LT1777I LINER [Linear Technology], LT1777I Datasheet
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LT1777I
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LT1777I Summary of contents
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FEATURES Programmable dI/dt Limit Internally Limited dV/dt High Input Voltage: 48V Max 700mA Peak Switch Rating True Current Mode Control 100kHz Fixed Operating Frequency Synchronizable to 250kHz Low Supply Current in Shutdown Low Thermal Resistance 16-Pin SO Package ...
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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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ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are 24V, V Open 5V 1.4V unless otherwise noted SYMBOL PARAMETER Output Switch ...
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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 ...
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W U TYPICAL PERFOR A CE CHARACTERISTICS Switching Frequency vs Temperature 106 104 102 100 –50 – TEMPERATURE ( C) Output dI/dt Sense Voltage vs Temperature 2.0 1.8 1.6 1.4 1.2 1.0 0.8 ...
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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 ...
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W BLOCK DIAGRA SHDN 3 BIAS SYNC 12 OSC SGND OUTPUT STAGE SI PLIFIED SCHE ATIC ...
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LT1777 U OPERATIO The LT1777 is a current mode step-down switcher regu- lator IC designed for low noise operation. The Block Diagram shows an overall view of the system. The indi- vidual blocks are straightforward and similar to those found ...
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U U APPLICATIONS INFORMATION Basics of Low Noise Operation Switching power supply circuits are often preferred over linear topologies for their improved efficiency (P However, their typically rapid voltage and current slew rates often cause “radio frequency” interference prob- lems, ...
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LT1777 U U APPLICATIONS INFORMATION Deciding upon a value for the sense inductor involves evaluating the trade-off between overall efficiency ( and switch current slew rate. Larger sense inductors IN yield lower current slew rates which offer reduced ...
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U U APPLICATIONS INFORMATION current waveform. The four sense inductor values 0. and 2.2 H yield dI/dt rates of roughly 4.5A/ s, 2.2A/ s, 1.4A/ s and 0.6A/ s, respectively. These photos show that ...
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LT1777 U U APPLICATIONS INFORMATION 0MHz to 20MHz (2MHz/DIV) (a) LT1676 for Comparison 0MHz to 20MHz (2MHz/DIV) (b) LT1777 with L SENSE 0MHz to 20MHz (2MHz/DIV) (c) LT1777 with L SENSE Figure 4. Spectral Analysis of Current Waveforms in Figures ...
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U U APPLICATIONS INFORMATION GND 500ns/DIV Figure 6. LT1676 V Node Voltage Behavior SW for Comparison Purposes Only, V Selecting Main Inductor There are several parameters to consider when selecting a main inductor. These include inductance value, peak current rating ...
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LT1777 U U APPLICATIONS INFORMATION tors. 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 ...
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U U APPLICATIONS INFORMATION However, remember that oscillator slowdown to achieve short-circuit protection (discussed above) is dependent on FB pin behavior, and this in turn, is sensitive to FB node external impedance. The graph in Figure 7 shows the typical ...
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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 ...
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U TYPICAL APPLICATIONS Basic 5V Output Application Figure 8 shows a basic application that produces 500mA I . Efficiency and Internal Power Dissipation OUT graphs are shown in Figure 9 for input voltages of 12V, 24V ...
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LT1777 U TYPICAL APPLICATIONS Efficiency 12V OUT 12V (mA) LOAD 24V IN ...
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U TYPICAL APPLICATIONS Basic 3.3V Output Application Figure 10 shows a circuit similar to the previous example, but modified for a 3.3V output. Once again, Efficiency and Internal Power Dissipation graphs are shown in Figure 11 for input voltages of ...
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LT1777 U TYPICAL APPLICATIONS Efficiency 12V 3.3V OUT 12V (mA) LOAD 24V IN ...
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U TYPICAL APPLICATIONS Optional Input/Output Filtering When minimum conducted noise is required often advantageous to add an explicit input and/or output filter to the topology. This can be a cost-effective way to reduce conducted noise on the input ...
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LT1777 U TYPICAL APPLICATIONS V NODE OUT AC COUPLED 2mV/DIV 2 s/DIV (a) Before Output Filter User Programmable Undervoltage Lockout Figure 15 uses a resistor divider between V to drive the SHDN node. This is a simple, cost-effective way to ...
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PACKAGE DESCRIPTION 0.010 – 0.020 45 (0.254 – 0.508) 0.008 – 0.010 0 – 8 TYP (0.203 – 0.254) 0.016 – 0.050 (0.406 – 1.270) * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER ...
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LT1777 U TYPICAL APPLICATION Minimum PC Board Size Application The previously described basic applications employ power path parts which are capable of delivering the full rated input supply voltage and output current capabilities of the LT1777. A substantial improvement in ...