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PDF LT1424CN8-9 Data sheet ( Hoja de datos )
| Número de pieza | LT1424CN8-9 | |
| Descripción | Isolated Flyback Switching Regulator with 9V Output | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT1424-9
Isolated Flyback
Switching Regulator
with 9V Output
FEATURES
s No Transformer “Third Winding” or Optoisolator
Required
s Application Circuit Meets PCMCIA Type II
Height Requirement
s Fixed, Application Specific 9V Output Voltage
s Regulation Maintained Well into Discontinuous
Mode (Light Load)
s Load Compensation Provides Excellent
Load Regulation
s Available in 8-Pin PDIP and SO Packages
s Operating Frequency: 285kHz
U
APPLICATIO S
s Ethernet Isolated 5V to – 9V Converter
DESCRIPTIO
The LT®1424-9 is a monolithic high power switching
regulator specifically designed for the isolated flyback
topology. No “third winding” or optoisolator is required;
the integrated circuit senses the isolated output voltage
directly from the primary side flyback waveform. A high
current, high efficiency switch is included on the die along
with all oscillator, control and protection circuitry.
The LT1424-9 operates with input supply voltages from
3V to 20V and draws only 7mA quiescent current. It can
deliver up to 200mA at 9V with no external power devices.
By utilizing current mode switching techniques, it pro-
vides excellent AC and DC line regulation.
The LT1424-9 has a number of features not found on other
switching regulator ICs. Its unique control circuitry can
maintain regulation well into discontinuous mode. Load
compensation circuitry allows for improved load regula-
tion. An externally activated shutdown mode reduces total
supply current to 20µA typical for standby operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
5V
INPUT
COM
– 9V PCMCIA Type II Isolated LAN Supply
(2.41mm Maximum Component Height)
C1
10µF
25V
C2
10µF
25V
100k
1000pF
0.1µF
47pF
LT1424-9
2
VC
1
SHDN
3 SYNC
4 SGND
8
RCCOMP
7
VIN
6
VSW
5
PGND
ISOLATION
BARRIER
C6
R2 220pF
75Ω
D1 R1 MBRS130LT3
1N5248
75Ω
OUT
COM
C5
220pF
13
C3 C4 1.8k
D2
MBR0540T4
T1
10µF
10µF
25V 25V
24
– 9V
200mA
1:1 1424 TA01
0.1µF
C1, C2, C3, C4: MARCON THCS50E1E106Z CERAMIC
CAPACITOR, SIZE 1812. (847) 696-2000
T1: COILTRONICS CTX02-13483
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
Minimum Switch On Time
vs Temperature
275
250
225
200
175
150
125
100
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
1424-9 G10
Flyback Enable Delay Time
vs Temperature
250
225
200
175
150
125
100
75
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
1424-9 G11
LT1424-9
Minimum Flyback Enable Time
vs Temperature
275
250
225
200
175
150
125
100
– 50 – 25
0 25 50 75
TEMPERATURE (°C)
100 125
1424-9 G12
PIN FUNCTIONS
SHDN (Pin 1): Shutdown. This pin is used to turn off the
regulator and reduce VIN input current to a few tens of
microamperes. The SHDN pin can be left floating when
unused.
VC (Pin 2): Control Voltage. This pin is the output of the
feedback amplifier and the input of the current compara-
tor. Frequency compensation of the overall loop is effected
by placing a capacitor between this node and ground.
SYNC (Pin 3): Pin to synchronize internal oscillator to
external frequency reference. It is directly logic compat-
ible and can be driven with any signal between 10% and
90% duty cycle. If unused, this pin should be tied to
ground.
SGND (Pin 4): Signal Ground. This pin is a clean ground.
The internal reference and feedback amplifier are referred
to it. Keep the ground path connection to the VC compen-
sation capacitor free of large ground currents.
PGND (Pin 5): Power Ground. This pin is the emitter of the
power switch device and has large currents flowing through
it. It should be connected directly to a good quality ground
plane.
VSW (Pin 6): This is the collector node of the output switch
and has large currents flowing through it. Keep the traces
to the switching components as short as possible to
minimize electromagnetic radiation and voltage spikes.
VIN (Pin 7): Supply Voltage. Bypass input supply pin with
10µF or more. The part goes into undervoltage lockout
when VIN drops below 2.8V. Undervoltage lockout stops
switching and pulls the VC pin low.
RCCOMP (Pin 8): Pin for the External Filter Capacitor for
Load Compensation Function. A common 0.1µF
ceramic capacitor will suffice.
5
5 Page 
U
OPERATION
) )∆VRCCOMP
∆ISW
= Data sheet value for RCCOMP pin
action vs switch current
RFB = External “feedback” resistor value
ROUT = Uncompensated output impedance
LT1424-9
) )) )∆VOUT
∆IOUT
= K1
∆VRCCOMP
∆ISW
RFB
ROCOMP
Nominal output impedance cancellation is obtained by
equating this expression with ROUT.
APPLICATIONS INFORMATION
The LT1424-X is an application-specific 8-pin part which
implements an isolated flyback switcher/controller. Three
on-chip thin-film resistors are used to “program” the part
for a specific application including mainly desired output
voltage, transformer turns ratio and secondary circuit ESR
behavior. As of Initial Release, the LT1424-9 is available
which implements the “– 9V PCMCIA II Isolated LAN
Supply” as described in the Typical Application section.
Potential users with a high volume requirement for other
applications are advised as follows: general experimenta-
tion/breadboarding may be done with the LT1425. This is
a general purpose 16-pin part whose functionality is
similar to the LT1424-X, with the exception that the three
application resistors are external user-supplied compo-
nents. Application information relating to the proper
selection of these resistor values is contained within the
LT1425 data sheet. Once technical feasibility is demon-
strated, the potential user may discuss the possibility of an
additional LT1424-X version with the factory.
OUTPUT VOLTAGE ERROR SOURCES
Conventional nonisolated switching power supply ICs
typically have only two substantial sources of output
voltage error— the internal or external resistor divider
network that connects to VOUT and the internal IC refer-
ence. The LT1424-9, which senses the output voltage in
both a dynamic and an isolated manner, exhibits addi-
tional potential error sources to contend with. Some of
these errors are proportional to output voltage, others are
fixed in an absolute millivolt sense. Here is a list of possible
error sources and their effective contribution:
Internal Voltage Reference
The internal bandgap voltage reference is, of course,
imperfect. Its error, both at 25°C and over temperature is
already included in the specifications for Reference
Voltage.
Schottky Diode Drop
The LT1424-9 senses the output voltage from the trans-
former primary side during the flyback portion of the cycle.
This sensed voltage therefore includes the forward drop,
VF, of the rectifier (usually a Schottky diode). Lot-to-lot
and ambient temperature variations will show up as output
voltage shift/drift.
Secondary Leakage Inductance
Leakage inductance on the transformer secondary
reduces the effective primary-to-secondary turns ratio
(NP/NS) from its ideal value. This increases the output
voltage target by a similar percentage and has been
nominally taken into account in the design of the
LT1424-9. To the extent that secondary leakage induc-
tance varies from part-to-part, the output voltage will be
affected.
Output Impedance Error
The LT1424-9 contains a load compensation function to
provide a nominal, first-order cancellation of the effects
of secondary circuit ESR. Unit-to-unit variation plus
some inherent nonlinearity in the cancellation results in
some residual VOUT variation with load.
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1424CN8-9.PDF ] | |
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