Specifications

AOZ197
8
Page 11 of 11
Rev. 1.0 January 2012
www.aosmd.com
Detailed Description
The AOZ1978 is a dual channel boost DC/DC
controller designed to power a series of LEDs by
regulating the current into an LED string. The LED
current information is provided to the system through
the sense resistor RFB at the bottom of each LED
string, between FB and GND pins.
Protection Features
Over-Current Protection at Boost Switch
The current limit is a function of RCS resistor value at
CS pin and the internal set threshold of 0.4V limit.
When CS voltage reaches set voltage, current limit
protection triggers and the boost switch will turn off
immediately until the next clock cycle. To make sure
that current limit protection does not affect the normal
operation, the current limit should be set at least 30%
higher than the inductor peak current. When CS
voltage is higher than 0.48V, fault detection is
activated and FLAG is asserted.
Over-Voltage Protection at Output
Over-voltage protection is monitoring the LED output
voltage through a resistor divider (Rovh and Rovl in
Typical Application Circuit) from VOUT to OVP and
GND pins. When the voltage at this pin is higher than
1V, the controller will stop switching immediately and
FLAG is asserted for 40ms.
LED Short Protection
When FB voltage exceeds 1V, the system will
consider some or all LEDs shorted instantaneously.
Under this condition, the controller will shut down and
reset every 40ms, this is the only Fault condition that
FLAG will not be asserted.
LED Open Protection
When all LEDs are open, the system will respond by
boosting the output voltage. Once the output voltage
reaches the OVP threshold, OVP protection will
trigger and the controller will latch off until VIN is
recycled.
Feedback short
AOZ1978 also protects against shorted feedback
sense resistor or LED cathode shorted to GND. When
SCP pin voltage drops below 0.96V due to excess
return current sensed by resistor R
RTN
the controller
asserts FLAG and shuts down .It will reset every
40ms until fault condition is removed.
Thermal Protection
An internal temperature sensor monitors the junction
temperature. It shuts down the internal control circuit
and all drivers if the junction temperature exceeds
145ºC.