ltm8040 Linear Technology Corporation, ltm8040 Datasheet - Page 6

• Manufacturer Part Number: ltm8040
• Description: 36v, 1a ?module Led Driver
• Manufacturer: Linear Technology Corporation

LTM8040
PIN FUNCTIONS
pin fl oating. Please refer to the Applications Information
section for details.
PWM (Pin L7): Input Pin for PWM Dimming Control. A
PWM signal above 0.9V (ON threshold) turns the on output
current source, while a PWM signal below 0.5V shuts it
down. If the application does not require PWM dimming,
then the PWM pin can be left either open (an internal 10μA
source current pulls PWM high) or pulled up to a voltage
source between 1.2V and 10V.
V
internal power converter and other circuitry. It must be lo-
cally bypassed with a high quality (low ESR) capacitor.
ADJ (Pin L3): Use the ADJ pin to scale the LEDA output
current below 1A by either applying a voltage source or by
connecting a resistor to GND. This pin is internally pulled
up to a 1.25V reference through a 5.11K resistor, so ensure
that the voltage source can drive a 5.11K impedance. If
applying a voltage to ADJ, the LEDA current follows the
BLOCK DIAGRAM
6
IN
(Bank 3): The V
SHDN
PWM
V
IN
IN
0.1μF
pin supplies cur-rent to the LTM8040’s
COMPENSATION
INTERNAL
GND
CONTROLLER
CURRENT
MODE
80.6k
RT
ADJ
formula: I
GND, the resistor value should be R = 5.11 • I
– I
out of LEDA in Amps. Make sure that the voltage at LEDA
is at least 2.4V.
RT (Pin L2): The RT pin is used to set the internal oscillator
frequency. An 80.6k resistor has already been installed
inside the LTM8040 to default switching frequency to
500kHz. If no modifi cation of the switching frequency is
necessary, leave this pin fl oating. Otherwise, a parallel
resistor applied from RT to GND will raise the switching
frequency. See table 2 for details.
GND (Bank 2): Tie all GND pins directly to a local ground
plane. These pins serve as both signal and power return
to the LTM8040 μModule, as well as providing the primary
thermal path for heat dissipation within the unit. See the
Applications Information section for more information
about heat-sinking and printed circuit board layout.
LED
5.11k
), where R is in KΩ and I
INTERNAL
LED
1.25V
= 1A • ADJ/1.25V. If connecting a resistor to
8.2μH
4.7μF
LED
RESISTOR
is the desired current
SENSE
8040 BD
LED
LEDA
LPWR
BIAS
/(1Amp
8040p