PT4115 Ver la hoja de datos (PDF) - Unspecified

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Fabricante

PT4115

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

OPERATION DESCRIPTION

The device, in conjunction with the coil (L1) and

current sense resistor (RS), forms a self oscillating

continuous-mode buck converter.

When input voltage VIN is first applied, the initial

current in L1 and RS is zero and there is no output from

the current sense circuit. Under this condition, the

output of CS comparator is high. This turns on an

internal switch and switches the SW pin low, causing

current to flow from VIN to ground, via RS, L1 and the

LED(s). The current rises at a rate determined by VIN

and L1 to produce a voltage ramp (VCSN) across RS.

When (VIN-VCSN) > 115mV, the output of CS

comparator switches low and the switch turns off. The

current flowing on the RS decreases at another rate.

When (VIN-VCSN) < 85mV, the switch turns on again

and the mean current on the LED is determined by

(

85+ 115

2

mV

)

/

RS

=

100mV

/ RS

.

The high-side current-sensing scheme and on-board

current-setting circuitry minimize the number of

external components while delivering LED current with

±5% accuracy, using a 1% sense resistor.

The PT4115 allow dimming with a PWM signal at the

DIM input. A logic level below 0.3V at DIM forces

PT4115 to turn off the LED and the logic level at DIM

must be at least 2.5V to turn on the full LED current.

The frequency of PWM dimming ranges from 100Hz to

more than 20 kHz.

The DIM pin can be driven by an external DC voltage

(VDIM) to adjust the output current to a value below the

nominal average value defined by RS. The DC voltage

is valid from 0.5V to 2.5V. When the dc voltage is

higher than 2.5V, the output current keeps constant.

The LED current also can be adjusted by a resistor

connected to the DIM pin. An internal pull-up resistor

(typical 200KΩ) is connected to a 5V internal regulator.

The voltage of DIM pin is divided by the internal and

external resistor.

The DIM pin is pulled up to the internal regulator (5V)

by a 200KΩ resistor. It can be floated at normal

working. When a voltage applied to DIM falls below

the threshold (0.3V 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 95uA and switch leakage is

below 5uA.

Additionally, to ensure the reliability, the PT4115 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 PT4115 can handle a

large amount of current safely.

China Resources Powtech (Shanghai) Limited

PT4115_DS Rev EN_2.9

WWW.CRPOWTECH.COM

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