KIA3802F
PIN DESCRIPTION
NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Symbol
ENABLE
CMP
SST
CT
RT
LCT
V
DIM
LPWM
OUT1
GND
OUT2
V
CC
OVP
V
REF
Timer
IN-
I/O
I
I
I
I
I
I
I
O
O
I
O
I
I
O
I
I
Enable input.
Compensation output of the error amplifier.
Soft-start Capacitor.
Timing capacitor.
Timing resistor set operating frequency.
Triangular wave for burst-mode dimming; frequency.
Input analog signal for burst-mode dimming control.
Low-frequency PWM signal for burst-mode dimming control.
Output 1.
Ground.
Output 2.
Voltage source for the IC.
Output voltage sense; Vth=2V.
Reference voltage output ; 5V typical.
Capacitor for CCFL ignition duration.
Inverting input.
Description
MAXIMUM RATING (Ta = 25
Rating
Power Supply Voltage
Power Dissipation(Ta=25 )
Output Current
Operating Temp.
Storage Temp.
, unless otherwise noted.)
Symbol
V
CC
P
D
I
O(MAX)
T
opr
T
stg
Limits
20
400
50
-20 ~ 85
-55 ~ 150
Unit
V
mW
mA
RECOMMENDED OPERATING CONDITIONS
Rating
Power Supply Voltage
Oscillation Frequency
Timing Resister
Symbol
V
CC
f
OSC
RT
Limits
7 ~ 20
30 ~ 200
3 ~ 30
Unit
V
KHz
2005.12.6
Revision No : 0
2/5
KIA3802F
Functional Description
1) Main Frequency (Lamp Operation Frequency)
A resistor RT and a capacitor CT determine the main frequency of
IC. The main frequency can be calculated as below equation:
critical factors.
1). Estimating Minimum Primary Voltage.
The minimum primary voltage is obtained from the value of the low
supply voltage.
2). Estimating Maximum Secondary Voltage.
The secondary is composed of a ballast capacitor, a voltage divide
capacitor and the lamp parasitic capacitor.
The voltage across the ballast capacitor can be calculated as below
equation:
Main
f
[kHz] =
6.8 10
2
CT[nF] RT[k
Ω
]
2) Open Lamp Protection
Open lamp protection in the ignition time is provided through both
OVP and TIMER pin to ensure a rated voltage is achieved and a
required timing is satisfied.
If time that TIMER capacitor charges to 3V is long than the CCFL
ignition time, it can prevent over-operating by protection circuit.
3) Error Amplifier
The CCFL current is regulated through the error amplifier. Error
amplifier output (CMP) voltage and ramp wave (CT) make the
PWM pulses. The non-inverting reference is at 2.5V nominal.
4) OVP
When the output voltage reaches the threshold, it commands the
PWM controller to maintain the current driving level. This ensures
that output gets sufficient striking voltage while operating the power
transformer safely. The OVP threshold is set at 2V nominal.
5) On/Off Function
The Enable pin provides the function to turn on and off the output
without shut down the supply voltage. The threshold of the Enable is
set at 2.0V.
6) Soft-start
The soft-start function is provided with a capacitor connected to SST
pin. It provides a rate of rise for the pulse width where switches are
turned on. A 2.2 capacitor connected on the SST pin can set a 0.4
second period for striking the lamp.
7) Burst-mode Dimming
The burst-mode frequency is determined by a capacitor connected to
LCT pin.
The frequency can be calculated by:
V
Ballast C
= X
Ballast
I
Lamp
The maximum secondary voltage can be calculated as below
equation:
Vsecondary =
Transformer turns ratio is:
V
Lamp2
+
V
Ballast C2
V
secondary
V
primary
N=
2. Required Number of Secondary Turns
From the core constant provided by the core manufacturer, you will
need the effective core cross sectional area(Ae).
From the Faraday's law, the required number of secondary turns
would be:
N
secondary
=
V
secondary
t
max
10
8
B A
e
3. Required Number of Primary Turns
From the turns ratio and number of secondary turns
Nprimary
=
4. Determination of Wire Gauge
N
secondary
N
Wire gauge can be done by an acceptable current density.
From the assumed current density (500cmil) and the current that
flows through wires, the required Circular Mils is:
1 10
6
f [Hz] =
LCT[nF] RT[k
Ω
]
To compare the input of V
DIM
pin with the ramp wave(LCT) makes
the PWM pulses for Burst-mode Dimming. The LPWM pin is pulled
to V
REF
to make the dark portion of the CCFL output burst and the
floating state to make the bright portion. A less than 0.6V input on
V
DIM
pin will obtain 100% brightness.
Cmils = C
DLim
I
RMS
From the AWG table, pick a wire-gauge that would fit limit.
Using the selected wire diameter and bobbin information, determine
if this wire gauge will fit in the space allotted. (when the space
factor[SF] is accounted for)
Transformer Design
1. Transformer Turns Ratio
Calculation of the required turns ratio involves the estimation of two
2005.12.6
Revision No : 0
5/5
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