FAN5606 Fairchild Semiconductor, FAN5606 Datasheet - Page 5

• Manufacturer Part Number: FAN5606
• Description: Serial LED Driver with Current-Regulated/ Step-Up DC/DC Converter
• Manufacturer: Fairchild Semiconductor

REV. 1.0.2 5/14/04
PRODUCT SPECIFICATION
Where
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:
PWM Control
1. A is PWM Controlled, B is Low. I
2. A is High and B is PWM. I
25
20
15
10
A Input
B Input (PWM)
I LED
5
0
1.25
V
A Input (PWM)
B Input (0)
I LED
Ref
1.5
=
R=10Kohm
Rpull-up
1.22V
1.75
0mA
2
0mA
<
700mV
----------------- -
2.25
60µA
V
External
LED
Duty Cycle
2.5
Duty Cycle
I
LED
1KHz
30%
(V)
1KHz
30%
R=100kohm
=
I
(Average) = 5mA +
(Average) = 0.3 x 20mA + 0.7 x 5mA = 9.5mA
LED
2.75
11kΩ
(Average) = 0.3 x 5mA = 1.5mA
LED
3
(Average) =
3.25
3.5
δ
δ
x 15mA, where
x 5mA, where
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
against this unlikely event, an external 24 V Zener diode can
be connected between V
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 1 µ A.
δ
δ
is Duty Cycle. (Note 4 )
is Duty Cycle.(Note 5, 6)
I
LED
Duty Cycle
I
Duty Cycle
LED
1KHz
70%
1KHz
70%
(Average) = 0.7 x 20mA + 0.3 x 5mA = 15.5mA
(Average) = 0.7 x 5mA = 3.5mA
OUT
and GND.
OUT
. To protect the FAN5606
OFF
OFF
FAN5606
5