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PDF LM2598T-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LM2598T-3.3 | |
| Descripción | SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator/ with Features | |
| Fabricantes | National Semiconductor | |
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March 1998
LM2598
SIMPLE SWITCHER® Power Converter 150 kHz
1A Step-Down Voltage Regulator, with Features
General Description
The LM2598 series of regulators are monolithic integrated
circuits that provide all the active functions for a step-down
(buck) switching regulator, capable of driving a 1A load with
excellent line and load regulation. These devices are avail-
able in fixed output voltages of 3.3V, 5V, 12V, and an adjust-
able output version.
This series of switching regulators is similar to the LM2595
series, with additional supervisory and performance features
added.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation†, improved line and load specifications,
fixed-frequency oscillator, Shutdown /Soft-start, error flag
delay and error flag output.
The LM2598 series operates at a switching frequency of 150
kHz thus allowing smaller sized filter components than what
would be needed with lower frequency switching regulators.
Available in a standard 7-lead TO-220 package with several
different lead bend options, and a 7-lead TO-263 surface
mount package. Typically, for output voltages less than 12V,
and ambient temperatures less than 50˚C, no heat sink is re-
quired.
A standard series of inductors (both through hole and sur-
face mount types) are available from several different manu-
facturers optimized for use with the LM2598 series. This fea-
ture greatly simplifies the design of switch-mode power
supplies.
Other features include a guaranteed ±4% tolerance on out-
put voltage under all conditions of input voltage and output
load conditions, and ±15% on the oscillator frequency. Ex-
ternal shutdown is included, featuring typically 85 µA
standby current. Self protection features include a two stage
current limit for the output switch and an over temperature
shutdown for complete protection under fault conditions.
Features
n 3.3V, 5V, 12V, and adjustable output versions
n Adjustable version output voltage range, 1.2V to 37V
±4% max over line and load conditions
n Guaranteed 1A output current
n Available in 7-pin TO-220 and TO-263 (surface mount)
package
n Input voltage range up to 40V
n Excellent line and load regulation specifications
n 150 kHz fixed frequency internal oscillator
n Shutdown /Soft-start
n Out of regulation error flag
n Error output delay
n Low power standby mode, IQ typically 85 µA
n High Efficiency
n Uses readily available standard inductors
n Thermal shutdown and current limit protection
Applications
n Simple high-efficiency step-down (buck) regulator
n Efficient pre-regulator for linear regulators
n On-card switching regulators
n Positive to Negative converter
Typical Application (Fixed Output Voltage Versions)
†Patent Number 5,382,918.
SIMPLE SWITCHER® and Switchers Made Simple® are registered trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS012593
DS012593-1
www.national.com
1 page  
All Output Voltage Versions
Electrical Characteristics (Continued)
Specifications with standard type face are
Range.
ILOAD =
Unless otherwise
200 mA
specified,
VIN
=
for TJ = 25˚C, and those with boldface type
12V for the 3.3V, 5V, and Adjustable version
apply over
and VIN =
full
24V
Operating Temperature
for the 12V version.
Symbol
Parameter
Conditions
LM2598-XX
Typ Limit
Units
(Limits)
(Note 4) (Note 5)
SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure 1
ISD Shutdown Current
VSHUTDOWN = 0.5V
5 µA
10 µA(max)
ISS Soft-start Current
VSoft-start = 2.5V
1.6 µA
5 µA(max)
FLAG/DELAY CONTROL Test Circuit of Figure 1
Regulator Dropout Detector Low (Flag ON)
96 %
Threshold Voltage
92 %(min)
98 %(max)
VFSAT
IFL
Flag Output Saturation
Voltage
Flag Output Leakage
Current
ISINK = 3 mA
VDELAY = 0.5V
VFLAG = 40V
0.3 V
0.7/1.0
V(max)
0.3 µA
Delay Pin Threshold
1.25 V
Voltage
Low (Flag ON)
1.21 V(min)
Delay Pin Source Current
High (Flag OFF) and VOUT Regulated
VDELAY = 0.5V
1.29 V(max)
3 µA
6 µA(max)
Delay Pin Saturation
Low (Flag ON)
55 mV
350/400 mV(max)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is in-
tended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Voltage internally clamped. If clamp voltage is exceeded, limit current to a maximum of 1 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely norm.
Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% pro-
duction tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to cal-
culate Average Outgoing Quality Level (AOQL).
Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2598
is used as shown in the Figure 1 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics.
Note 7: The switching frequency is reduced when the second stage current limit is activated. The amount of reduction is determined by the severity of current over-
load.
Note 8: No diode, inductor or capacitor connected to output pin.
Note 9: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 10: Feedback pin removed from output and connected to 12V for the 3.3V, 5V, and the ADJ. version, and 15V for the 12V version, to force the output transistor
switch OFF.
Note 11: VIN = 40V.
Note 12: Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board
with (1 oz.) copper area of approximately 1 in2.
Note 13: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 0.5 in2 of (1 oz.) copper area.
Note 14: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area.
Note 15: Junction to ambient thermal resistance with the TO-263 package tab soldered to a double sided printed circuit board with 3 in2 of (1 oz.) copper area on
the LM2598S side of the board, and approximately 16 in2 of copper on the other side of the p-c board. See application hints in this data sheet and the thermal model
in Switchers Made Simple® version 4.2 software.
5 www.national.com
5 Page 
LM2598 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version)
B. To simplify the capacitor selection procedure, refer to the
quick design component selection table shown in Figure 2.
This table contains different input voltages, output voltages,
and load currents, and lists various inductors and output ca-
pacitors that will provide the best design solutions.
C. The capacitor voltage rating for electrolytic capacitors
should be at least 1.5 times greater than the output voltage,
and often much higher voltage ratings are needed to satisfy
the low ESR requirements for low output ripple voltage .
D. For computer aided design software, see Switchers Made
Simple™ (version 4.2 or later).
3. Catch Diode Selection (D1)
A. The catch diode current rating must be at least 1.3 times
greater than the maximum load current. Also, if the power
supply design must withstand a continuous output short, the
diode should have a current rating equal to the maximum
current limit of the LM2598. The most stressful condition for
this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
C. This diode must be fast (short reverse recovery time) and
must be located close to the LM2598 using short leads and
short printed circuit traces. Because of their fast switching
speed and low forward voltage drop, Schottky diodes provide
the best performance and efficiency, and should be the first
choice, especially in low output voltage applications.
Ultra-fast recovery, or High-Efficiency rectifiers also provide
good results. Ultra-fast recovery diodes typically have re-
verse recovery times of 50 ns or less. Rectifiers such as the
1N5400 series are much too slow and should not be used.
EXAMPLE (Fixed Output Voltage Version)
B. From the quick design component selection table shown
in Figure 2, locate the 5V output voltage section. In the load
current column, choose the load current line that is closest to
the current needed in your application, for this example, use
the 1A line. In the maximum input voltage column, select the
line that covers the input voltage needed in your application,
in this example, use the 15V line. Continuing on this line are
recommended inductors and capacitors that will provide the
best overall performance.
The capacitor list contains both through hole electrolytic and
surface mount tantalum capacitors from four different capaci-
tor manufacturers. It is recommended that both the manufac-
turers and the manufacturer’s series that are listed in the
table be used.
In this example aluminum electrolytic capacitors from several
different manufacturers are available with the range of ESR
numbers needed.
220 µF 25V Panasonic HFQ Series
220 µF 25V Nichicon PL Series
C. For a 5V output, a capacitor voltage rating at least 7.5V or
more is needed. But, in this example, even a low ESR,
switching grade, 220 µF 10V aluminum electrolytic capacitor
would exhibit approximately 225 mΩ of ESR (see the curve
in Figure 16 for the ESR vs voltage rating). This amount of
ESR would result in relatively high output ripple voltage. To
reduce the ripple to 1% of the output voltage, or less, a ca-
pacitor with a higher voltage rating (lower ESR) should be se-
lected. A 16V or 25V capacitor will reduce the ripple voltage
by approximately half.
3. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 11. In this example, a
3A, 20V, 1N5820 Schottky diode will provide the best perfor-
mance, and will not be overstressed even for a shorted out-
put.
11 www.national.com
11 Page | ||
| Páginas | Total 33 Páginas | |
| PDF Descargar | [ Datasheet LM2598T-3.3.PDF ] | |
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