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LT1176-5 Datasheet(PDF) 3 Page - Linear Technology |
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LT1176-5 Datasheet(HTML) 3 Page - Linear Technology |
3 / 4 page 3 LT1176/LT1176-5 PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Pin Bias Current (LT1176) VFB = VREF q 0.5 2 µA Reference Voltage (LT1176) VC = 2V q 2.155 2.21 2.265 V Reference Voltage Tolerance (LT1176) VREF (Nominal) = 2.21V ±0.5 ±1.5 % All Conditions of Input Voltage, Output q ±1.0 ±2.5 % Voltage, Temperature and Load Current Sense Voltage (LT1176-5) VC = 2V q 4.85 5 5.15 V Sense Voltage Tolerance (LT1176-5) VOUT (Nominal) = 5V ±0.5 ±2% All Conditions of Input Voltage, q ±1.0 ±3% Temperature and Load Current Sense Pin Divider Resistance (LT1176-5) 3 5 8 k Ω Output Voltage Line Regulation 8V ≤ VIN ≤ VMAX (Note 7) q 0.005 0.02 %/ V VC Voltage at 0% Duty Cycle 1.5 V Over Temperature q – 4.0 mV/ °C Multiplier Reference Voltage 24 V Shutdown Pin Current VSHDN = 5Vq 510 20 µA VSHDN ≤ VTHRESHOLD (≅ 2.5V) q 50 µA Shutdown Thresholds Switch Duty Cycle = 0 q 2.2 2.45 2.7 V Fully Shut Down q 0.1 0.30 0.5 V Status Window As a Percent of Output Voltage ±4 ±5 ±6% Status High Level ISTATUS = 10µA Sourcing q 3.5 4.5 5.0 V Status Low Level ISTATUS = 1.6mA Sinking q 0.25 0.4 V Status Delay Time 9 µs Status Minimum Width 30 µs ELECTRICAL C C HARA TERISTICS T J = 25°C, VIN = 25V, unless otherwise noted 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. The q denotes specifications which apply over the full operating tempera- ture 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 start- up 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 transconduc- tance 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)]/2E 5(VIN)(L) Example: VIN = 15V, VOUT = 5V, ILOAD = 0.5A Continuous, 0.8A Peak, L = 100 µH 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. 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 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. |
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