LT1777 Linear Technology, LT1777 Datasheet
LT1777
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LT1777 Summary of contents
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... LTC and LT are registered trademarks of Linear Technology Corporation 220 H V OUT 5V + 400mA 100 F 36.5k 10V MBRS1100 1% 12.1k 1% 1777 TA01 LT1777 Switching Regulator U pin, thereby minimizing power drawn CC supply (see Applications Informa Switching Waveforms VOLTAGE 10V/DIV V SW CURRENT 200mA/DIV ...
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... Pin Voltage ...................................................... 30V CC FB Pin Voltage ........................................................ 3.0V Operating Junction Temperature Range LT1777C ............................................... 125 C LT1777I ........................................... – 125 C Storage Temperature Range ................ – 150 C Lead Temperature (Soldering, 10 sec)................. 300 C ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are at T ...
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... Inductor dI/dt rate will cause a somewhat higher current limit in actual application. CONDITIONS I = 0.5A SW (Note 3) Duty Cycle = 0% Switching Action On Switching Action Off SHDN V = 1.25V SHDN Note 4: During normal operation the V below ground. However, the LT1777 may not be used in an inverting DC/DC configuration. LT1777 = MIN TYP MAX UNITS 1.0 1.5 V 0.55 0.70 1 ...
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... LT1777 W U TYPICAL PERFOR A CE CHARACTERISTICS Minimum Input Voltage vs Temperature 7.4 7.2 7.0 6.8 6.6 6.4 6.2 6.0 –50 – TEMPERATURE ( C) Switch Current Limit vs Duty Cycle 1000 800 600 400 200 DUTY CYCLE (%) SHDN Pin Current vs Voltage 5 0 –5 –10 –15 – ...
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... G09 750 25 C 125 C 700 –55 C 650 600 550 500 450 400 1.4 1.5 1777 G11 LT1777 Minimum Synchronization Voltage vs Temperature 50 100 125 –50 – TEMPERATURE ( C) 1777 G08 V Pin Switching Threshold, C Clamp Voltage vs Temperature CLAMP VOLTAGE SWITCHING THRESHOLD 50 100 125 – ...
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... LT1777 PIN FUNCTIONS GND (Pins 16): These corner package pins are mechanically connected to the die paddle and thus aid in conducting away internally generated heat. As these are electrically connected to the die substrate, they must be held at ground potential. A direct connection to the local ground plane is recommended ...
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... SWDR COMP LOGIC SWON FEEDBACK AMP SWITCH ON SIGNAL LT1777 SENSE – dV/dt LIMITER dI/dt 5 LIMITER 1777 BD L SENSE L MAIN V OUT + NOTE 1777 SS 7 ...
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... Output Stage Simplified Schematic. Note that an extra, small-valued inductor, termed the “sense inductor” has been added to the classic buck topology. As this inductor is external to the LT1777, its value can be chosen by the user allowing for optimization on a per application basis. Operation of the current slew limiter is as follows: The ...
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... Nevertheless, more sensitive applications can opt for a closed type magnetic construction on the sense inductor Figure 1. High Speed Current Switching Paths Selecting Sense Inductor The LT1777 uses an external sense inductor to set a theoretical limit for current ramp rate according to the formula: Max dI dt LT1777 LT1777 L SENSE ...
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... This will yield the highest efficiency possible in a given situation. Although an explicit current slew rate no longer exists, the naturally less aggressive nature of the LT1777 will often yield quieter supply operation than other stan- dard switching regulators. ...
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... All photos were taken with the LT1676 and is for comparison purposes. Figures 4b and 4c are of the LT1777 with a sense inductor and 2.2 H, respectively. A decrease in high fre- quency energy is seen when going from the LT1676 to the ...
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... Figures 2 and 24V 5V OUT Voltage Waveform Behavior Unlike current behavior, voltage slew rate of the LT1777 is not adjustable by the user. No component selection or other action is required. Nevertheless instructive to examine typical behavior. The oscilloscope photos in Figure 5 show the V voltage waveform with an input ...
