Datasheet LTM8040 (Analog Devices) - 6

LTM8040
PIN FUNCTIONS LEDA (Bank 1):
This pin is the regulated current source
VIN (Bank 3):
The VIN pin supplies current to the LTM8040’s of the LTM8040. Connect the anode of the LED string to internal power converter and other circuitry. It must be lo- this pin. This voltage must be at least 2.5V for accurate cally bypassed with a high quality (low ESR) capacitor. current regulation.
ADJ (Pin L3):
Use the ADJ pin to scale the LEDA output
SHDN (Pin L4):
The SHDN pin is used to shut down the current below 1A by either applying a voltage source or by switching regulator and the internal bias circuits. The connecting a resistor to GND. This pin is internally pulled 2.65V switching threshold can function as an accurate up to a 1.25V reference through a 5.11k resistor, so ensure undervoltage lockout. Pull below 0.3V to shut down the that the voltage source can drive a 5.11k impedance. If LTM8040. Pull above 2.65V to enable the LTM8040. Tie applying a voltage to ADJ, the LEDA current follows the to VIN if the SHDN function is unused. formula: ILED = 1A • ADJ/1.25V. If connecting a resistor to
BIAS (Pin L5):
The BIAS pin connects through an internal GND, the resistor value should be R = 5.11 • ILED /(1Amp Schottky diode to provide power to internal housekeeping – ILED), where R is in kΩ and ILED is the desired current circuits. Connect to a voltage source (usually LPWR or V out of LEDA in amps. Make sure that the voltage at LEDA IN) greater than 2.6V. Note that this pin is adjacent to the LPWR is at least 2.5V. pin to ease layout. If this pin is powered by an external
RT (Pin L2):
The RT pin is used to set the internal oscillator power source, a decoupling cap may be necessary. frequency. An 80.6k resistor has already been installed
LPWR (Pin K5):
This is the output of the buck regulator inside the LTM8040 to default switching frequency to that sources the LED current. If the LEDA voltage is above 500kHz. If no modifi cation of the switching frequency is 2.6V, connect this pin to BIAS. It is pinned out primarily necessary, leave this pin fl oating. Otherwise, a parallel for the convenience of the user. If it is not used, leave this resistor applied from RT to GND will raise the switching pin fl oating. Please refer to the Applications Information frequency. See Table 1 for details. section for details.
GND (Bank 2, Pin L1):
Tie all GND pins directly to a local
PWM (Pin L7):
Input Pin for PWM Dimming Control. A ground plane. These pins serve as both signal and power PWM signal above 1.2V (ON threshold) turns on the output return to the LTM8040 μModule, as well as providing current source, while a PWM signal below 0.4V shuts it the primary thermal path for heat dissipation within the down. If the application does not require PWM dimming, unit. See the Applications Information section for more then the PWM pin can be left either open (an internal 10μA information about heat sinking and printed circuit board source current pulls PWM high) or pulled up to a voltage layout. source between 1.2V and 10V. 8040fa 6