lt3517 Linear Technology Corporation, lt3517 Datasheet - Page 11

• Manufacturer Part Number: lt3517
• Description: Full-featured Led Driver With 1.5a Switch Current
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
performance, size and cost. The compensation resistor
and capacitor at V
stability. For typical LED applications, a 10nF compensa-
tion capacitor at V
required. A compensation resistor may be used to increase
the slew rate on the V
of LED current during fast transients on V
Diode Selection
The Schottky diode conducts current during the interval
when the switch is turned off. Select a diode rated for
the maximum SW voltage. If using the PWM feature for
dimming, it is important to consider diode leakage, which
increases with the temperature, from the output during the
PWM low interval. Therefore, choose the Schottky diode
with suffi ciently low leakage current. Table 3 has some
recommended component vendors.
Table 3. Schottky Diodes
PART NUMBER
Diodes Inc.
DFLS160
Zetex
ZLLS1000TA
International Rectifi er
10MQ060N
C
C
is adequate and a series resistor is not
are selected to optimize control loop
C
pin to maintain tighter regulation
V
R
60
40
60
(V)
IN
I
or CTRL.
AVE
1.5
1
1
(A)
Board Layout
The high speed operation of the LT3517 demands careful
attention to board layout and component placement. The
Exposed Pad of the package is the only GND terminal of
the IC and is also important for thermal management of
the IC. It is crucial to achieve a good electrical and thermal
contact between the Exposed Pad and the ground plane of
the board. To reduce electromagnetic interference (EMI),
it is important to minimize the area of the SW node. Use
a GND plane under SW and minimize the length of traces
in the high frequency switching path between SW and
GND through the diode and the capacitors. Since there is
a small DC input bias current to the ISN and ISP inputs,
resistance in series with these inputs should be minimized
and matched, otherwise there will be an offset. Finally, the
bypass capacitor on the V
be placed as close as possible to the V
device.
Soft-Start
For many applications, it is necessary to minimize the
inrush current at start-up. The built-in soft-start circuit
signifi cantly reduces the start-up current spike and
output voltage overshoot. A typical value for the soft-start
capacitor is 0.1μF .
IN
supply to the LT3517 should
IN
terminal of the
LT3517
11
3517f