LTM8040IV#PBF Linear Technology, LTM8040IV#PBF Datasheet - Page 11

• Manufacturer Part Number: LTM8040IV#PBF
• Description: IC, LED DRIVER/CURRENT SOURCE, LGA-66
• Manufacturer: Linear Technology

Specifications of LTM8040IV#PBF

• Led Driver Application: Automotive, Avionic Lighting
• No. Of Outputs: 1
• Output Current: 1A
• Output Voltage: 13V
• Input Voltage: 4V To 36V
• Dimming Control Type: PWM
• Topology: Buck
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATION INFORMATION
Programming LED Current
The LED current can be set by adjusting the voltage on the
ADJ pin. The ADJ pin is internally pulled up to a precision
1.25V voltage source through a 5.11k 1% resistor. This
resistor makes it easy to adjust the LED current with a
single external resistor. For a 1A LED current, leave the
ADJ pin fl oating. For lower output currents, apply a re-
sistor from ADJ to GND as shown in Figure 3, using the
following formula:
where I
In order to have accurate LED current, a precision 1%
resistor is recommended.
The LEDA voltage must be at least 2.5V for proper current
regulation. See Table 2 for recommended R
R
ADJ
LED
= 5.11k • I
is the desired current out of LEDA.
Figure 3. Setting ADJ with a Resistor
LED
R
ADJ
/(1A – I
ADJ
LTM8040
GND
LED
8040 F03
),
ADJ
values.
Dimming Control
There are several different types of dimming control
circuits. Analog dimming control (Figure 4) changes the
voltage on the ADJ pin by tying a low on-resistance FET to
the resistor. This allows the selection of two different LED
currents. For reliable operation, program an LED current of
no less than 35mA. The maximum current dimming ratio
(I
(I
RATIO
MAX
I
I
MAX
MIN
) and the minimum LED current (I
) can be calculated from the maximum LED current
Figure 4. Dimming with an NFET and Resistor
=I
RATIO
DIM
R2
ADJ
LTM8040
GND
8040 F04
LTM8040
MIN
) as follows:
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