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BL9582 Rev 1.2

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2/2010

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10

BL9582

32V, 1.4A Step-down

High Brightness LED Driver with Internal Switch

Operation Description

The device, in conjunction with the coil (L1)

self

oscillating

continuous-mode

buck

zero and there is no output from the

current sense circuit. Under this condition,

the (-) input to the comparator is at ground

and its output is high. This turns on an

internal switch and switches the LX pin low,

output of comparator switches low and the

switch turns off. The current flowing on the

and the mean current on the LED is

determined by

85 115

(

)

/

100

/

2

SS

mV R

mV R

+

=

The high-side current-sensing scheme and

on-board current-setting circuitry minimize

the number of external components while

delivering LED current with ±4% accuracy,

using a 1% sense resistor.

The BL9582 allows dimming with a PWM

signal at the ADJ input. A logic level below

0.2V at ADJ forces BL9582 to turn off the

LED and the logic level at ADJ must be at

least 1.2V (1.5V recommended) to turn on

the full LED current. The frequency of

PWM dimming ranges from 100Hz to more

than 20 kHz.

The ADJ pin can be driven by an external

current to a value below the nominal

voltage is valid from 0.3V to 1.2V. When

the dc voltage is higher than 1.2V, the

output current keeps constant. The LED

current also can be adjusted by a resistor

connected to the ADJ pin. An internal pull-

up resistor (typical 1.0 MΩ) is connected to

a 5V internal regulator. The voltage of ADJ

pin is divided by the internal and external

resistor. The ADJ pin is pulled up to the

internal regulator (5V) by a 1.0 MΩ resistor.

It can be floated at normal working. When

a voltage applied to ADJ falls below the

threshold (0.2V nom.), the output switch is

turned off. The internal regulator and

voltage reference remain powered during

shutdown to provide the reference for the

shutdown circuit. Quiescent supply current

during shutdown is nominally 50uA and

switch leakage is below 5uA. Additionally,

to ensure the reliability, the BL9582 is built

with a thermal shutdown (TSD) protection

and a thermal pad. The TSD protests the

IC from over temperature (160 ). Also the

℃

thermal pad enhances power dissipation.

As a result, the BL9582 can handle a large

amount of current safely.

Application Information

Setting nominal average output current

The nominal average output current in the

LED(s) is determined by the value of the

external

current

sense

resistor

given by:

0.1

OUT

S

I

R

=

This equation is valid when ADJ pin is float