aoz1960 Alpha & Omega Semiconductor, aoz1960 Datasheet - Page 13

• Manufacturer Part Number: aoz1960
• Description: Multi-string Boost White Led Driver
• Manufacturer: Alpha & Omega Semiconductor

voltage, reducing voltage across the LED string. There
are six internal current regulators. Each consists of a
driver, a MOSFET, and a current sense resistor. The
driver controls the MOSFET gate voltage based on the
current sense feedback to achieve current regulation.
When current sense signal is below a preset regulation
point, the driver will reduce the MOSFET drain-to-source
voltage by increasing gate voltage, allowing more voltage
across the LED string. When current sense signal is
above the regulation point, the driver will increase the
MOSFET drain-to-source voltage by lowering gate
voltage, reducing voltage across the LED string.
When one or two LEDs in a string are shorted, the
current regulator in that string takes the additional
voltage drop and continues to regulate LED current. If
four or more LEDs in a string are shorted, the current
regulator in that string is disabled and AOZ1960 ignores
the current feedback signal from that string.
Analog Dimming
AOZ1960 supports analog dimming through ABRT pin. In
analog dimming mode, LED current linearly changes with
ABRT voltage. The current adjustment range is from 10%
to 100% of the full brightness LED current, corresponding
to 0.2V to 2V on ABRT. When ABRT is below 0.2V, LED
current remains at 10%. When ABRT is above 2V, LED
current remains at 100%. To disable analog dimming,
connect ABRT to a voltage higher than 4V.
DPWM Dimming
AOZ1960 supports digital PWM dimming through DBRT
pin. In DPWM dimming mode, current regulators are
turned on and off by a PWM signal on DBRT. The
brightness is proportional to the duty cycle of the PWM
signal. For example, the duty cycle can be adjusted from
3% to 100% for 20kHz DPWM frequency.
Rev. 1.0 August 2010
www.aosmd.com
Applications Information
LED Current Setting
The maximum LED current is set with an external resistor
in ISET pin. The current can be set from 15mA to 25mA.
RSET can be calculated using Eq.1:
To set the LED current from 15mA to 25mA, use the
figure below.
Input Capacitor
The input capacitor is connected to VIN and GND pins of
the AOZ1960 to filter and maintain a steady input DC
voltage. The voltage rating of input capacitor must be
greater than maximum input voltage plus ripple voltage.
The RMS current rating should be greater than the
inductor ripple current:
The input capacitor value should be 22μF or higher for
normal operation. The capacitor can be electrolytic,
tantalum or ceramic. The input capacitor should be place
as close as possible to the IC; if not possible, a 0.1μF
decoupling ceramic capacitor between VIN pin and GND
in close proximity.
I
LED
30
25
20
15
10
5
0
=
36
------------- -
R
928
R
SET
SET
46.4k
62k
37k
AOZ1960DI R
41
(Ω)
(Eq. 1)
46
R
ISET
ISET
(kΩ)
vs. LED Current
51
I
LED
15
20
25
56
(mA)
AOZ1960
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