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ISL97631 Fiches technique(PDF) 4 Page - Intersil Corporation

No de pièce ISL97631
Description  White LED Boost Regulator With Integrated Schottky Diode
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Fabricant  INTERSIL [Intersil Corporation]
Site Internet  http://www.intersil.com/cda/home
Logo INTERSIL - Intersil Corporation

ISL97631 Fiches technique(HTML) 4 Page - Intersil Corporation

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4
FN7370.1
December 21, 2005
Block Diagram
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:
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:
FIGURE 7. ISL97631 BLOCK DIAGRAM
FET
Driver
PWM Logic
Controller
Current
Sense
GM
Amplifier
1.2MHz Oscillator and Ramp
Generator
Bandgap
Reference
Generator
95mV
GM Amp
Compensation
PWM
Comparator
Vin
Enable
LX
GND
FB
ISL97631
Vout
-
FET
Driver
PWM Logic
Controller
Current
Sense
GM
Amplifier
1.2MHz Oscillator and Ramp
Generator
Bandgap
Reference
Generator
95mV
GM Amp
Compensation
PWM
Comparator
Vin
Enable
LX
GND
FB
ISL97631
Vout
-
1.35MHz
Pin Descriptions
PIN
NUMBER
PIN
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.
ILED
VFB
RSET
---------------
=
(EQ. 1)
average ILED
VFB
RSET
--------------- D
=
(EQ. 2)
ISL97631


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