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MAX1642-MAX1643 Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX1642-MAX1643 Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 12 page High-Efficiency, Step-Up DC-DC Converters for 1V Inputs 8 _______________________________________________________________________________________ BATTLO (MAX1643) The MAX1643 contains an on-chip comparator for low- battery detection. If the voltage at BATT drops below 1V, BATTLO sinks current. BATTLO is an open-drain output. In combination with PFI/PFO, this allows moni- toring of both the input and output voltages. Reverse-Battery Protection The MAX1642/MAX1643 can sustain/survive single-cell battery reversal up to the package power-dissipation limit. An internal 5 Ω resistor in series with a diode limits reverse current to less than 220mA, which prevents dam- age to the MAX1642/MAX1643. Prolonged operation above 220mA reverse-battery current can degrade the devices’ performance. ________________Design Information Output Voltage Selection The MAX1642/MAX1643 operate with a 3.3V ±4% or adjustable output. To select fixed-voltage operation, con- nect FB to GND. For an adjustable output between 2V and 5.2V, connect FB to a resistor voltage divider between OUT and GND (Figure 4). FB regulates to 1.23V. Since FB leakage is 10nA max, select feedback resistor R2 in the 100k Ω to 1MΩ range. R1 is given by: where VREF = 1.23V. Power-Fail Detection The MAX1642/MAX1643 have an on-chip comparator for power-fail detection. This comparator can detect loss of power at the input or output. If the voltage at PFI falls below 614mV, the PFO output sinks current to GND. Hysteresis at the power-fail input is 1%. The power-fail monitor’s threshold is set by two resistors: R3 and R4 (Figure 5). Set the threshold using the following equation: where VTH is the desired threshold of the power-fail detector, and VPFI is the 614mV reference of the power- fail comparator. Since PFI leakage is 10nA max, select feedback resistor R4 in the 100k Ω to 1MΩ range. Low-Battery Start-Up The MAX1642/MAX1643 are bootstrapped circuits with a low-voltage start-up oscillator. They can start under low-load conditions at lower battery voltages than at full load. Once started, the output can maintain the load as the battery voltage decreases below the start-up volt- age (see Typical Operating Characteristics). Inductor Selection A 100µH inductor is recommended for most appli- cations. The use of lower inductor values (down to 68µH) increases maximum output current. Higher val- ues (up to 220µH) reduce peak inductor current and consequent ripple and noise. The inductor’s saturation- current rating must exceed the peak current limit syn- thesized by the MAX1642/MAX1643’s timing algorithms: where KMAX = 35V-µs. The maximum recommended IPEAK is 350mA. For best efficiency, inductor series resistance should be less than 1 Ω. I = K L PEAK MAX MIN R3 = R4 V V - 1 TH PFI R1 = R2 V V - 1 OUT REF MAX1642 GND FB BATT PFI 3.3VOUT 0.88V to 1.65V INPUT 100 µH, 350mA PF0 22 µF 0.1 µF SHDN LX OUT OUT 22 µF 0.1 µF MAX1643 GND FB BATT 3.3VOUT 0.88V to 1.65V INPUT BATTLO 22 µF 0.1 µF LX OUT PFI PFO 22 µF 0.1 µF OUT 100 µH, 350mA Figure 2. MAX1642 3.3V Standard Application Circuit Figure 3. MAX1643 3.3V Standard Application Circuit |
Similar Part No. - MAX1642-MAX1643 |
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Similar Description - MAX1642-MAX1643 |
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