PT4115B89E Ver la hoja de datos (PDF) - Unspecified

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PT4115B89E

30V, 1.2A Step-down High Brightness LED Driver with 5000:1 Dimming

Unspecified 

PT4115

30V, 1.2A Step-down High Brightness

LED Driver with 5000:1 Dimming

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. When

the application is limited by the internal power

dissipation of the device, the ESOP8 package is

recommended because of its enhanced power

dissipation ability.

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，for this reason, the temperature coefficients of the

internal circuits for the PT4115 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

DIM pin in order to reduce output current with

increasing temperature.

Thermal shutdown protection

To ensure the reliability, the PT4115 is built with a

thermal shutdown (TSD) protection function. The TSD

protests the IC from over temperature (160℃). When

the chip temperature decreases (140℃), the IC recovers

again.

Layout considerations

Careful PCB layout is critical to achieve low switching

losses and stable operation. Use a multilayer board

whenever possible for better noise immunity. Minimize

ground noise by connecting high-current ground returns,

the input bypass-capacitor ground lead, and the

output-filter ground lead to a single point (star ground

configuration).

SW pin

The SW pin of the device is a fast switching node, so

PCB tracks should be kept as short as possible. To

minimize ground 'bounce', the ground pin of the device

should be soldered directly to the ground plane.

Coil and decoupling capacitors and current sense

resistor

It is particularly important to mount the coil and the

input decoupling capacitor as close to the device pins as

possible to minimize parasitic resistance and inductance,

which will degrade efficiency. It is also important to

minimize any track resistance in series with current

sense resistor RS. It’s best to connect VIN directly to

one end of RS and CSN directly to the opposite end of

RS with no other currents flowing in these tracks. It is

important that the cathode current of the Schottky diode

does not flow in a track between RS and VIN as this

may give an apparent higher measure of current than is

actual because of track resistance.

China Resources Powtech (Shanghai) Limited

PT4115_DS Rev EN_2.9

WWW.CRPOWTECH.COM

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