HV9903 Ver la hoja de datos (PDF) - Supertex Inc

Número de pieza

componentes Descripción

Fabricante

HV9903

White LED Driver

Supertex Inc 

HHVV99990033

Diode Selection

Since the HV9903 operates at a 1.2MHz switching

frequency, the output rectifier must be fast – 20ns or

less. The faster the diode, the more efficiently the

driver operates. Also, choose a diode with low

capacitance to improve performance. A Schottkey

need not be used, although its lower forward voltage

drop improves efficiency. Peak current rating is the

same as for the inductor. Average current is simply

the LED current. To be compatible with the HV9903’s

open LED protection, the diode’s reverse voltage

rating should be 35V or more. Otherwise, the diode’s

voltage rating should be greater than the LED string’s

voltage drop plus 1 volt.

Dimming

Dimming may be accomplished in one of two ways:

DC dimming or PWM dimming. DC dimming linearly

regulates the current through the LEDs in a

continuous fashion, while PWM dimming rapidly turns

the LEDs on and off while maintaining a constant ‘on’

current. In PWM dimming, the ratio of on to off time

determines perceived brightness. The on/off

frequency must be high enough to prevent visible

flickering – typically above 70Hz. The claimed

advantage of PWM dimming is less color shift as the

LED is dimmed, although the effect is virtually

imperceptible.

DC dimming is accomplished by applying a bias to the

RSET resistor.

DC Dimming

L

D

COUT

HV9903

1 SW

VDD 6

2 GND SHDN 5

3 LED

RSET 4

VDD

CDD

Shutdown

RBIAS

RSET

VDIM

ILED

225 100mV

RSET

VDIM 100mV

RBIAS

DC Dimming Frequency Response

+10

0

-10

-20

-30

-40

-50

100

1k

10k

100k

Frequency (Hz)

PWM dimming may be implemented via the SHDN

input or via RSET. Since SHDN reactivates soft-start, a

delay is introduced (~1ms) to LED turn-on. For this

reason, it is better to use the RSET pin for PWM

dimming, as it does not include the soft-start delay.

PWM dimming frequency should be in the range of

70-100Hz to minimize the effect of turn-on delays

while avoiding flicker.

PWM Dimming via SHDN

L

D

COUT

HV9903

1 SW

VDD 6

2 GND SHDN 5

3 LED RSET 4

ILE D ( avg)

D 22.5V

RSET

VDD

CDD

PWM

RSET

7

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