aoz1950 Alpha & Omega Semiconductor, aoz1950 Datasheet - Page 6

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

Thermal Protection
Thermal protection will be activated when the die junction
temperature reaches 145ºC. The system will
automatically restart and lower the junction temperature
to 110ºC.
LED Brightness and Analog Dimming
Applying a voltage between 250mV and 750mV at the
DIM pin will enable analog dimming control for
adjustment of the output LED current. If no adjustment is
required, the DIM pin can be connected to VIN as default.
The percentage of adjustment is set to -12% on the low
end for 250mV and +12% adjustment is obtained when
750mV is applied to the DIM (Figure 4).
LED Brightness and Digital Dimming
Digital dimming provides wider range of LED current
adjustment compared to the analog dimming state.
Forcing a digital PWM signal to the EN pin will activate
the system to enter digital dimming mode. The output
boost switch will be completely shutoff when the PWM is
at logic low state and it will switch on when the PWM is at
logic high. The external PWM frequency ranges between
200Hz and 1kHz. In this mode, the output LED current is
averaged based on the duty cycle of the PWM signal.
Rev. 1.0 January 2010
Figure 4. Analog Dimming I
30
25
20
15
10
5
0
0.25
0.35
Dimming Voltage (V)
0.45
LED
0.55
vs. Dimming Voltage
V
IN
12 LEDs, L = 22µH
= 2.7V, 3.6V 5.5V
0.65
www.aosmd.com
0.75
For example , if the output LED current is set to 30mA at
100% duty ratio, it will be about 3mA with a duty ratio of
10%. AOZ1950 provides an extremely linear relationship
between 10% to 100% (Figure 5). To accommodate both
PWM both dimming and EN functions with the same pin,
a delay disable of 4.5ms is used to differentiate the
events of PWM dimming OFF period and shutdown of the
chip. The figure below (Figure 6) shows the logic
between the two different modes.
Switch Control
Chip Enable
Protection
35
30
25
20
15
10
5
0
EN Pin
PMOS
10
Figure 5. Digital Dimming Characteristics
Figure 6. Logic Sequence Differentiating
20
Dimming Mode and EN Shutdown
30
VIN Level
VIN Level
40
PWM Duty Ratio (%)
GND Level
PMOS On
50
60
tdef > 4.5ms
V
IN
GND Level
= 2.7V, 3.6V 5.5V
12 LEDs, L = 22µH
70
80
AOZ1950
Page 6 of 14
VIN Level
90
GND Level
PMOS Off
100