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PDF LT1184F Data sheet ( Hoja de datos )
| Número de pieza | LT1184F | |
| Descripción | CCFL/LCD Contrast Switching Regulators | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1182/LT1183/LT1184/LT1184F
CCFL/LCD Contrast
Switching Regulators
FEATURES
s Wide Input Voltage Range: 3V to 30V
s Low Quiescent Current
s High Switching Frequency: 200kHz
s CCFL Switch : 1.25A, LCD Switch: 625mA
s Grounded or Floating Lamp Configurations
s Open-Lamp Protection
s Positive or Negative Contrast Capability
U
APPLICATIONS
s Notebook and Palmtop Computers
s Portable Instruments
s Automotive Displays
s Retail Terminals
DESCRIPTION
The LT®1182/LT1183 are dual current mode switching
regulators that provide the control function for Cold Cath-
ode Fluorescent Lighting (CCFL) and Liquid Crystal Display
(LCD) Contrast. The LT1184/LT1184F provide only the
CCFL function. The ICs include high current, high efficiency
switches, an oscillator, a reference, output drive logic,
control blocks and protection circuitry. The LT1182 per-
mits positive or negative voltage LCD contrast operation.
The LT1183 permits unipolar contrast operation and pins
out an internal reference. The LT1182/LT1183 support
grounded and floating lamp configurations. The LT1184F
supports grounded and floating lamp configurations. The
LT1184 supports only grounded lamp configurations. The
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
90% Efficient Floating CCFL Configuration with Dual Polarity LCD Contrast
ALUMINUM ELECTROLYTIC IS RECOMMENDED FOR C3B WITH AN
ESR ≥ 0.5Ω TO PREVENT DAMAGE TO THE LT1182 HIGH-SIDE
SENSE RESISTOR DUE TO SURGE CURRENTS AT TURN-ON.
C1 MUST BE A LOW LOSS CAPACITOR, C1 = WIMA MKP-20
Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001
UP TO 6mA
LAMP
10 6
C2
27pF
3kV
CCFL BACKLIGHT APPLICATION CIRCUITS CONTAINED IN THIS
DATA SHEET ARE COVERED BY U.S. PATENT NUMBER 5408162
AND OTHER PATENTS PENDING
L1
L1 = COILTRONICS CTX210605
L2 = COILTRONICS CTX100-4
L3 = COILTRONICS CTX02-12403
*DO NOT SUBSTITUTE COMPONENTS
C5
1000pF
R2
220k
3 2 1 45
+ C3B
2.2µF
35V
COILTRONICS (407) 241-7876
0µA TO 45µA ICCFL
CURRENT GIVES
0mA TO 6mA
BULB CURRENT.
THIS IS EQUAL TO
0% TO 90% DUTY
CYCLE FOR THE
PWM SIGNAL.
D5
BAT85
R4
46.4k
V (PWM) 1%
0V TO 5V
1kHz PWM C6 +
2.2µF
R5, 43.2k, 1%
C7, 1µF
C1*
0.068µF
R3
100k Q2*
Q1*
1 CCFL
PGND
2
ICCFL
16
CCFL VSW
15
BULB
3
DIO
14
BAT
4
LT1182
13
CCFL VC
ROYER
L2
100µH
D1
1N5818
5
AGND
12
VIN
SHUTDOWN
C8, 0.68µF
6
7
R7, 10K 8
SHDN
LCD VC
LCD
PGND
11
FBP
10
FBN
9
LCD VSW
R9, 4.99k, 1%
+ C3A
2.2µF
35V
R1
750Ω
+ C12
2.2µF
35V
BAT
8V TO 28V
EITHER NEGCON OR POSCON
MUST BE GROUNDED.
GROUNDING NEGCON GIVES
VARIABLE POSITIVE CONTRAST
FROM 10V TO 30V.
GROUNDING POSCON GIVES
VARIABLE NEGATIVE CONTRAST
FROM –10V TO – 30V.
