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MAX668EUB Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX668EUB Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 18 page Non-Bootstrapped Operation With non-bootstrapped operation, the IC is powered from the input voltage (VIN) or another source, such as a logic supply. Non-bootstrapped operation (Figure 4) is recommended (but not required) for input voltages above 5V, since the EXT amplitude (limited to 5V by LDO) at this voltage range is no higher than it would be with bootstrapped operation. Note that non-boot- strapped operation is required if the output voltage exceeds 28V, since this level is too high to safely con- nect to VCC. Also note that only the MAX668 can be used with non-bootstrapped operation. If the input voltage does not exceed 5.5V, the on-chip regulator can be disabled by connecting VCC to LDO (Figure 5). This eliminates the regulator forward drop and supplies the maximum gate drive to the external FET for lowest on-resistance. Disabling the regulator also reduces the non-bootstrapped minimum input volt- age from 3V to 2.7V. 1.8V to 28V Input, PWM Step-Up Controllers in µMAX ______________________________________________________________________________________ 11 MAX668 LDO CS+ REF FREQ VCC SYNC/ SHDN PGND FB GND N1 EXT VIN = 2.7V to 5.5V C3 0.22 µF C2 1 µF R4 100k 1% R1 0.02 Ω R2 218k 1% R3 24.9k 1% C7 220pF D1 MBRS340T3 C4 68 µF 20V C5 68 µF 20V C6 0.1 µF 3 5 7 6 8 2 4 9 1 10 VOUT = 12V @ 1A C1 68 µF 10V L1 4.7 µH FDS6680 Figure 5. MAX668 Low-Voltage Non-Bootstrapped Configuration MAX668 LDO CS+ REF FREQ VCC PGND FB GND N1 EXT VIN = 3V to 12V C3 0.22 µF C4 1 µF C2 0.1 µF R4 100k 1% R1 0.02 Ω R2 218k 1% R3 24.9k 1% C7 220pF D1 MBRS340T3 C5 68 µF 20V C6 68 µF 20V C8 0.1 µF 3 5 7 6 8 2 4 9 1 10 VOUT = 12V @ 1A C1 68 µF 20V L1 4.7 µH FDS6680 SYNC/ SHDN Figure 4. MAX668 High-Voltage Non-Bootstrapped Configuration |
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