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OB3328NQP View Datasheet(PDF) - On-Bright Electronics

Part Name
Description
Manufacturer
OB3328NQP
On-Bright
On-Bright Electronics  On-Bright
OB3328NQP Datasheet PDF : 14 Pages
1 2 3 4 5 6 7 8 9 10 Next Last
OB3328/OB3328N
High Performance CCFL Controller Full Bridge
following equation:
frequency is equal to LPWM frequency.
Fstriking (KHz)
=
RI
//
1751
RT (Kohm)
Lamp Current Regulation
e The lamp cu rrent is regul ated by a la mp curren t
feedback loo p with an i nternal transconductance
fid error amplifier, the AC lamp current is sensed by a
sense resistor (R1 3 in figure 3 on page 9)
connected in se ries with t he lo w voltag e termin al
a of CCFL la mp. The AC voltage a cross the sen se
resistor is fed into the CS p in. The peak voltage of
n sensed AC voltage is detected and compared with
a 1.25V internal refe rence voltage. The error is
o amplified that controls the on time of the full bridge
switches, as a result, the lamp current is regulated.
B the lamp current can be calculated by the following
equation:
l to Ilamp =
1.25V
2 Rsense
tia Lamp Fail Safe Functions
During normal operation, if the lamp is removed or
damaged, the voltage at CS pin will drops to 0V. If
n the peak voltage at CS pin cannot be regulated to
the predetermined value for more than 20ms, the
e inverter i s l atched shut down. Toggl ing ENA
restarts the operation.
fid Dimming Control
Three com monly used di mming mod es: analo g
n mode dimming, internal b urst mode dimming and
external b urst (PWM ) d imming fun ctions a re
o supported without any additional components. The
concurrent a nalog and b urst a chieves very wid e
C dimming range.
t DC volta ge ranging from 0V to 3V at ADIM pin
performs a nalog mod e dimming control. The
h voltage at ADIM pin modulates i nternal error
amplifier reference voltag e from 0.5V to 1.25V,
rig witch corresponds to a lamp current o
f
approximately 40% to 100%.
The BF/DM OD pin is u sed for internal/external
-Bburst mode selection and internal burst frequency
setting. External bu rst (P WM) dimming mod e is
nselected by shorting BF/DMOD pin to ground. The
OB3328 accepts an external low f requency PWM
O (LPWM) signal to DDIM pin with a voltage
Internal bu rst mode dimming is obt ained by
connecting a c apacitor to BF/DMOD pin. A low
frequency triangular waveform generator is formed
by the ca pacitor alon g wit h intern al co mparator,
internal current sou rce and current sink. Th e
triangular volt age waveform with p eak of 3V and
valley of 1V at this pi n is used for th e internal low
frequency burst PWM generation. its duty cycle so
as to lamp cu rrent is controlled by the DC volt age
at DDIM pin. The burst freque ncy F burst is set by
the following equation:
2000
Fburst (Hz) = CBF (nF)
A DC voltage rangin g from 0V to 3V at DIM pin
corresponds to a lamp c urrent of approximately
10% to 100%.
PIN\MODE Analog
Internal
Burst
External
LPWM
BF/DMOD -
DDIM -
ADIM 0-3V
Capacitor
0-3V
-
<0.5V
External
LPWM
-
The concurrent burst and analog dimming control
can achieves approximately 4% to 100% dimming
ratio.
swinging fro m less th an 0.8V to that of greate r
than 2.0V. The lamp brightness is controlled by the
duty cycle of the LPWM sign al. T he bu rst
© On-Bright Electronics
-9-
Confidential
OB_DO C_DS_2800
 

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