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... V User selection of an appropriate output capacitor is rela- tively easy, as this capacitor sees only the AC ripple current in the inductor L1. As the LT1777 is designed for buck or step-down applications, output voltage will nearly always be compatible with tantalum type capacitors, which are generally available in ratings up to 35V or so ...
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... Their relatively low ESR in the mid-MHz region can further attenuate high speed glitches. Maximum Load/Short-Circuit Considerations The LT1777 is a current mode controller. It uses the V node voltage as an input to a current comparator, which turns off the output switch on a cycle-by-cycle basis as this peak current is reached ...
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... Switch Node Considerations). Switch Node Considerations In spite of the fact that the LT1777 is a low noise converter still possible for the part to cause problems by “coupling to itself.” Specifically, this can occur if the V pin is allowed to capacitively couple in an uncontrolled manner to the part’ ...
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... LT1777 U U APPLICATIONS INFORMATION As an example, assume that the capacitance between the V node and a high impedance pin node is 0.1pF, and that SW the high impedance node in question exhibits a capaci- tance of 1pF to ground. Also assume a “typical” 36V 5V application. Due to the large voltage excursion at ...
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... SGND C3 2200pF 7 L1: SENSE INDUCTOR CAN VARY FROM 2 PER APPLICATION. GRAPHICAL DATA TAKEN WITH D01608C-102, COILCRAFT OR SIMILAR 2 D01608C-222, COILCRAFT OR SIMILAR (SEE TEXT) L2: COILCRAFT D03316-224 OR SIMILAR (SEE TEXT) Figure 8. Basic 5V Output Application LT1777 L2 220 H V OUT 100 F 36 ...
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... I (mA) LOAD 36V OUT 36V (mA) LOAD Figure 9. Efficiency and LT1777 Internal Dissipation for the Basic 5V Output Application 18 1 SENSE 1.0 2.2 H 0.8 0.6 0.4 0.2 100 1000 1777 F09a 1 SENSE 0 H 1.2 1 0.8 2.2 H 0.6 0.4 0.2 100 ...
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... Internal Power Dissipation graphs are shown in Figure 11 for input voltages of 12V, 24V and 36V, and for sense inductor values and 2 interesting to note that internal LT1777 dissipation is very close to the 5V example. This confirms the fact that internal LT1777 V IN ...
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... I (mA) LOAD 36V 3.3V OUT 36V (mA) LOAD Figure 11. Efficiency and LT1777 Internal Dissipation for the Basic 3.3V Output Application 20 1 SENSE 1 1 0.8 2.2 H 0.6 0.4 0.2 100 1000 1777 F11a 1.4 1 SENSE 0 H 1.0 0 0.6 2.2 H 0.4 0.2 100 ...
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... D1 FB SGND 7 V NODE VOLTAGE IN AC COUPLED 50mV/DIV V NODE CURRENT IN DC COUPLED 50mA/DIV GND, CH2 1777 F13a Figure 13. Input Node Ripple LT1777 . Ripple current is also seen P-P , with P-P . P OUT + C8 100 F 10V ADDITIONAL FILTER COMPONENTS L3: COILCRAFT D01608C-333 OR SIMILAR L4: COILCRAFT D01608C-472 OR SIMILAR C8: AVX D CASE TPSD107M010R0080 ...
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... As the input voltage is and ground IN decreased to roughly 18V, switching action will stop, V will drop to zero, and the LT1777 will draw its V quiescent currents from the V voltage, typically 10V the voltage on the SHDN pin will drop to the shutdown threshold, and the part ...
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... DWG # 05-08-1610 0.228 – 0.244 (5.791 – 6.197 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) TYP LT1777 0.386 – 0.394* (9.804 – 10.008 0.150 – 0.157** (3.810 – 3.988 0.004 – ...
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... The only disadvantage is that due to the increased resistance in the inductor, the circuit is no longer capable of withstanding indefinite short circuits to ground. The LT1777 will still current limit at its nominal I LIM Momentary short circuits of a few seconds or less can still be tolerated ...