LTC3419IMS-1#PBF

LTC3419 Dual Monolithic 600mA Synchronous Step-Down Regulator DESCRIPTION FEATURES n n n n n n n n n n n n n n n n High Efficiency Dual Step-Down Outputs: Up to 96% 600mA Current per Channel at VIN = 3V Only 35μA Quiescent Current During Operation (Both Channels) 2.25MHz Constant-Frequency Operation 2.5V to 5.5V Input Voltage Range Low Dropout Operation: 100% Duty Cycle No Schottky Diodes Required Internally Compensated for All Ceramic Capacitors Independent Internal Soft-Start for Each Channel Available in Fixed Output Versions Current Mode Operation for Excellent Line and Load Transient Response 0.6V Reference Allows Low Output Voltages User-Selectable Burst Mode® Operation Short-Circuit Protected Ultralow Shutdown Current: IQ < 1μA Available in Small MSOP or 3mm × 3mm DFN-8 Packages APPLICATIONS n n n n n Cellular Telephones Digital Still Cameras Wireless and DSL Modems Portable Media Players PDAs/Palmtop PCs The LTC®3419 is a dual, 2.25MHz, constant-frequency, synchronous step-down DC/DC converter in a tiny 3mm × 3mm DFN package. 100% duty cycle provides low dropout operation, extending battery life in portable systems. Low output voltages are supported with the 0.6V feedback reference voltage. Each regulator can supply 600mA output current. The input voltage range is 2.5V to 5.5V, making it ideal for Li-Ion and USB powered applications. Supply current during operation is only 35μA and drops to 1μF) input capacitors. The discharged input capacitors are effectively put in parallel with COUT , causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the switch connecting the load has low resistance and is driven quickly. The solution is to limit the turn-on speed of the load switch driver. A Hot Swap™ controller is designed specifically for this purpose and usually incorporates current limiting, short-circuit protection, and soft-starting. Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: % Efficiency = 100% – (L1 + L2 + L3 + ...) where L1, L2, etc., are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four sources usually account for the losses in LTC3419 circuits: 1) VIN quiescent current, 2) switching losses, 3) I2R losses, 4) other system losses. 1. The VIN current is the DC supply current given in the Electrical Characteristics which excludes MOSFET driver and control currents. VIN current results in a small (