ILOAD (VOUT/VIN) + VIN [7mA + 3mA (VOUT/VIN) + 0.012 (ILOAD)] 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 heatsink 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. 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. 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. 3 LT1176/LT1176-5 W BLOCK DIAGRA 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 S R R/S Q LATCH R G1 3VP-P VIN + STATUS 2.21V – 2.8k C1 ANALOG X MULTIPLIER XYZ A1 ERROR AMP 400Ω + Z – PULSE WIDTH COMPARATOR SWITCH OUTPUT (VSW) Y LT1176/76-5 • BD 2.2k* VC FB/SENSE 24V (EQUIVALENT) *CONNECTED ON 5V VERSION ONLY U PACKAGE DESCRIPTIO Dimensions in inches (milimeters) unless otherwise noted. N Package 8-Lead Plastic DIP 0.300 – 0.320 (7.620 – 8.128) ( +0.635 8.255 –0.381 ) 0.130 ± 0.005 (3.302 ± 0.127) 0.045 – 0.065 (1.143 – 1.651) 8 7 6 5 0.065 (1.651) TYP 0.009 – 0.015 (0.229 – 0.381) +0.025 0.325 –0.015 0.400 (10.160) MAX 0.250 ± 0.010 (6.350 ± 0.254) 0.125 (3.175) MIN 0.045 ± 0.015 (1.143 ± 0.381) 0.100 ± 0.010 (2.540 ± 0.254) 0.020 (0.508) MIN 1 2 4 3 0.018 ± 0.003 (0.457 ± 0.076) S Package 20-Lead Plastic SOL 0.496 – 0.512 (12.598 – 13.005) 0.291 – 0.299 (7.391 – 7.595) 0.005 (0.127) RAD MIN 0.010 – 0.029 × 45° (0.254 – 0.737) 0.093 – 0.104 (2.362 – 2.642) 0.037 – 0.045 (0.940 – 1.143) 20 19 18 17 16 15 14 13 12 11 0° – 8° TYP 0.009 – 0.013 (0.229 – 0.330) SEE NOTE 0.016 – 0.050 (0.406 – 1.270) 0.050 (1.270) TYP 0.394 – 0.419 (10.007 – 10.643) SEE 0.004 – 0.012 NOTE (0.102 – 0.305) 0.014 – 0.019 (0.356 – 0.482) TYP NOTE: 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. 1 4 Linear Technology Corporation 2 3 4 5 6 7 8 9 10 LT/GP 0393 10K REV 0 1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1993