aoz1950 Alpha & Omega Semiconductor, aoz1950 Datasheet - Page 5

• Manufacturer Part Number: aoz1950
• Description: Boost Regulator White Led Driver
• Manufacturer: Alpha & Omega Semiconductor

Functional Description
AOZ1950 is a constant off time boost converter that is
ideal for white LED backlight applications. The operating
input voltage range is from 2.7V to 5.5V and can support
up to 12 in series LED’s, with the maximum allowed
output voltage set at 53V. The LED current is set by a
series feedback resistor, located at the bottom of the LED
string. The feedback voltage of the controller is set at
300mV for minimum power loss. AOZ1950 features two
dimming control modes, analog and digital dimming. In
analog dimming, fine adjustment of ±12% of the LED
current can be achieved. In PWM digital dimming, a logic
level pulse width is used to set the output LED current.
The duty cycle of the PWM is proportionally to the LED
current. In this dimming mode, the PWM frequency is set
between from 200Hz to 1kHz with duty cycle from 10% to
100%.
Adaptive Constant Pulse Width Control
In a typical constant off time controller, the switching
frequency changes with duty cycle.The duty cycle
relationship of the boost converter entails that if either the
input voltage decreases or the output voltage increases,
the (1-D) off time will decrease. AOZ1950 features an
adaptive constant off-time control that senses the input
and output voltage while maintaining a constant
switching frequency of 800 kHz. In a typical LED
application of 5.5V input and 40V output (12 LEDs), the
off pulse width will be approximately 150ns.
Rev. 1.0 January 2010
300
250
200
150
100
50
0
2.5
Figure 2. Pulse Width vs. Input Voltage
3.0
3.5
Input Voltage (V)
4.0
4.5
V
V
V
IN
IN
IN
= 20V
= 36V
= 50V
5.0
www.aosmd.com
5.5
Over Current Protection
Under normal operation, cycle by cycle over-current
protection will limit the input peak inductor current from
increasing beyond 1.1A nominally.
Output Short Protection
When an output to ground short is detected, a secondary
short circuit protection current level of 1.3A is activated.
During this event the PMOS input protection switch along
with the output boost switch are disabled simultaneously
and the AOZ1950 will shutdown. The system will restart
with a power cycle when either VIN or EN are toggled.
Over Voltage Protection
An over-voltage protection scheme monitors the output
voltage and limits the maximum transient to 53V. The
voltage rating is defined for the maximum voltage stress
of the Mosfet, output boost diode, and output capacitors.
300
250
200
150
100
50
0
20
Figure 3. Pulse Width vs. Output Voltage
25
30
Output Voltage (V)
35
40
V
V
V
OUT
OUT
OUT
= 5.5V
= 3.3V
= 2.7V
AOZ1950
Page 5 of 14
45
50