RangeMAX™
I N T E G R A T E D
P R O D U C T S
LX1688
M
ULTIPLE
L
AMP
CCFL C
ONTROLLER
DETAILED DESCRIPTION (C
ONTINUED
)
WWW .
Microsemi
.C
OM
and may or may not be externally synchronized to the
LCD video frame rate. It will directly gate the signal
BRT. CPWM should not be used in this case.
Fault Pin
The fault pin is a digital output that indicates that the
maximum numbers of strike attempts has occurred
without lamp ignition. In this condition the FAULT pin
will go active high with typically 20mA drive capability.
Holding the OLSNS pin low (<200mV) will also force
timeout and activate the FAULT pin. When used as a
master, fault condition true does not inhibit master clock
outputs PHA_SYNC and RMP_RST.
I_R Pin
The run mode frequency of the output is one half the
internal ramp frequency, which is proportional to a bias
current set by resistor R
I
of 80.6K. The output frequency
can thus be adjusted by varying the value of R
I-R
, the typical
range from about 50K to 100K. Since there is some
variation in the frequency due to change in the input supply
(VDD) it is recommended that the value of R
I-R
be selected
at the nominal input voltage.
Sleep Mode (ENABLE Signal) and Switched VDD
(VDDSW)
Since the LX1688 can be used in portable battery
operated systems, a very low power sleep mode is included.
The IC will consume less than 10µA quiescent current from
both the VDD and VDD_P pins combined, when the
ENABLE pin is deactivated. The polarity of the ENABLE
pin is programmable by the BEPOL input (see table 1). In
addition the controller provides a switched supply pin
VDDSW this output supplies at least 10mA at VDD
─
.2V
for external circuitry. This output can be used to power
additional circuitry that can be enabled with the controller.
BIAS & TIMING EQUATIONS
Formula 1:
Triangular Wave Generator Frequency, F
TRI
Formula 2:
Lamp Frequency (AOUT’s switching frequency), F
LAMP
F
TRI
=
Formula 3:
1
[Hz]
(25
×
R
I
×
C
TRI
)
Formula 4:
F
LAMP
=
1
[Hz]
200
e-
12
×
R
I
Minimum Current Error Amp Bandwidth, BW
IEA_MIN
Minimum Voltage Error Amp Bandwidth, B
WVEA_MIN
B
WIEA_MIN
=
Formula 5:
Softstart time, T
SS
0.000048
[Hz]
C
ICOMP
Formula 6:
B
WVEA_MIN
=
0
.
000048
[Hz]
C
VCOMP
Minimum Power-on Reset Pulse Width, T
MIN_POR
T
SS
=
4
,
500
,
000
×
C
VCOMP
[sec]
T
MIN_POR
=
2.3
e
6
×
C
POR
[sec]
D
ESCRIPTION
D
ESCRIPTION
Copyright
2001
Rev. 1.1a, 2003-03-21
Microsemi
Integrated Products, Power Management
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
MICROSEMI [ MICROSEMI CORPORATION ]
