LT3518HFE#TRPBF Linear Technology, LT3518HFE#TRPBF Datasheet - Page 10

• Manufacturer Part Number: LT3518HFE#TRPBF
• Description: IC LED DRIVR AUTOMOTIVE 16-TSSOP
• Manufacturer: Linear Technology
• Type: Automotiver

Specifications of LT3518HFE#TRPBF

• Constant Current: Yes
• Constant Voltage: Yes
• Topology: PWM, Step-Down (Buck), Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: Automotive, Backlight
• Type - Secondary: White LED
• Frequency: 250kHz ~ 2.5MHz
• Voltage - Supply: 3 V ~ 30 V
• Voltage - Output: 7V
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Operating Temperature: -40°C ~ 150°C
• Current - Output / Channel: 2.8A
• Internal Switch(s): Yes
• Efficiency: 88%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
LT3518
For a buck or a buck-boost configuration, the output voltage
is typically level-shifted to a signal with respect to GND as
illustrated in the Figure 4. The output can be expressed as:
Inductor Selection
The inductor used with the LT3518 should have a satura-
tion current rating of 2A or greater. For buck mode LED
drivers, the inductor value should be chosen to give a
ripple current “∆I” of ~30% to 40% of the LED current.
In the buck mode, the inductor value can be estimated
using the formula:
V
voltage to the converter, and t
In the boost configuration, the inductor can be estimated
using the formula:
10
LED
L µH
D
L µH
D
V
OUT
BUCK
BOOST
( )
( )
is the voltage across the LED string, V
=
=
=
=
R2
R1
=
D
D
V
V
BUCK
BOOST
V
LED
LT3518
IN
• 1.01V + V
LED
V
FB
LED
– V
• t
• t
Q1
SW
IN
∆I
SW
R1
R2
3518 F04
(µs) • V
Figure 4
BE(Q1)
(µs) • V
∆I
+
–
V
OUT
SW
(
IN
IN
is the switching period.
– V
R
SENSE
LED
LED
ARRAY
)
IN
is the input
(5)
(6)
(7)
Table 1 provides some recommended inductor vendors.
Table 1. Inductor Manufacturers
VENDOR
Sumida
Toko
Cooper
Vishay
Input Capacitor Selection
For proper operation, it is necessary to place a bypass
capacitor to GND close to the V
1µF or greater capacitor with low ESR should be used. A
ceramic capacitor is usually the best choice.
In the buck mode configuration, the capacitor at the input
to the power converter has large pulsed currents due to
the current returned though the Schottky diode when the
switch is off. For best reliability, this capacitor should have
low ESR and ESL and have an adequate ripple current
rating. The RMS input current is:
where D is the switch duty cycle. A 2.2µF ceramic type
capacitor is usually sufficient.
Output Capacitor Selection
The selection of output capacitor depends on the load
and converter configuration, i.e., step-up or step-down.
For LED applications, the equivalent resistance of the LED
is typically low, and the output filter capacitor should be
sized to attenuate the current ripple.
To achieve the same LED ripple current, the required filter
capacitor value is larger in the boost and buck-boost mode
applications than that in the buck mode applications. For
LED buck mode applications, a 1µF ceramic capacitor
is usually sufficient. For the LED boost and buck-boost
mode applications, a 2.2µF ceramic capacitor is usually
sufficient. Very high performance PWM dimming appli-
cations may require a larger capacitor value to support
the LED voltage during PWM transitions.
I
IN(RMS)
=I
LED
• (1– D) • D
PHONE
[phone]
[phone]
[phone]
[phone]
IN
pin of the LT3518. A
WEB
www.sumida.com
www.toko.com
www.cooperet.com
www.vishay.com
3518fd
(8)