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BL9582 Rev 1.2

Belling Proprietary Information. Unauthorized Photocopy and Duplication Prohibited

2/2010

©2010 Belling All Rights Reserved

14

BL9582

32V, 1.4A Step-down

High Brightness LED Driver with Internal Switch

dimming, by reducing the rate of rise of

LED voltage. By adding this capacitor the

current waveform through the LED(s)

changes from a triangular ramp to a more

sinusoidal version without altering the

mean current value.

Operation at low supply voltage

The internal regulator disables the drive to

the switch until the supply has risen above

threshold, the device will start to operate.

However, with the supply voltage below the

specified minimum value, the switch duty

cycle will be high and the device power

dissipation will be at a maximum. Care

should be taken to avoid operating the

device under such conditions in the

application, in order to minimize the risk of

exceeding the maximum allowed die

temperature. (See next section on thermal

considerations). The drive to the switch is

turned off when the supply voltage falls

0.2V). This prevents the switch working

with excessive 'on' resistance under

conditions where the duty cycle is high.

Thermal considerations

When operating the device at high ambient

temperatures, or when driving maximum

load current, care must be taken to avoid

exceeding the package power dissipation

limits. The graph below gives details for

power derating. This assumes the device

copper standing in still air.

Note that the device power dissipation will

most often be a maximum at minimum

supply voltage. It will also increase if the

efficiency of the circuit is low. This may

result from the use of unsuitable coils, or

excessive parasitic output capacitance on

the switch output.

-40

-20

0

20

40

60

80

100

120

140

0

200

400

600

800

1000

1200

1400

1600

Ambient Temperature

Max. Power Dissipation

Thermal compensation of output

current

High luminance LEDs often need to be

supplied with a temperature compensated

current in order to maintain stable and

reliable operation at all drive levels. The

LEDs are usually mounted remotely from

the device, so internal circuits for the

BL9582 have been optimized to minimize

the change in output current when no

compensation is employed. If output

current compensation is required, it is

possible to use an external temperature

sensing network - normally using Negative

Temperature Coefficient (NTC) thermistors

and/or diodes, mounted very close to the

LED(s). The output of the sensing network

can be used to drive the ADJ pin in order

to reduce output current with increasing

temperature.

Thermal shutdown protection

To ensure the reliability, the BL9582 is built

with a thermal shutdown (TSD) protection

function. The TSD protests the IC from

over temperature (160 ). When

℃

the chip