MP2480 – 36V INPUT, 3A HIGH POWER LED DRIVER

MP2480 Rev. 1.01

www.MonolithicPower.com

9

1/25/2013

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OPERATION

Hysteresis Current Control with Adaptive

Threshold Adjustment

MP2480 operates in a hysteretic current-control

mode to accurately regulate the LED current.

pin to sense the LED current. The power

MOSFET turns on and remains on until the

voltage on the FB pin rises to the upper

threshold of 225mV. The power MOSFET then

turns off and remains off until FB pin falls to the

lower threshold of 175mV. The two thresholds

are adaptive and adjust to compensate for

circuit delay. This regulates the LED current

very accurately with an average of 200mV at

the FB pin.

Enable Control

The MP2480 has a dedicated enable-control

pin (EN) with positive logic. Its falling threshold

is 1.23V, and its rising threshold is 1.55V

(320mV higher).

When floating, EN pulls up to about 3.0V by an

internal 1µA current source so it is enabled.

Pulling down a floating EN requires a current

capability of 1µA..

Floating Driver and Bootstrap Charging

The floating power MOSFET driver is powered

by an external bootstrap capacitor. This floating

driver has its own UVLO protection, with a

rising threshold of 2.2V and a falling threshold

of 150mV.

The dedicated internal bootstrap regulator

charges and regulates the bootstrap capacitor

to around 5V.

In case the internal circuit does not have

sufficient voltage and the bootstrap capacitor

has insufficient charge, extra external circuitry

can ensure that the bootstrap voltage is in the

normal operational region. Refer to External

Bootstrap Diode in the Application section.

Under-Voltage Lockout (UVLO)

Under-voltage lockout (UVLO) protects the chip

from operating at insufficient supply voltage.

The UVLO rising threshold is about 4.0V while

its falling threshold is a consistent 3.6V.

Thermal Shutdown

Thermal shutdown prevents the chip from

operating at exceedingly high temperatures.

When the silicon die temperature rises above

its upper threshold, the chip shuts down. When

the temperature falls below its lower threshold,

the chip is enabled again.

LED Short Protection

The LED current is within its limits and well-

regulates while FB pin voltage is 200mV, as

If the LED sensing resistor has failed or the

output has shorted to GND, the voltage of FB

inductor current reaches the current limit value,

the power MOSFET turns off. MP2480 will retry

the operation after about 300µs delay.