LT1786FCS#PBF Linear Technology, LT1786FCS#PBF Datasheet - Page 18

• Manufacturer Part Number: LT1786FCS#PBF
• Description: IC SW REG CCFL SMBUS PROG 16SOIC
• Manufacturer: Linear Technology

Specifications of LT1786FCS#PBF

• Applications: Converter, CCFL
• Voltage - Input: 4.5 ~ 30 V
• Number Of Outputs: 1
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Input Voltage: 30V
• Output Current: 1.9A
• No. Of Outputs: 1
• Supply Voltage Range: 3V To 6.5V
• No. Of Pins: 16
• Operating Temperature Range: 0°C To +70°C
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Filter Terminals: SMD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

LT1786F
TYPICAL
Dual Transformer CCFL Power Supply
Space constraints may dictate utilization of two small
transformers instead of a single, larger unit. Although this
approach is somewhat more expensive, it can solve space
problems and offers other attractive advantages. Figure
2’s approach is essentially a “grounded lamp” LT1786F-
based circuit. The transistors drive two transformer pri-
maries in parallel. The transformer secondaries, stacked
in series, provide the output. The relatively small trans-
formers, each supplying half the load power, may be
located directly at the lamp terminals. Aside from the
obvious space advantage (particularly height), this
arrangement minimizes parasitic wiring losses by elimi-
18
SHUTDOWN
APPLICATION
1 F
Figure 2. Dual Transformers Save Space and Minimize parasitic Losses While Maintaining
Current Accuracy and Line Regulation. Trade-Off Is Increased Cost
1000pF
1
2
3
4
5
6
7
8
PGND
I
DIO
V
AGND
SHDN
SMBSUS
ADR
CCFL
C
100k
220k
LT1786F
U
BAT54
ROYER
BULB
V
I
SDA
BAT
SCL
OUT
V
SW
IN
16
15
14
13
12
11
10
9
3
10
ZDT1048
0.1 F*
Q1-Q2
+
TO
SMBus
HOST
+
2
L2
2.2 F
6
2.2 F
16V
nating high voltage lead length. Additionally, although the
lamp receives differential drive, with its attendant low
parasitic losses, the feedback signal is ground referred.
Thus, the stacked secondaries afford floating lamp oper-
ating efficiency with grounded mode current certainty and
line regulation.
L1 is directly driven, with winding 4-5 furnishing feedback
in the normal fashion. L3, “slaved” to L1’s and L3’s
interconnects must be laid out for low inductance to
maintain waveform purity. The traces should be as wide as
possible (e.g., 1/8") and overlaid to cancel inductive
effects.
1
4
27pF
L1, L3 = COILTRONICS CTX110605
COILTRONICS [phone]
MBRS130L
L2 = COILTRONICS CTX100-4
* = WIMA MKI OR MKP-20
5
L1
= PANASONIC ECH-U
SEE TEXT AND NOTES
OVERLAY INDICATED TRACES BETWEEN L1 AND L3
LAMP
750
WIDE TRACE
WIDE TRACE
+V
V
5V
IN
BAT
3
0.1 F*
6
+
2
10
2.2 F
1
1786 F02
NC
4
5
NC
L3