LM2647EVAL National Semiconductor, LM2647EVAL Datasheet
LM2647EVAL
Specifications of LM2647EVAL
Related parts for LM2647EVAL
LM2647EVAL Summary of contents
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... Standard supervisory and control features include Soft-start, Power Good, output Under-voltage and Over-voltage protec- tion, Under-voltage Lockout, Soft-shutdown and Enable. Typical Application (Channel 2 in parenthesis) © 2005 National Semiconductor Corporation Features n Input voltage range from 5.5V to 28V n Synchronous dual-channel Interleaved switching ...
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Connection Diagrams Top View 28-Lead TSSOP (MTC) Ordering Information Order Number LM2647MTC LM2647MTCX LM2647LQ LM2647LQX Pin Description (All pin numbers referred to here correspond to the TSSOP package) Pin 1, SENSE1: Output voltage sense pin for Channel ...
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Pin Description (Continued) output capacitors. The voltage on this pin finally clamps close to 5V. This pin is again connected to the internal 115µA current sink whenever a current limit event is in progress. This sink current discharges the Soft-start ...
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Pin Description (Continued) permitted. If not, the upper FET will be turned OFF and will stay so for several cycles if necessary, until the current returns to normal. Eventually, if the overcurrent condition persists, and the upper FET has not ...
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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. Voltages from the indicated pins to SGND/PGND unless otherwise indicated (Note 2): VIN V5 VDD BOOT1, BOOT2 BOOT1 to SW1, BOOT2 to SW2 SW1, SW2 ILIM1, ILIM2 ...
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Electrical Characteristics Specifications with standard typeface are for T ture range. VDD = V5 = 5V, V SGND Symbol Parameter Power Good V Power Good Upper Threshold PGOOD_HI as a Percentage of Internal Reference V Power Good Lower Threshold PGOOD_LOW ...
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Electrical Characteristics Specifications with standard typeface are for T ture range. VDD = SGND Symbol Parameter V Zero-cross Threshold (SW SW_ZERO Pin) Osillator PWM Frequency PWM Ramp Peak-to-peak Amplitude PWM Ramp Valley Frequency Change ...
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Block Diagram www.national.com 8 20056301 ...
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Typical Performance Characteristics uppermost curve to lowermost curve in each of the Efficiency plots below. Efficiency for 5V/3.3V Outputs Efficiency for 1.8V/1.2V Outputs Input Voltage is 15V, 20V, 24V,28V (in order) starting from Efficiency for 2.5V/3.3V Outputs 20056305 Modulator (Plant) ...
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Operation Descriptions GENERAL The LM2647 provides two identical synchronously switched buck regulator channels that operate 180˚ out of phase. A voltage-mode control topology was selected to provide fixed- frequency PWM regulation at very low duty cycles, in pref- erence to ...
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Operation Descriptions In a conventional converter, as the load is decreased to about 10-30% of maximum load current, DCM (Discontinu- ous Conduction Mode) occurs. In this condition the inductor current falls to zero during the OFF-time, and stays there until ...
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Operation Descriptions FIGURE 4. Inductor Current in FPWM Mode Note: A common question is: can one change from FPWM to SKIP Mode ‘on the fly’? That means that the voltage on the FPWM pin would be changed while the converter ...
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Operation Descriptions goes to zero (and stays there). Though not displayed, Power Good also goes low within less than 100ns of the EN pin going low (∆t , see Electrical Characteristics table). There- SD fore in this case, the controller ...
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Operation Descriptions CH1: PGOOD, CH2: VIN, CH3: LDRV, CH4: Vo Output 1V @ 0.02A, VIN = 9.75V, SKIP 10µ 300kHz, C 660µF FIGURE 8. VIN Removal in SKIP Mode The recovery procedure from a VIN Power-off ...
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Operation Descriptions CH1: PGOOD, CH2: Vo, CH3: ILIM Pin, CH4 Output 1V, 0.04A to Overload, VIN = 10V, FPWM 10µ 300kHz, RLIM = 1k FIGURE 9. Response to Severe Overload (Type A: fault threshold ...
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Application Information CURRENT LIMIT RESISTOR The timing scheme implemented in the LM2647 makes it possible for the IC to continue monitoring an overcurrent condition and to respond appropriately every cycle. This is explained as follows. Consider the LM2647 working under ...
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Application Information selected if the output voltage ripple needs to be decreased but it is not desirable to achieve this by adding more (expensive?) output specialty caps. The peak current under normal operation is Conclusions: In this example the peak ...
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Application Information The case of a single input capacitor supplying two channels running out of phase is now discussed in detail and it shows how to formally calculate the input RMS current capability required. The example represents a very general ...
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Application Information the upper FET sees the V-I crossover losses (at turn-ON and at turn-OFF maximize efficiency, high switching speed is certainly needed in this position. This FET position has typically very low conduction losses, especially in a ...
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Application Information FIGURE 13. Crossover (turn-on or turn-off) The V-I crossover losses (exist only in upper FET) are: Pswon_u = 1/2 • VIN • Io • f • ton_u Pswon_u = 464mW Pswoff_u = 1/2 • VIN • Io • ...
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Application Information Note that the current limit detector circuit compares the voltage on the ILIM pin with respect to the PGND pin. Therefore, if the power ground is noisy it can lead to errone- ous triggering of the current limit ...
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Application Information TABLE 2. Summary of Compensation Design Procedure (Continued) πRC, ’s’ stands for series combination. Resonant frequency ⁄ factor to shift entire Gain up or down to acheive good crossover frequency ...
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Bill of Materials Designator Function C1 Cin (Ch #2)* C4 Comp cap (across RC, Ch #2) C5 Comp cap (series with R, Ch #2) C6 Comp cap (series with R, Ch #1) C7 Comp cap (across RC, Ch #1) C14 ...
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PCB Layout Diagrams FIGURE 17. Top Overlay FIGURE 18. Top Layer 25 20056362 20056363 www.national.com ...
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PCB Layout Diagrams www.national.com (Continued) FIGURE 19. Internal Plane 1 (GND) FIGURE 20. Internal Plane 2 26 20056364 20056365 ...
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PCB Layout Diagrams (Continued) FIGURE 21. Bottom Layer 27 20056366 www.national.com ...
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Physical Dimensions www.national.com inches (millimeters) unless otherwise noted 28-Lead TSSOP Package NS Package Number MTC28 28-Lead LLP Package NS Package Number LQA28A 28 ...
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