A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
DETAILED INFORMATION
The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a self oscillating
continuous-mode buck converter. When input voltage VIN is first applied, the initial current in L1 and RS is zero
and there is no output from the current sense circuit. Under this condition, the (-) input to the comparator is at
ground and its output is high. This turns on an internal switch and switches the LX pin low, causing current to
flow from VIN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by VIN and L1 to
produce a voltage ramp (VISENSE) across RS. When (VIN-VISENSE) > 115mV, the output of comparator switches
low and the switch turns off. The current flowing on the RS decreases at another rate. When (VIN- VISENSE
)
< 85mV, the switch turns on again and the mean current on the LED is determined by
85 +115
(
)mV / RS = 100mV / RS
2
The high-side current-sensing scheme and on-board current-setting circuitry minimize the number of external
components while delivering LED current with ±4% accuracy, using a 1% sense resistor.
The A8180 allows dimming with a PWM signal at the ADJ input. A logic level below 0.2V at ADJ forces A8180
to turn off the LED and the logic level at ADJ must be at least 1.2V (1.5V recommended) to turn on the full
LED current. The frequency of PWM dimming ranges from 100Hz to more than 20 kHz.
The ADJ pin can be driven by an external DC voltage (VADJ) to adjust the output current to a value below the
nominal average value defined by RS. The DC voltage is valid from 0.3V to 1.2V. When the dc voltage is
higher than 1.2V, the output current keeps constant. The LED current also can be adjusted by a resistor
connected to the ADJ pin. An internal pull- up resistor (typical 1.0 MΩ) is connected to a 5V internal regulator.
The voltage of ADJ pin is divided by the internal and external resistor. The ADJ pin is pulled up to the internal
regulator (5V) by a 1.0 MΩ resistor. It can be floated at normal working. When a voltage applied to ADJ falls
below the threshold (0.2V nom.), the output switch is turned off. The internal regulator and voltage reference
remain powered during shutdown to provide the reference for the shutdown circuit. Quiescent supply current
during shutdown is nominally 50uA and switch leakage is below 5uA. Additionally, to ensure the reliability, the
A8180 is built with a thermal shutdown (TSD) protection and a thermal pad. The TSD protests the IC from
over temperature (160℃). Also the thermal pad enhances power dissipation. As a result, the A8180 can
handle a large amount of current safely.
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 10 -
AITSEMI [ AiT Semiconductor ]
