FAN5606 Datasheet, PDF (5/9 Pages) Fairchild Semiconductor – Serial LED Driver with Current-Regulated, Step-Up DC/DC Converter

PRODUCT SPECIFICATION
FAN5606
Where V_Ref = 1.22V
25
R=10Kohm
20
15
10
5
R=100kohm
0
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5
VExternal (V)
If the analog input A is driven in digital mode by an open
drain output, it is important to choose the appropriate value
of the pull-up resistor. Its resistance should be low enough to
ensure less than 0.7V dropout, hence VA > (VIN–0.7V), as
required for HIGH logic level:
Rpull-up < ^{7---6-0--0-0--}_µ-m---A--V--- = 11kΩ
Pulse-Width-Modulation (PWM) Control
A variable duty cycle (δ) can modulate any DAC input. Care
should be taken not to use a too low frequency, otherwise a
flickering effect may occur. The minimum range is 100Hz to
1KHz. For a maximum range of LED current, both A and B
inputs can be modulated at the same time.
Open Circuit Protection
A built-in over voltage protection circuit prevents the device
from being damaged when it is powered up with no load.
This circuit reduces the boost converter duty cycle, to a min-
imum thus limiting the output voltage to a safe value when
no load condition is detected. However, the FAN5606 can be
damaged when a full load (Six LEDs driven by 20mA) is
suddenly disconnected from V_OUT. To protect the FAN5606
against this unlikely event, an external 24 V Zener diode can
be connected between V_OUT and GND.
Shutdown Mode
The device can be disabled by applying LOW logic level
voltage to the A and B inputs. In Shutdown mode the supply
current is reduced to less than 1µA.
PWM Control
1. A is PWM Controlled, B is Low. I_LED (Average) = δ x 5mA, where δ is Duty Cycle. (Note 4)
A Input (PWM)
ss
B Input (0)
30%
Duty Cycle
1KHz
ss
ss
70%
Duty Cycle
1KHz
I_LED (Average) = 0.7 x 5mA = 3.5mA
I_LED (Average) = 0.3 x 5mA = 1.5mA
ILED
0mA
ss
OFF
2. A is High and B is PWM. I_LED (Average) = 5mA + δ x 15mA, where δ is Duty Cycle.(Note 5, 6)
A Input
ss
B Input (PWM)
ILED
REV. 1.0.3 1/7/05
ss
0mA
30%
Duty Cycle
1KHz
ss
ss
70%
Duty Cycle
1KHz
I_LED (Average) = 0.7 x 20mA + 0.3 x 5mA = 15.5mA
I_LED (Average) = 0.3 x 20mA + 0.7 x 5mA = 9.5mA
ss
OFF
5