AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
high to enable the device , or drive EN low for shutdown.
Soft-Start
Soft-start allows a gradual increase of the internal current-limit level for the step-up
converter during power-up to reduce input surge currents. As the internal current
source charges the internal soft-start capacitor, the peak N-MOS current is limited by
the voltage on the capacitor. In another story, when toggle or a logic-level transition
on EN pin from low to high, soft-start function must work to enable constant current
charging internal capacitor. When soft-start process has finished or appeared falling
edge of PWM signal on EN pin, soft-start capacitor must be discharged to ground
level.
Cycle-by-Cycle Over-Current Protection
The AT1312 series provides cycle-by-cycle over-current protection. Current limit is
accomplished using a separate dedicated comparator. The cycle-by-cycle current limit
abbreviates the on-time of the N-MOS in event that the current of flowing N-MOS is
greater than the current limit value. The current-limit feature protection against a hard
short or over-current fault at the output.
Over-Voltage Protection
If VOUT is above 16V/23V/28V( for AT1312A/B/C) or LEDs are disconnected from
the circuit, the FB pin is similar to pull down to ground with a sense resistor. This will
cause N-MOS to switch with a maximum duty cycle and come out output
over-voltage. This may cause the LX pin voltage to exceed its maximum voltage
rating to damage built-in N-MOS. In the state, the OVP protection circuitry stops the
internal N-MOS. When VOUT falls below 14V/21V/26V, IC will automatically recover
normal operation.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the AT1312 series.
When the junction temperature exceeds Tj=130 ℃, a thermal sensor activates the
thermal protection, which shuts down the IC, allowing the IC to cool. Once the device
cools down by 10 ℃, IC will automatically recover normal operation. For continuous
operation , do not exceed the absolute maximum junction-temperature rating of
Tj=120 ℃.
Power dissipation consideration
The AT1312 series maximum power dissipation depends on the thermal resistance of
the IC package and circuit board, the temperature difference between the die junction
and ambient air, and the rate of any airflow. The power dissipation in the device
depends on the operating conditions of the regulator. In continuous condition, the
step-up converter power dissipated internally across the internal N-MOS can be
approximated by :
7F, No.9,PARK AVENUE. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
2/23/2006 REV:1.1
Fax: 886-3-563-0879
WWW: http://www.aimtron.com.tw
Email: service@aimtron.com.tw
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AIMTRON [ AIMTRON TECHNOLOGY ]
