MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters_____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) LOAD-TRANSIENT RESPONSESTART-UP DELAY 3V OUTPUT VSHDN VOLTAGE 2V/div 50mV/div 0V 5V OUTPUT VOUT CURRENT 2V/div 0mA to 200mA 0V VIN = 2.5V VIN = 2.5V HORIZONTAL = 50μs/div HORIZONTAL = 5ms/div 5V Mode 5V Mode ______________________________________________________________Pin DescriptionPINNAMEFUNCTIONMAX756MAX757 Shutdown Input disables SMPS when low, but the voltage reference and low-battery com- 1 1 SHDN parator remain active. 2 – 3/5 Selects the main output voltage setting; 5V when low, 3.3V when high. Feedback Input for adjustable output operation. Connect to an external voltage divider – 2 FB between OUT and GND. 1.25V Reference Voltage Output. Bypass with 0.22µF to GND (0.1µF if there is no external 3 3 REF reference load). Maximum load capability is 250µA source, 20µA sink. Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at 4 4 LBO LBI drops below +1.25V. Low-Battery Input. When the voltage on LBI drops below +1.25V, LBO sinks current. 5 5 LBI Connect to VIN if not used. Connect OUT to the regulator output. It provides bootstrapped power to both devices, 6 6 OUT and also senses the output voltage for the MAX756. 7 7 GND Power Ground. Must be low impedance; solder directly to ground plane. 8 8 LX 1A, 0.5Ω N-Channel Power MOSFET Drain 4 Maxim Integrated
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