MP2489 – STEP DOWN WLED DRIVER WITH WIDE 6V–60V INPUT VOLTAGE

MP2489 Rev. 1.23

www.MonolithicPower.com

7

10/11/2012

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OPERATION

Steady State

The MP2489 is a hysteretic controlled step down

LED driver that is easily to be configured in

varies applications ranging from 6V–60V input.

The converter employs a high side current

sensing resistor to detect and regulate the LED

current. The voltage across the current sensing

resistor is kept measured and regulated in

202mV±30mV range.

The internal 1.275V reference voltage is utilized

to provide a 0.2V reference for enabling the part

and a 1.275V pulling-up voltage as current

reference voltage. When VEN>0.2V, the output

of the comparator becomes high and the other

blocks are enabled.

Output current is sensed by high-side resistor

Rsense. When the switch is on, R2 is shorted

and output current upper-threshold is fixed by R1.

When the switch is off, output current lower-

threshold is fixed by R1 and R2. Ratio of R1 and

R2 determines the current hysteresis.

Enable Control

Once Input voltage is applied, the internal 1.275V

reference is connected to EN/DIM pin through

pull up resistor. If EN/DIM is left open, the IC will

automatically start up to the maxim brightness.

Appling a capacitor on this pin can hereby

program a soft start time.

If an external voltage range from 1.275V to 1.25V

is applied to this pin, the current sensing voltage

reference is linearly controlled from 0mV to

202mV. By controlling the EN/DIM pin voltage

the analog dimming can be easily employed.

If an external PWM voltage is applied on this pin,

the IC will follow the PWM duty to achieve the

PWM dimming, the PWM signal amplitude must

be about 1.25V. About the flexible external PWM

dimming method, please refer to the selecting

dimming control mode section.

System Soft Start

The voltage on the EN/DIM pin is the inductor

current reference. An external capacitor from the

EN/DIM pin to ground provides a soft-start delay.

the capacitor from 0V to 1.25V to fulfill soft-start

function.

Dimming Control

MP2489 provides two dimming methods: PWM

dimming and DC analog dimming.

To use PWM dimming, apply a square wave to

the EN/DIM pin. To use analog dimming, apply a

0.3V–2.5V DC voltage to this pin.

Maximum Continuous Switching Current

MP2489 max continuous switching current

depends on the package with different thermal

resistance. The table 1 shows the max

continuous current corresponding package for

reference.

Table 1. Imax vs. package

Package

TSOT23-5

QFN6

SOIC8E

Imax(A)

1.00

1.41

1.44