LT3519 LINER [Linear Technology], LT3519 Datasheet - Page 9

• Manufacturer Part Number: LT3519
• Description: LED Driver with Integrated Schottky Diode
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
determined by the system. The maximum PWM dimming
ratio (PWM
PWM period (t
(t
Example:
The second method of dimming control, Analog Dim-
ming, uses the CTRL pin to linearly adjust the current
sense threshold during the PWM high state. When the
CTRL pin voltage is less than 1V but more than 100mV,
the LED current is:
When V
to be:
MIN
t
I
I
PWM
PWM
MAX
LED
LED
) as follows:
Figure 1. FB Resistor Divider for Boost LED Driver
=
CTRL
=
= 9ms, t
RATIO
RATIO
R
250
V
CTRL
SENSE
RATIO
4
is higher than 1.2V, the LED current is clamped
mV
•
=
=
MAX
R
MIN
–
9
t
) can be calculated from the maximum
3
SENSE
t
MAX
MIN
ms
100
µs
) and the minimum PWM pulse width
= 3μs
LT3519
=
mV
3000 1 :
FB
V
OUT
R1
R2
3519 F01
When V
LED current is in the nonlinear region of V
Threshold vs V
Characteristics.
The LED current programming feature through the CTRL
pin possibly increases the total dimming range by a factor
of ten. In order to have the accurate LED current, precision
resistors are preferred (1% is recommended). The CTRL
pin should not be left open. Tie to V
Programming Output Voltage (Constant Voltage
Regulation) or Open LED/Overvoltage Threshold
For a boost application, the output voltage can be set by
selecting the values of R1 and R2 (see Figure 1) according
to the following equation:
For open LED protection of a boost type LED driver, set
the resistor from the output to the FB pin such that the
expected V
1.1V. For a buck mode or buck-boost mode LED driver,
the output voltage is typically level-shifted to a signal with
respect to GND as illustrated in Figure 2. The open LED
voltage level can be expressed as:
V
V
OUT
OUT
Figure 2. Open LED Protection FB Resistor Connector
for Buck Mode or Buck-Boost Mode LED Driver
CTRL
=
=
V
FB
R2
R1
BE Q
LT3519
is more than 1V but less than 1.2V, the
( )
during normal operation will not exceed
CTRL
+1 • 1.22V
1
+
FB
as shown in the Typical Performance
R
R
2
1
Q1
• .
1 22
R1
R2
3519 F02
+
–
V
OUT
V
100k
REF
R
if not used.
SENSE(EXT)
LT3519
LED
ARRAY
ISP
-V
9
3519f
ISN