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PDF LM2597M-3.3 Data sheet ( Hoja de datos )

Número de pieza LM2597M-3.3
Descripción SIMPLE SWITCHER Power Converter 150 kHz 0.5A Step-Down Voltage Regulator/ with Features
Fabricantes National Semiconductor 
Logotipo National Semiconductor Logotipo



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March 1998
LM2597/LM2597HV
SIMPLE SWITCHER® Power Converter 150 kHz 0.5A
Step-Down Voltage Regulator, with Features
General Description
The LM2597/LM2597HV series of regulators are monolithic
integrated circuits that provide all the active functions for a
step-down (buck) switching regulator, capable of driving a
0.5A load with excellent line and load regulation. These de-
vices are available in fixed output voltages of 3.3V, 5V, 12V,
and an adjustable output version, and are packaged in an
8-lead DIP and an 8-lead surface mount package.
This series of switching regulators is similar to the LM2594
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 LM2597/LM2597HV series operates at a switching fre-
quency of 150 kHz thus allowing smaller sized filter compo-
nents than what would be needed with lower frequency
switching regulators. Because of its high efficiency, the cop-
per traces on the printed circuit board are normally the only
heat sinking needed.
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 LM2597/LM2597HV 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 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.
The LM2597HV is for use in applications requiring and input
voltage up to 60V.
Features
n 3.3V, 5V, 12V, and adjustable output versions
n Adjustable version output voltage range, 1.2V to 37V
(57V for HV version)±4% max over line and load
conditions
n Guaranteed 0.5A output current
n Available in 8-pin surface mount and DIP-8 package
n Input voltage range up to 60V
n 150 kHz fixed frequency internal oscillator
n Shutdown /Soft-start
n Out of regulation error flag
n Error output delay
n Bias Supply Pin (VBS) for internal circuitry improves
efficiency at high input voltages
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 DS012440
DS012440-1
www.national.com

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LM2597M-3.3 pdf
All Output Voltage Versions
Electrical Characteristics (Continued)
Note 6: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2597/
LM2597HV is used as shown in the Figure 12 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 for the LM2597 and 60V for the LM2597HV.
Note 12: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will
lower thermal resistance further. See application hints in this data sheet and the thermal model in Switchers Made Simple software.
Typical Performance Characteristics
Normalized
Output Voltage
Line Regulation
Efficiency
Switch Saturation
Voltage
DS012440-2
DS012440-3
Switch Current Limit
Dropout Voltage
DS012440-4
Quiescent Current
DS012440-5
Standby
Quiescent Current
DS012440-6
DS012440-7
Minimum Operating
Supply Voltage
DS012440-8
DS012440-9
5
DS012440-10
www.national.com

5 Page





LM2597M-3.3 arduino
LM2597/LM2597HV 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 12)
Use the following formula to select the appropriate resistor
values.
EXAMPLE (Adjustable Output Voltage Version)
Given:
VOUT = 20V
VIN(max) = 28V
ILOAD(max) = 0.5A
F = Switching Frequency (Fixed at a nominal 150 kHz).
1. Programming Output Voltage (Selecting R1 and R2, as
shown in Figure 12)
Select R1 to be 1 k, 1%. Solve for R2.
Select a value for R1 between 240and 1.5 k. The lower re-
sistor values minimize noise pickup in the sensitive feedback
pin. (For the lowest temperature coefficient and the best sta-
bility with time, use 1% metal film resistors.)
R2 = 1k (16.26 − 1) = 15.26k, closest 1% value is 15.4 k.
R2 = 15.4 k.
2. Inductor Selection (L1)
A. Calculate the inductor Volt microsecond constant E T
(V µs), from the following formula:
2. Inductor Selection (L1)
A. Calculate the inductor Volt microsecond constant (E T),
where VSAT = internal switch saturation voltage = 0.9V
and VD = diode forward voltage drop = 0.5V
B. Use the E T value from the previous formula and match
it with the E T number on the vertical axis of the Inductor
Value Selection Guide shown in Figure 6.
C. on the horizontal axis, select the maximum load current.
D. Identify the inductance region intersected by the E T
value and the Maximum Load Current value. Each region is
identified by an inductance value and an inductor code (LXX).
E. Select an appropriate inductor from the four manufacturer’s
part numbers listed in Figure 7.
B. E T = 35.2 (V µs)
C. ILOAD(max) = 0.5A
D. From the inductor value selection guide shown in Figure 6,
the inductance region intersected by the 35 (V µs) horizontal
line and the 0.5A vertical line is 150 µH, and the inductor code
is L19.
E. From the table in Figure 7, locate line L19, and select an in-
ductor part number from the list of manufacturers part num-
bers.
11 www.national.com

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