AT1312A/B/C
Preliminary Product Information
High Efficiency, Constant Current
White-LEDs Driver
Function Description
The AT1312 series are high efficiency and constant current DC-DC converter IC
which is designed primarily for use in LED module applications. The output voltage
of the step-up converter can be set from Vin to 16V/23V/28V with external sense
resistor. The device suits to drive series-connected LEDs and provides even
illumination by sourcing the same output current through each LED. AT1312 series
also consists of a logic shutdown, cycle-by-cycle current-limited, soft-start functions.
Logic control input or PWM duty cycle control allows easy adjustment of LEDs
brightness and on/off control. The average LED current is proportional to the
duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz
and 1KHz.
The boost converter operates in current-mode PWM and a constant frequency of 1.0
MHz. Depending on duty cycle of each switching cycle can regulate output voltage.
On the rising edge of the internal clock, the control and driver logic block sets internal
flip-flop when the output voltage is too low, which turns on the N-MOS. The external
inductor current ramps up linearly, storing energy in a magnetic filed. Once peak
current of inductor over trans-conductance output level, the N-MOS 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 LEDs. To reduce external components, the device will be
built-in internal loop compensation.
Enable Control
Digital logic of EN provides an electrical ON/OFF control of the power supply.
Connecting this pin to ground or to any voltage less than 0.7V and sustain the level
over 4ms will completely turn off the regulator. In this state, current drain from the
input supply is less than 1uA, the internal reference, error amplifier, comparators, and
biasing circuitry turn off. If holding time of low level is less than 3ms on this pin, then
the device only shutdown driver logic block.
Dimming Control
Digital logic of EN also provides LEDs brightness control by applying a PWM signal
on EN pin. With this way, the LEDs operate with either zero or full current. The
average LED current is proportional to the duty-cycle of the PWM signal. Typical
PWM frequency should be between 100Hz and 1KHz. Output current is given by:
200mV ×TON −PWM
RSENSE ×TS−PWM
ILED
=
Where:
TON-PWM : On time of PWM signal
TS-PWM : A cycle time of PWM signal
If dimming control is not required , EN works as a simple on/off control. Drive EN
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 ]
