lm2746mxax National Semiconductor Corporation, lm2746mxax Datasheet
lm2746mxax
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lm2746mxax Summary of contents
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... IC can be used for providing startup delay, and the soft-start pin can be used for implementing precise tracking, for the purpose of sequencing with respect to an external rail. Typical Application © 2005 National Semiconductor Corporation Features n Power stage input voltage from 1V to 16V ± ...
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... Connection Diagram Ordering Information Order Number LM2746MXA LM2746MXAX Pin Description BOOT (Pin 1) - Bootstrap pin. This is the supply rail for the gate drivers. When the high-side MOSFET turns on, the voltage on this pin should be at least one gate threshold above the regulator input voltage V IN MOSFET ...
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Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications BOOT Voltage All other pins Junction Temperature Storage Temperature Soldering Information Lead Temperature (soldering, 10sec) Electrical Characteristics ...
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Electrical Characteristics V = 3.3V unless otherwise indicated. Limits in standard type are for T CC junction temperature (T ) range of -40˚C to +125˚C. Minimum and Maximum limits are guaranteed through test, design, or sta- J tistical correlation. Typical ...
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Typical Performance Characteristics Efficiency (V = 1.2V) OUT V = 3.3V 300kHz CC SW Efficiency (V = 3.3V) OUT 300kHz CC SW BOOT Pin Current vs Temperature for BOOT Voltage = 3.3V f ...
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Typical Performance Characteristics BOOT Pin Current vs Temperature for BOOT Voltage = 12V f = 300kHz, FDS6898A FET, No-Load SW Frequency vs Temperature Switch Waveforms (HG Rising 3.3V 5V 4A, C ...
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Typical Performance Characteristics Start-Up (No-Load 3.3V 5V OUT C = 12nF 300kHz SS SW Shutdown (Full-Load 3.3V 5V OUT ...
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Typical Performance Characteristics Line Transient Response ( 3.3V OUT 300kHz OUT SW www.national.com (Continued 9V) Line Transient Response ( 1.2V 20147754 3V) ...
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Block Diagram Application Information THEORY OF OPERATION The LM2746 is a voltage-mode, high-speed synchronous buck regulator with a PWM control scheme designed for use in set-top boxes, thin clients, DSL/Cable modems, and other applications that require high efficiency ...
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Application Information Where and kΩ. SW FADJ TRACKING A VOLTAGE LEVEL The LM2746 can track the output of a master power supply during soft-start by connecting a resistor divider to the SS/ TRACK ...
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Application Information FIGURE 4. Sequencing Circuit A desired delay time t between the startup of the DELAY master supply output voltage and the LM2746 output voltage can be set based on the SD pin low-to-high threshold V and the slew ...
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Application Information too (both drivers are ground referenced, i.e. no floating driver). To fully turn the top MOSFET on, the BOOT voltage must be at least one gate threshold greater than V the high-side drive goes high. This bootstrap voltage ...
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Application Information FIGURE 8. LM78L05 Feeding Basic Charge Pump Figure 9 shows a second possibility for bootstrapping the MOSFET drives using a doubler. This circuit provides an equal voltage drive and ...
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Application Information as inductor current has fallen to the current limit threshold. The LM2746 will continue to skip high-side MOSFET pulses until the inductor current peak is below the current limit threshold, at which point the system resumes normal opera- ...
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Application Information FIGURE 11. Maximum Duty Cycle 125˚C J Input Capacitor The input capacitors in a Buck converter are subjected to high stress due to the input current trapezoidal waveform. Input capacitors are selected for their ...
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... Alternatively, the DSON 1.3 can be ignored and the R of the MOSFET estimated DSON using the R Vs. Temperature curves in the MOSFET DSON datasheets. Gate charging loss results from the current driving the gate capacitance of the power MOSFETs, and is approximated as where ‘ ...
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Application Information FIGURE 12. Power Stage and Error Amp One popular method for selecting the compensation compo- nents is to create Bode plots of gain and phase for the power stage and error amplifier. Combined, they make the overall bandwidth ...
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Application Information as high as possible. Two zeroes f and f Z1 double pole frequency to cancel the double pole phase lag. Then, a pole placed at the frequency of the ESR zero final pole f ...
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Application Information In practice, a good trade off between phase margin and bandwidth can be obtained by selecting the closest capacitor values above what are suggested for C ± the closest 10% capacitor value below the suggestion for ± C ...
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Application Information OUT P = 0 300kHz x 31ns 61.38mW SW The FDS6898A has a typical turn-on rise time t fall ...
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Example Circuits PART PART NUMBER U1 LM2746 Q1 FDS6898A D1 MBR0520LTI L1 DO3316P-472 C 1 16SP100M 6SP220M VJ1206Y104KXXA CC BOOT VJ0805Y332KXXA C3 C VJ0805A123KXAA SS C ...
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Example Circuits (Continued) PART PART NUMBER U1 LM2746 Q1 FDS6898A D1 MBR0520LTI L1 DO3316P-682 C 1 16SP100M 10SP56M VJ1206Y104KXXA CC BOOT VJ0805Y182KXXA C3 C VJ0805A123KXAA SS ...
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Example Circuits (Continued) PART PART NUMBER U1 LM2746 Q1 FDS6898A D1 MBR0520LTI L1 DO3316P-332 C 1 16SP100M 6SP220M VJ1206Y104KXXA CC BOOT VJ0805Y222KXXA C3 C VJ0805A123KXAA SS ...
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Physical Dimensions inches (millimeters) unless otherwise noted National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and ...