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LT3757 Datasheet(PDF) 32 Page - Analog Devices |
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LT3757 Datasheet(HTML) 32 Page - Analog Devices |
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32 / 38 page  LTC7840 32 Rev 0 For more information www.analog.com APPLICATIONS INFORMATION Design Example A two-stage step up converter is shown in Figure 20. The two channels of LTC7840 are connected in cascade, i.e., the output of Channel 1 is tied to the input of Channel 2. The output voltage of Channel 1 is 48V and the output voltage of Channel 2 is 240V. The input voltage range of Channel 1 is 9V to 36V. The maximum output current of Channel 2 is 0.7A when the input voltage of Channel 1 is 12V. 1. The duty cycle range is: DMAX1 = VO1+ VF – VIN1 VO1+ VF ⎛ ⎝⎜ ⎞ ⎠⎟ = 48V + 0.5V – 12V 48V + 0.5V ⎛ ⎝⎜ ⎞ ⎠⎟ = 75.3% DMIN1 = 48V + 0.5V – 36V 48V + 0.5V ⎛ ⎝⎜ ⎞ ⎠⎟ = 25.8% DMAX2 = VO2 + VF – VO1 VO2 + VF ⎛ ⎝⎜ ⎞ ⎠⎟ = 240V + 0.5V – 48V 240V + 0.5V ⎛ ⎝⎜ ⎞ ⎠⎟ = 80% 2. The operating frequency is chosen to be 150kHz so the period is 6.67μs. From Figure 6, the resistor from the FREQ pin to SGND is 73.2k. 3. Channel 2 maximum DC input current is: IIN2(MAX) = IO2(MAX) 1– DMAX2 = 0.7A 1– 0.8 = 3.5A Channel 1 maximum DC input current is: IIN1(MAX) = IO1(MAX) 1– DMAX1 = IIN2(MAX) 1– DMAX1 = 3.5A 1– 0.753 = 14.17A 4. A ripple current of 40% is chosen so the peak current in each inductor is: IL1(PK) = 1+ χ 2 ⎛ ⎝⎜ ⎞ ⎠⎟ •IIN1(MAX) = 1+ 0.4 2 ⎛ ⎝⎜ ⎞ ⎠⎟ • 14.17A = 17A IL2(PK) = 1+ χ 2 ⎛ ⎝⎜ ⎞ ⎠⎟ •IIN2(MAX) = 1+ 0.4 2 ⎛ ⎝⎜ ⎞ ⎠⎟ • 3.5A = 4.2A Figure 20. 12V Input, 240V/0.7A Output Two-Stage Boost Converter SW1 RUN1 ITH1 INTVCC SGND DRVCC PGND LTC7840 7840 F20 1nF 0.1µF 10µF 0805 VFB2 RUN2 PGOOD1 PGOOD2 33nF 100pF 73.2k 12.1k 84.5k 4.7µFx4 100V 1210 + 33µF 63V 10µH SER2918H-103KL V8P10 IDD04SG60C 11.8k 12.1k 475k 0805 15k ITH2 47nF 100pF 46.4k 2.37M 1206 SS2 2.2µF + 2m 2010 1m 2010 10nF 33µFx2 80V 4.7µFx7 100V 1210 + 8m 2010 100µF x2 400V 33µF 80V VOUT1 48V VOUT 240V 0.7A 2.2µFx4 450V 2220 100µH PCV-2-104-05L VIN 12V BLANK CLKOUT SYNC DMAX BSC047N08 STB45N40DM2AG 10 10nF 10 + SW2 GATE2 SENSE2+ SENSE2– VIN GATE1 SENSE1+ ILIM1 SENSE1– GATE2 SENSE2+ ILIM2 SENSE2– VFB1 FREQ SS1 |
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