D3 L3
1N5934A
24V 4
6 C11 +
22µF
D2 2
1N914
9 35V
+
C9, 0.01µF
VIN
≥ 3V
C4
2.2µF
N = 1:2 D4
1N914
R12
20k
R13
8.45k
1%
C10
0.01µF
R14
1.21k
1%
POSCON
NEGCON
R10, 10k, 1% R11, 20k, 1%
5V
1182/3 TA01
1
1 page  
LT1182/LT1183/LT1184/LT1184F
TYPICAL PERFORMANCE CHARACTERISTICS
LT1182/LT1183 Supply Current
vs Temperature
14
13
12
11
10
VIN = 30V
9
VIN = 3V
8
7
6
5
4
–75 – 50 – 25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 G01
Shutdown Input Bias Current
vs Temperature
6
5
4
VIN = 30V
VIN = 5V
3
2 VIN = 3V
1
0
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 G04
CCFL Duty Cycle vs Temperature
95
93
91
89
87
85
83
81
79
77
75
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 • G07
LT1184/LT1184F Supply Current
vs Temperature
10
9
8
7
6 VIN = 30V
5 VIN = 3V
4
3
2
1
0
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 G02
Shutdown Threshold Voltage
vs Temperature
1.2
1.1
1.0
0.9
0.8
0.7
0.6
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 G05
LCD Frequency vs Temperature
240
230
220
210 VIN = 30V
200
VIN = 3V
190
180
170
160
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 • G08
Shutdown Current
vs Temperature
100
90
8O
VIN = 30V
70
60
50
40 VIN = 5V
30
VIN = 3V
20
10
0
–75 –50 – 25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 G03
CCFL Frequency vs Temperature
240
230
220
210 VIN = 30V
200
VIN = 3V
190
180
170
160
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 • G06
LCD Duty Cycle vs Temperature
95
93
91
89
87
85
83
81
79
77
75
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
LT1182 • G09
5
5 Page 
LT1182/LT1183/LT1184/LT1184F
PIN FUNCTIONS
Bulb (Pin 15): This pin connects to the low side of a 7V
threshold comparator between the BAT and Bulb pins.
This circuit sets the maximum voltage level across the
primary side of the Royer converter under all operating
conditions and limits the maximum secondary output
under start-up conditions or open lamp conditions. This
eases transformer voltage rating requirements. Set the
voltage limit to insure lamp start-up with worst-case, lamp
start voltages and cold-temperature system operating
conditions. The Bulb pin connects to the junction of an
external divider network. The divider network connects
from the center tap of the Royer transformer or the actual
battery supply voltage to the top side of the current source
“tail inductor”. A capacitor across the top of the divider
network filters switching ripple and sets a time constant
that determines how quickly the clamp activates. When
the comparator activates, sink current is generated to pull
the CCFL VC pin down. This action transfers the entire
regulator loop from current mode operation into voltage
mode operation.
BAT (Pin 14): This pin connects to the battery or battery
charger voltage from which the CCFL Royer converter and
LCD contrast converter operate. This voltage is typically
higher than the VIN supply voltage but can be equal or less
than VIN. However, the BAT voltage must be at least 2.1V
greater than the internal 2.4V regulator or 4.5V minimum
up to 30V maximum. This pin provides biasing for the
lamp current programming block, is used with the Royer
pin for floating lamp configurations, and connects to one
input for the open lamp protection circuitry. For floating
lamp configurations, this pin is the noninverting terminal
of a high-side current sense amplifier. The typical quies-
cent current is 50µA into the pin. The BAT and Royer pins
monitor the primary side Royer converter current through
an internal 0.1Ω top side current sense resistor. A 0A to 1A
primary side, center tap converter current is translated to
an input signal range of 0mV to 100mV for the current
sense amplifier. This input range translates to a 0µA to
500µA sink current at the CCFL VC pin that nulls against the
source current provided by the programmer circuit. The
BAT pin also connects to the top side of an internal clamp
between the BAT and Bulb pins.
Royer (Pin 13): This pin connects to the center-tapped
primary of the Royer converter and is used with the BAT
pin in a floating lamp configuration where lamp current is
controlled by sensing Royer primary side converter cur-
rent. This pin is the inverting terminal of a high-side
current sense amplifier. The typical quiescent current is
50µA into the pin. If the CCFL regulator is not used in a
floating lamp configuration, tie the Royer and BAT pins
together. This pin is only available on the LT1182/LT1183/
LT1184F.
VIN (Pin 12): This pin is the supply pin for the LT1182/
LT1183/LT1184/LT1184F. The ICs accept an input voltage
range of 3V minimum to 30V maximum with little change
in quiescent current (zero switch current). An internal,
low dropout regulator provides a 2.4V supply for most of
the internal circuitry. Supply current increases as switch
current increases at a rate approximately 1/50 of switch
current. This corresponds to a forced Beta of 50 for each
switch. The ICs incorporate undervoltage lockout by sens-
ing regulator dropout and lockout switching for input
voltages below 2.5V. Hysteresis is not used to maximize
the useful range of input voltage. The typical input voltage
is a 3.3V or 5V logic supply.
LT1182/LT1183
LCD VC (Pin 7): This pin is the output of the LCD contrast
error amplifier and the input of the current comparator for
the LCD contrast regulator. Its uses include frequency
compensation and current limiting. The voltage on the
LCD VC pin determines the current trip level for switch
turnoff. During normal operation, this pin sits at a voltage
between 0.95V (zero switch current) and 2.0V (maximum
switch current). The LCD VC pin has a high impedance
output and permits external voltage clamping to adjust
current limit. A series R/C network to ground provides
stable loop compensation.
LCD PGND (Pin 8): This pin is the emitter of an internal
NPN power switch. LCD contrast switch current flows
through this pin and permits internal, switch-current
sensing. The regulators provide a separate analog ground
and power ground(s) to isolate high current ground paths
from low current signal paths. Linear Technology recom-
mends star-ground layout techniques.
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT1184F.PDF ] | |
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