A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
threshold (VUVLO-0.2V). This prevents the switch working with excessive 'on' resistance under conditions
where the duty cycle is high.
Thermal Considerations
When operating the device at high ambient temperatures, or when driving maximum load current, care must
be taken to avoid exceeding the package power dissipation limits. The graph below gives details for power
derating. This assumes the device to be mounted on a 25mm2 PCB with 1oz copper standing in still air.
Note that the device power dissipation will most often be a maximum at minimum supply voltage. It will
also increase if the efficiency of the circuit is low. This may result from the use of unsuitable coils, or
excessive parasitic output capacitance on the switch output.
Thermal Compensation of Output Current
High luminance LEDs often need to be supplied with a temperature compensated current in order to maintain
stable and reliable operation at all drive levels. The LEDs are usually mounted remotely from the device, so
internal circuits for the A8180 have been optimized to minimize the change in output current when no
compensation is employed. If output current compensation is required, it is possible to use an external
temperature sensing network - normally using Negative Temperature Coefficient (NTC) thermistors and/or
diodes, mounted very close to the LED(s). The output of the sensing network can be used to drive the ADJ pin
in order to reduce output current with increasing temperature.
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 16 -
AITSEMI [ AiT Semiconductor ]
