LT3517
APPLICATIONS INFORMATION
performance, size and cost. The compensation resistor
Board Layout
and capacitor at V are selected to optimize control loop
C
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,
resistanceinserieswiththeseinputsshouldbeminimized
and matched, otherwise there will be an offset. Finally, the
stability. For typical LED applications, a 10nF compensa-
tion capacitor at V is adequate and a series resistor is not
C
required.Acompensationresistormaybeusedtoincrease
the slew rate on the V pin to maintain tighter regulation
C
of LED current during fast transients on V or CTRL.
IN
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
increaseswiththetemperature,fromtheoutputduringthe
PWM low interval. Therefore, choose the Schottky diode
with sufficiently low leakage current. Table 3 has some
recommended component vendors.
bypass capacitor on the V supply to the LT3517 should
IN
be placed as close as possible to the V terminal of the
IN
device.
Table 3. Schottky Diodes
PART NUMBER
Diodes Inc.
DFLS160
V (V)
I
(A)
R
AVE
Soft-Start
For many applications, it is necessary to minimize the
inrush current at start-up. The built-in soft-start circuit
significantly reduces the start-up current spike and
outputvoltageovershoot.Atypicalvalueforthesoft-start
capacitor is 0.1μF.
60
40
60
1
Zetex
ZLLS1000TA
International Rectifier
10MQ060N
1
1.5
3517fa
11
Linear [ Linear ]
