LTM8040 Ver la hoja de datos (PDF) - Linear Technology
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LTM8040 Datasheet PDF : 16 Pages
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LTM8040
PIN FUNCTIONS
pin floating. 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.
VIN (Bank 3): The VIN pin supplies cur-rent to the LTM8040’s
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
formula: ILED = 1A • ADJ/1.25V. If connecting a resistor to
GND, the resistor value should be R = 5.11 • ILED /(1Amp
– ILED), where R is in KΩ and ILED is the desired current
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 modification of the switching frequency is
necessary, leave this pin floating. 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.
BLOCK DIAGRAM
VIN
0.1μF
SHDN
PWM
INTERNAL
COMPENSATION
CURRENT
MODE
CONTROLLER
80.6k
8.2μH
SENSE
RESISTOR
4.7μF
LEDA
LPWR
BIAS
5.11k
INTERNAL
1.25V
GND
RT ADJ
8040 BD
8040p
6
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