For iMac Backlight LED driverThe 34845 series represents high efficiency LED drivers for use in backlighting LCD displays from 10” to 17”. Operating from supplies of 5.0 V to 21 V, the 34845 series is capable of driving up to 16 LEDs in series in six separate strings. The LED current tolerance in the six strings is within ±2% maximum and is set using a resistor to GND.PWM dimming is performed by applying a PWM input signal to the PWM pin which modulates the LED channels directly. An Enable Pin (EN) provides for low power standby. Alternatively, a single wire scheme selects power down when PWM is connected to the Wake pin and held low.The integrated boost converter uses dynamic headroom control to automatically set the output voltage. There are three device versions for boost frequency; 34845C is 600 kHz, and the 34845D is 300 kHz. External compensation allows the use of different inductor/ capacitor combinations.The 34845 includes fault protection modes for LED short and open, overtemperature, overcurrent and overvoltage errors. It features an internally fixed OVP value of 60 V (typical) which protects the device in the event of a failure in the externally programmed OVP. The OVP level can be set by using an external resistor divider. This device is powered using SMARTMOS technology.
