LTM8040 datasheet(6/16 Pages) LINER

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LTM8040

8040p

BLOCK DIAGRAM

VIN

SHDN

PWM

GND

ADJ

80.6k

5.11k

INTERNAL

1.25V

0.1μF

4.7μF

8.2μH

SENSE

RESISTOR

LPWR

LEDA

BIAS

INTERNAL

COMPENSATION

CURRENT

MODE

CONTROLLER

8040 BD

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(Bank3):TheVINpinsuppliescur-renttotheLTM8040’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.

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