AT1314
Preliminary Product Information
High-Efficiency Step-Down
Current Regulator For LEDs
General Description
The AT1314 features a PWM step-down converter operating with a fixed switching
frequency of 600 KHz and uses internal power MOSFET to provide maximum
efficiency. The output voltage of the converter can be set as low as 0.4V with external
resistive divider. When trans-conductance signal is higher than saw-tooth wave, then
PWM comparator will produce ON-time signal to set internal flip-flop, which turns
on the switching power MOSFET. The external inductor current ramps up linearly,
storing energy in a magnetic field. Once peak current of flowing through switching
power MOSFET over current-limited threshold or trans-conductance signal level is
lower than saw-tooth wave, the switching power MOSFET will turns off, the flip-flop
resets, and external schottky diode turns on. This forces the current through the
inductor to ramp back down, transferring the energy stored in the magnetic field to the
output capacitor and load. To add higher flexibility to the selection of external
component values, the device uses external loop compensation.
Soft-Start
AT1314 is built-in soft-start function. When power up, after input voltage is above the
under-voltage lockout threshold, then soft-start allows a gradual increase of COMP voltage to
get to a steady state operating point. Therefore, reducing input surge currents. During this
time, the COMP voltage increases and the output duty cycle is allowed to increase from zero
to the value required for regulation. The maximum load current is available after the soft-start
cycle is completed. When EN pin is taken low, the soft-start capacitor is discharge to ground.
Cycle-by-Cycle Over-Current Protection
The AT1314 provides cycle-by-cycle over-current protection. Current limit is
accomplished using a separate dedicated comparator. If the current sense amplifier
output voltage is larger than current-limited threshold level, it will be immediately
turned off power MOS. The current-limit feature protects against a hard short or over
current fault at the output.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the AT1314. When the junction
temperature exceeds Tj=160 ℃, a thermal sensor activates the thermal protection, which shuts
down the IC, allowing the IC to cool. Once the device cools down by 15 ℃, IC will
automatically recover normal operation. For continuous operation , do not exceed the absolute
maximum junction-temperature rating of Tj=150 ℃.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
1/17/2006 REV:1.0
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
Email: service@aimtron.com.tw
7
GMT [ GLOBAL MIXED-MODE TECHNOLOGY INC ]
