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PDF LM2588 Data sheet ( Hoja de datos )
| Número de pieza | LM2588 | |
| Descripción | SIMPLE SWITCHER 5A Flyback Regulator with | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM2588 (archivo pdf) en la parte inferior de esta página. Total 29 Páginas | ||
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April 1998
LM2588
SIMPLE SWITCHER® 5A Flyback Regulator with
Shutdown
General Description
The LM2588 series of regulators are monolithic integrated
circuits specifically designed for flyback, step-up (boost), and
forward converter applications. The device is available in 4
different output voltage versions: 3.3V, 5.0V, 12V, and adjust-
able.
Requiring a minimum number of external components, these
regulators are cost effective, and simple to use. Included in
the datasheet are typical circuits of boost and flyback regula-
tors. Also listed are selector guides for diodes and capacitors
and a family of standard inductors and flyback transformers
designed to work with these switching regulators.
The power switch is a 5.0A NPN device that can stand-off
65V. Protecting the power switch are current and thermal
limiting circuits, and an undervoltage lockout circuit. This IC
contains an adjustable frequency oscillator that can be pro-
grammed up to 200 kHz. The oscillator can also be synchro-
nized with other devices, so that multiple devices can oper-
ate at the same switching frequency.
Other features include soft start mode to reduce in-rush cur-
rent during start up, and current mode control for improved
rejection of input voltage and output load transients and
cycle-by-cycle current limiting. The device also has a shut-
down pin, so that it can be turned off externally. An output
voltage tolerance of ±4%, within specified input voltages and
output load conditions, is guaranteed for the power supply
system.
Features
n Requires few external components
n Family of standard inductors and transformers
n NPN output switches 5.0A, can stand off 65V
n Wide input voltage range: 4V to 40V
n Adjustable switching frequency: 100 kHz to 200 kHz
n External shutdown capability
n Draws less than 60 µA when shut down
n Frequency synchronization
n Current-mode operation for improved transient
response, line regulation, and current limit
n Internal soft-start function reduces in-rush current during
start-up
n Output transistor protected by current limit, under
voltage lockout, and thermal shutdown
n System output voltage tolerance of ±4% max over line
and load conditions
Typical Applications
n Flyback regulator
n Forward converter
n Multiple-output regulator
n Simple boost regulator
Flyback Regulator
SIMPLE SWITCHER® and Switchers Made Simple ® are registered trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS012420
DS012420-1
www.national.com
1 page  
LM2588-ADJ
Electrical Characteristics (Continued)
Specifications with standard type face are
Range. Unless otherwise specified, VIN =
for TJ
5V.
=
25˚C,
and
those
in
bold
type
face
apply
over
full
Operating
Temperature
Symbol
Parameters
Conditions
Typical
Min
Max
Units
UNIQUE DEVICE PARAMETERS (Note 5)
VREF
∆VREF
Output Reference
Voltage
Reference Voltage
Line Regulation
Measured at Feedback Pin
VCOMP = 1.0V
VIN = 4V to 40V
1.230
1.5
1.208/1.205
1.252/1.255
V
mV
GM
AVOL
IB
Error Amp
Transconductance
Error Amp
Voltage Gain
Error Amp
Input Bias Current
ICOMP = −30 µA to +30 µA
VCOMP = 1.0V
VCOMP = 0.5V to 1.6V
RCOMP = 1.0 MΩ (Note 6)
VCOMP = 1.0V
3.200
670
125
1.800
400/200
6.000
425/600
mmho
V/V
nA
All Output Voltage Versions
Electrical Characteristics (Note 5)
Specifications with standard type face are
Range. Unless otherwise specified, VIN =
for TJ
5V.
=
25˚C,
and
those
in
bold
type
face
apply
over
full
Operating
Temperature
Symbol
Parameters
Conditions
Typical
Min
Max
Units
IS Input Supply Current Switch Off
(Note 8)
11
15.5/16.5
mA
ISWITCH = 3.0A
IS/D
Shutdown Input
VSH = 3V
Supply Current
85
16
140/165
100/300
mA
µA
VUV Input Supply
Undervoltage
Lockout
RLOAD = 100Ω
3.30
3.05
3.75 V
fO Oscillator Frequency Measured at Switch Pin
RLOAD = 100Ω, VCOMP = 1.0V
100
85/75
115/125
kHz
Freq. Adj. Pin Open (Pin 1)
fSC
VEAO
Short-Circuit
Frequency
Error Amplifier
Output Swing
RSET = 22 kΩ
Measured at Switch Pin
RLOAD = 100Ω
VFEEDBACK = 1.15V
Upper Limit
(Note 7)
200
25
2.8 2.6/2.4
kHz
kHz
V
Lower Limit
0.25
0.40/0.55
V
(Note 8)
IEAO
Error Amp
Output Current
(Note 9)
165 110/70
260/320
µA
(Source or Sink)
ISS
DMAX
Soft Start Current
Maximum Duty
Cycle
VFEEDBACK = 0.92V
VCOMP = 1.0V
RLOAD = 100Ω
(Note 7)
11.0
98
8.0/7.0
93/90
17.0/19.0
µA
%
IL
VSUS
Switch Leakage
Current
Switch Sustaining
Voltage
Switch Off
VSWITCH = 60V
dV/dT = 1.5V/ns
15
300/600
µA
65 V
5 www.national.com
5 Page 
Block Diagram
For Fixed Versions
3.3V, R1 = 3.4k, R2 = 2k
5.0V, R1 = 6.15k, R2 = 2k
12V, R1 = 8.73k, R2 = 1k
For Adj. Version
R1 = Short (0Ω), R2 = Open
FIGURE 3.
DS012420-23
Flyback Regulator Operation
The LM2588 is ideally suited for use in the flyback regulator
topology. The flyback regulator can produce a single output
voltage, such as the one shown in Figure 4, or multiple out-
put voltages. In Figure 4, the flyback regulator generates an
output voltage that is inside the range of the input voltage.
This feature is unique to flyback regulators and cannot be
duplicated with buck or boost regulators.
The operation of a flyback regulator is as follows (refer to
Figure 4): when the switch is on, current flows through the
primary winding of the transformer, T1, storing energy in the
magnetic field of the transformer. Note that the primary and
secondary windings are out of phase, so no current flows
through the secondary when current flows through the pri-
mary. When the switch turns off, the magnetic field col-
lapses, reversing the voltage polarity of the primary and sec-
ondary windings. Now rectifier D1 is forward biased and
current flows through it, releasing the energy stored in the
transformer. This produces voltage at the output.
The output voltage is controlled by modulating the peak
switch current. This is done by feeding back a portion of the
output voltage to the error amp, which amplifies the differ-
ence between the feedback voltage and a 1.230V reference.
The error amp output voltage is compared to a ramp voltage
proportional to the switch current (i.e., inductor current dur-
ing the switch on time). The comparator terminates the
switch on time when the two voltages are equal, thereby
controlling the peak switch current to maintain a constant
output voltage.
11 www.national.com
11 Page | ||
| Páginas | Total 29 Páginas | |
| PDF Descargar | [ Datasheet LM2588.PDF ] | |
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