ISL97631 Ver la hoja de datos (PDF) - Renesas Electronics

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Fabricante

ISL97631

White LED Boost Regulator With Integrated Schottky Diode

Renesas Electronics 

ISL97631

Block Diagram

Vin

1.13.52MMHHz Oscillator and Ramp

Generator

Enable

ISL97631

LX

Vout

PWM

Comparator

PWM Logic

Controller

FET

Driver

Current

Sense

-

GM Amp

Compensation

GM

Amplifier 95mV

Bandgap

Reference

Generator

GND

FB

FIGURE 7. ISL97631 BLOCK DIAGRAM

Pin Descriptions

PIN

PIN

NUMBER NAME

DESCRIPTION

1

VOUT Output Pin. Connect to the anode of the top

LED and the output filter capacitor .

2

GND Ground Pin. Connect to local ground.

3

LX Switching Pin. Connect to inductor.

4

ENAB Enable Pin. Connect to enable signal to turn-on

or off the device.

5

FB Feedback Pin. Connect to the cathode of

bottom LED and the sense resistor.

6

VIN Input Supply Pin. Connect to the input supply

voltage, the inductor and the input supply

decoupling capacitor.

Detailed Description

The ISL97631 uses a constant frequency, current mode

control scheme to provide excellent line and load regulation.

It can drive up to 6 LEDs in series or 15 LEDs in

parallel/series configuration, with efficiencies of up 85%. The

ISL97631 operates from an input voltage of 2.7V to 5.5V and

can boost up to 27V.

Steady-State Operation

The ISL97631 operates with constant frequency PWM. The

switching frequency is around 1.35MHz. Depending on the

input voltage, inductance, number of LEDs and the LED

current, the converter operates in either continuous conduction

mode or discontinuous conduction mode. Both are normal. The

forward current of the LED is set using the RSET resistor. In

steady state mode, this current is given by the equation:

ILED = R---V--S--F--E--B--T-

(EQ. 1)

Shut-Down

When taken low the ENAB pin places the ISL97631 into power

down mode. When in power down, the supply current is

reduced to less than 1µA.

Dimming Control

PWM DIMMING

The ENAB pin also doubles as a brightness control. There

are two different possible dimming control methods. The first

dimming method is controlled through the duty-cycle of the

ENAB input PWM waveform, which can operate at

frequencies up to 1kHz. For frequencies greater than 1kHz,

see Analog Dimming. The LEDs operate at either zero or full

current. This is the PWM dimming control method. The

relationship between the average LED current and the duty-

cycle (D) of the ENAB pin’s waveform is as follows:

average ILED = R---V--S--F--E--B--T-  D

(EQ. 2)

FN7370 Rev 1.00

December 21, 2005

Page 4 of 8

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