PPMIC BU

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BL9582 Rev 1.2

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2/2010

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12

BL9582

32V, 1.4A Step-down

High Brightness LED Driver with Internal Switch

therefore the LED color does not vary with

brightness as it does with analog dimming.

Pulsing the current provides precise

brightness control while preserving the

color purity. The dimming frequency of

BL9582 can be as high as 20 kHz.

Shutdown mode

Taking the ADJ pin to a voltage below 0.2V

will turn off the output and the supply

current will fall to a low standby level of

50μA nominal.

Soft-start

An external capacitor from the ADJ pin to

ground will provide soft-start delay, by

increasing the time taken for the voltage on

this pin to rise to the turn-on threshold.

Adding capacitance increases this delay by

approximately 0.06ms/nF.

Inherent open-circuit LED protection

If the connection to the LED(s) is open-

circuited, the coil is isolated from the LX

pin of the chip, so the device will not be

damaged.

Capacitor selection

A low ESR capacitor should be used for

input decoupling, as the ESR of this

capacitor appears in series with the supply

source impedance and lowers overall

efficiency. This capacitor has to supply the

relatively high peak current to the coil and

smooth the current ripple on the input

supply. A minimum value of 4.7uF is

acceptable if the input source is close to

the device, but higher values will improve

performance at lower input voltages,

especially when the source impedance is

high. The input capacitor should be placed

as close as possible to the IC.

For maximum stability over temperature

and voltage, capacitors with X7R, X5R, or

better dielectric are recommended. Cap-

acitors with Y5V dielectric are not suitable

for decoupling in this application and

should not be used. A suitable Murata

capacitor would be GRM42-2X7R475K-50.

The following web sites are useful when

finding alternatives:

www.murata.com

www.t-yuden.com

www.avxcorp.com

Inductor selection

Recommended inductor values for the

BL9582 are in the range 27uH to 100uH.

Higher values of inductance are re-

commended at lower output current in

order to minimize errors due to switching

delays, which result in increased ripple and

lower efficiency. Higher values of in-

ductance also result in a smaller change in

output current over the supply voltage

range. The inductor should be mounted as

close to the device as possible with low

pins. The chosen coil should have a

saturation current higher than the peak

output current and a continuous current

rating above the required mean output

current. Suitable coils for use with the

BL9582 are listed in the table below:

Part No.

L

(uH)

DCR

(

Ω)

(A)

Manufacturer

MSS1038-

333

33

0.093

2.3

MSS1038-

473

47

0.128

2

MSS1038-

683

68

0.213

1.6

MSS1038-

104

100

0.304

1.3

CoilCraft

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