link to page 8 link to page 8 link to page 9 MAX1795/MAX1796/ Low-Supply Current, Step-Up DC-DC Converters MAX1797 with True Shutdown Pin DescriptionPINNAMEFUNCTION 1 LBI Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in shutdown. 2 FB Dual-Mode™ Feedback Input. Connect to GND for preset 5.0V output. Connect to OUT for preset 3.3V output. Connect a resistive voltage-divider from OUT to GND to adjust the output voltage from 2V to 5.5V. 3 LBO Low-Battery Comparator Output, Open-Drain Output. LBO is high impedance when VLBI < 0.85V. This function remains operational in shutdown. 4 SHDN Shutdown Input. If SHDN is high, the device is in shutdown mode, OUT is high impedance, and LBI/LBO are still operational. Connect shutdown to GND for normal operation. 5 GND Ground 6 LX Inductor Connection 7 OUT Power Output. OUT provides bootstrap power to the IC. 8 BATT Battery Input and Damping Switch Connection Detailed Description V The MAX1795/MAX1796/MAX1797 compact step-up IN DC-DC converters start up with voltages as low as 0.85V and operate with an input voltage down to +0.7V. 22µH 47µF 1M Consuming only 25μA of quiescent current, these devices BATT have an internal synchronous rectifier that reduces SHDN LX cost by eliminating the need for an external diode and VOUT = 3.3V improves overall efficiency by minimizing losses in the LBO OUT V MAX1795 C IN OUT* circuit (see Synchronous Rectification section for details). MAX1796 The internal N-channel MOSFET power switch resistance MAX1797 GND is typically 0.17Ω, which minimizes losses. The LX switch current limits of the MAX1795/MAX1796/MAX1797 are LBI FB 0.25A, 0.5A, and 1A, respectively. All three devices offer Maxim’s proprietary True Shutdown *SEE TABLE 1 FOR COMPONENT VALUES. circuitry, which disconnects the output from the input in shutdown and puts the output in a high impedance Figure 1. Typical Application Circuit state. These devices also feature Maxim’s proprietary LX-damping circuitry, which reduces EMI in noise-sensi- pulse-skipping controller (Figure 2). Switching frequency tive applications. For additional in-system flexibility, the depends upon the load current and input voltage, and can LBI/LBO comparator remains active in shutdown. Figure range up to 500kHz. Unlike conventional pulse-skipping 1 is a typical application circuit. DC-DC converters (where ripple amplitude varies with Control Scheme input voltage), ripple in these devices does not exceed the product of the switch current limit and the filter-capacitor A unique minimum-off-time, current-limited control equivalent series resistance (ESR). scheme is the key to the MAX1795/MAX1796/MAX1797s’ low operating current and high efficiency over a wide load range. The architecture combines the high output power and efficiency of a pulse-width-modulation (PWM) device with the ultra-low quiescent current of a traditional Dual Mode is a trademark of Maxim Integrated Products. www.maximintegrated.com Maxim Integrated │ 8
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