LTC3419
Dual Monolithic 600mA
Synchronous Step-Down
Regulator
DESCRIPTION
FEATURES
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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
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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 (
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