LM2797/LM2798 120mA High Efficiency Step-Down Switched Capacitor Voltage Converter with Voltage Monitoring
April 2003
...
LM2797/LM2798 120mA High Efficiency Step-Down Switched Capacitor
Voltage Converter with
Voltage Monitoring
April 2003
LM2797/LM2798 120mA High Efficiency Step-Down Switched Capacitor
Voltage Converter with
Voltage Monitoring
General Description
The LM2797/98 switched capacitor step-down DC/DC converters efficiently produce a 120mA regulated low-
voltage rail from a 2.6V to 5.5V input. Fixed output
voltage options of 1.5V, 1.8V, and 2.0V are available. The LM2797/98 uses multiple fractional gain configurations to maximize conversion efficiency over the entire input
voltage and output current ranges. Also contributing to high overall efficiency is the extremely low supply current of the LM2797/98: 35µA operating unloaded and 0.1µA in shutdown. Features of the LM2797/98 include input
voltage and output
voltage monitoring. Pin BATOK provides battery monitoring by indicating when the input
voltage is above 2.85V (typ.). Pin POK verifies that the output
voltage is not more than 5% (typ.) below the nominal output
voltage of the part. The optimal external component requirements of the LM2797/98 solution minimize size and cost, making the part ideal for Li-Ion and other battery powered designs. Two 1µF flying
capacitors and two 10µF bypass
capacitors are all that is required, and no inductors are needed. The LM2797/98 also features short-circuit protection overtemperature protection, and soft-start circuitry to prevent excessive inrush currents. The LM2798 has a 400µs turn-on time. T...
