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PDF LM2595 Data sheet ( Hoja de datos )
| Número de pieza | LM2595 | |
| Descripción | SIMPLE SWITCHER Power Converter 150 kHz 1A Step-Down Voltage Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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May 1999
LM2595
SIMPLE SWITCHER® Power Converter 150 kHz
1A Step-Down Voltage Regulator
General Description
The LM2595 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.
Requiring a minimum number of external components, these
regulators are simple to use and include internal frequency
compensation†, and a fixed-frequency oscillator.
The LM2595 series operates at a switching frequency of
150 kHz thus allowing smaller sized filter components than
what would be needed with lower frequency switching regu-
lators. Available in a standard 5-lead TO-220 package with
several different lead bend options, and a 5-lead TO-263
surface mount package. Typically, for output voltages less
than 12V, and ambient temperatures less than 50˚C, no heat
sink is required.
A standard series of inductors are available from several dif-
ferent manufacturers optimized for use with the LM2595 se-
ries. This feature greatly simplifies the design of
switch-mode power supplies.
Other features include a guaranteed ±4% tolerance on out-
put voltage under specified input voltage and output load
conditions, and ±15% on the oscillator frequency. External
shutdown is included, featuring typically 85 µA stand-by cur-
rent. Self protection features include a two stage frequency
reducing current limit for the output switch and an over tem-
perature shutdown for complete protection under fault condi-
tions.
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 Available in TO-220 and TO-263 (surface mount)
packages
n Guaranteed 1A output load current
n Input voltage range up to 40V
n Requires only 4 external components
n Excellent line and load regulation specifications
n 150 kHz fixed frequency internal oscillator
n TTL shutdown capability
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
Note: † Patent Number 5,382,918.
Typical Application (Fixed Output Voltage Versions)
DS012565-1
SIMPLE SWITCHER® and Switchers Made Simple® are registered trademarks of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS012565
www.national.com
1 page  
All Output Voltage Versions
Electrical Characteristics (Continued)
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Operating Tempera-
24V for the 12V ver-
Symbol
Parameter
Conditions
LM2595-XX
Typ Limit
Units
(Limits)
(Note 3) (Note 4)
ON/OFF CONTROL Test Circuit Figure 1
IH ON/OFF Pin
Input Current
VLOGIC = 2.5V (Regulator OFF)
5 µA
15 µA(max)
IL
VLOGIC = 0.5V (Regulator ON)
0.02
µA
5 µA(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: The human body model is a 100 pF capacitor discharged through a 1.5k resistor into each pin.
Note 3: Typical numbers are at 25˚C and represent the most likely norm.
Note 4: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% produc-
tion tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate
Average Outgoing Quality Level (AOQL).
Note 5: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator sys-
tem performance. When the LM2595 is used as shown in the Figure 1 test circuit, system performance will be as shown in system parameters section of Electrical
Characteristics.
Note 6: 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 7: No diode, inductor or capacitor connected to output pin.
Note 8: Feedback pin removed from output and connected to 0V to force the output transistor switch ON.
Note 9: 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 10: VIN = 40V.
Note 11: 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 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in2 of (1 oz.) copper area.
Note 13: 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 14: 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 LM2595S side of the board, and approximately 16 in2 of copper on the other side of the p-c board. See Application Information in this data sheet and the thermal
model in Switchers Made Simple® version 4.3 software.
Typical Performance Characteristics (Circuit of Figure 1)
Normalized
Output Voltage
Line Regulation
Efficiency
DS012565-11
DS012565-12
5
DS012565-13
www.national.com
5 Page 
LM2595 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
Conditions
Inductor
Output
Voltage
(V)
3.3
5
12
Load
Current
(A)
1
0.5
1
0.5
1
0.5
Max Input
Voltage
(V)
5
7
10
40
6
10
40
8
10
15
40
9
20
40
15
18
30
40
15
20
40
Inductance
(µH)
22
33
47
68
47
68
100
33
47
68
100
68
150
150
47
68
150
220
68
150
330
Inductor
(#)
L24
L23
L31
L30
L13
L21
L20
L28
L31
L30
L29
L21
L19
L19
L31
L30
L36
L35
L21
L19
L26
Output Capacitor
Through Hole Electrolytic Surface Mount Tantalum
Panasonic Nichicon AVX TPS
Sprague
HFQ Series PL Series
Series
595D Series
(µF/V)
(µF/V)
(µF/V)
(µF/V)
330/16
330/16
220/10
330/10
270/25
270/25
220/10
270/10
220/25
220/35
220/10
220/10
180/35
220/35
220/10
180/10
220/25
220/16
220/10
220/10
150/35
150/25
100/16
150/16
150/35
82/35
100/16
100/20
330/16
330/16
220/10
270/10
220/25
220/25
220/10
220/10
180/35
180/35
220/10
150/16
180/35
120/35
100/16
120/16
180/16
180/16
220/10
150/16
120/25
1200/25
100/16
100/20
100/25
100/25
68/20
68/25
220/25
220/25
68/20
120/20
180/35
120/25
68/20
120/20
82/25
82/25
68/20
100/20
82/25
82/25
68/20
68/25
180/25
180/25
68/20
120/20
82/25
82/25
68/20
100/20
56/25
56/25
68/20
68/25
FIGURE 2. LM2595 Fixed Voltage Quick Design Component Selection Table
LM2595 Series Buck Regulator Design Procedure (Adjustable Output)
PROCEDURE (Adjustable Output Voltage Version)
Given:
VOUT = Regulated Output Voltage
VIN(max) = Maximum Input Voltage
ILOAD(max) = Maximum Load Current
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 1)
Use the following formula to select the appropriate resistor
values.
EXAMPLE (Adjustable Output Voltage Version)
Given:
VOUT = 20V
VIN(max) = 28V
ILOAD(max) = 1A
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 1)
Select R1 to be 1 kΩ, 1%. Solve for R2.
Select a value for R1 between 240Ω and 1.5 kΩ. The lower
resistor values minimize noise pickup in the sensitive feed-
back pin. (For the lowest temperature coefficient and the best
stability with time, use 1% metal film resistors.)
R2 = 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 kΩ.
R2 = 15.4 kΩ.
Procedure continued on next page.
Example continued on next page.
11
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| Páginas | Total 29 Páginas | |
| PDF Descargar | [ Datasheet LM2595.PDF ] | |
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