LT3518EFE#PBF Linear Technology, LT3518EFE#PBF Datasheet - Page 9

• Manufacturer Part Number: LT3518EFE#PBF
• Description: IC LED DRIVR AUTOMOTIVE 16-TSSOP
• Manufacturer: Linear Technology
• Type: Automotiver

Specifications of LT3518EFE#PBF

• 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 ~ 125°C
• Current - Output / Channel: 2.8A
• Internal Switch(s): Yes
• Efficiency: 88%
• Led Driver Application: Display Backlighting, Automotive And Avionic Lighting
• No. Of Outputs: 1
• Output Current: 2.3A
• Output Voltage: 45V
• Input Voltage: 3V To 30V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
Dimming Control
There are two methods to control the current source for
dimming using the LT3518. The first method uses the
PWM pin to modulate the current source between zero
and full current to achieve a precisely programmed aver-
age current. To make this method of current control more
accurate, the switch demand current is stored on the V
node during the quiescent phase. This feature minimizes
recovery time when the PWM signal goes high. To further
improve the recovery time, a disconnect switch is used in
the LED current path to prevent the output capacitor from
discharging in the PWM signal low phase. The minimum
PWM on or off time will depend on the choice of operating
frequency through R
ing the SYNC function, the SYNC and PWM signals must
have the aligned rising edges to achieve the optimized
high PWM dimming ratio. For best current accuracy, the
minimum PWM low or high time should be at least six
switching cycles (3µs for f
period is determined by the system and is unlikely to be
longer than 12ms. The maximum PWM dimming ratio
(PWM
period (t
as follows:
Example:
The second method of dimming control 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, the LED current is:
t
PWM
PWM
I
MAX
LED
RATIO
=
= 9ms, t
RATIO
MAX
RATIO
10 • R
) can be calculated from the maximum PWM
) and the minimum PWM pulse width (t
V
CTRL
= 9ms/3µs = 3000:1
=
SENSE
MIN
t
t
MAX
MIN
= 3µs (f
T
input pin or SYNC pin. When us-
SW
SW
= 2MHz). Maximum PWM
= 2MHz)
MIN
(1)
(2)
C
)
When V
to be:
The LED current programming feature possibly increases
total dimming range by a factor of ten.
The CTRL pin should not be left open (tie to V
used). The CTRL pin can also be used in conjunction with
a PTC thermistor to provide overtemperature protection
for the LED load.
Setting Output Voltage
For a boost application, the output voltage can be set by
selecting the values of R1 and R2 (see Figure 3) according
to the following equation:
V
I
LED
OUT
CTRL
=
=
R
100mV

 
SENSE
R2
R1
is higher than 1V, the LED current is clamped
V
+ 1
REF

 
• 1.01V
LT3518
45.3k
5k
PTC
Figure 2
Figure 3
FB
2V
V
OUT
R1
R2
3518 F03
3518 F02
49.9k
CTRL
LT3518
REF
if not
3518fd
9
(3)
(4)