NSC LM2598T-5.0, LM2598T-3.3, LM2598SX-ADJ, LM2598SX-5.0, LM2598SX-3.3 Datasheet

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 available in fixed output voltages of 3.3V, 5V, 12V, and an adjustable 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 compensation², 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 50ÊC, no heat sink is required.

A standard series of inductors (both through hole and surface mount types) are available from several different manufacturers optimized for use with the LM2598 series. This feature greatly simplifies the design of switch-mode power supplies.

Other features include a guaranteed ±4% tolerance on output 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

n3.3V, 5V, 12V, and adjustable output versions

nAdjustable version output voltage range, 1.2V to 37V

±4% max over line and load conditions

nGuaranteed 1A output current

nAvailable in 7-pin TO-220 and TO-263 (surface mount) package

nInput voltage range up to 40V

nExcellent line and load regulation specifications

n150 kHz fixed frequency internal oscillator

nShutdown /Soft-start

nOut of regulation error flag

nError output delay

nLow power standby mode, IQ typically 85 µA

nHigh Efficiency

nUses readily available standard inductors

nThermal shutdown and current limit protection

Applications

nSimple high-efficiency step-down (buck) regulator

nEfficient pre-regulator for linear regulators

nOn-card switching regulators

nPositive to Negative converter

Typical Application (Fixed Output Voltage Versions)

DS012593-1

²Patent Number 5,382,918.

SIMPLE SWITCHER® and Switchers Made Simple® are registered trademarks of National Semiconductor Corporation.

with Regulator, Voltage Down-Step 1A kHz 150 Converter Power SWITCHER SIMPLE LM2598

Features

© 1999 National Semiconductor Corporation

DS012593

www.national.com

Connection Diagrams and Order Information

Bent and Staggered Leads, Through Hole Package

7-Lead TO-220 (T)

Surface Mount Package

7-Lead TO-263 (S)

		DS012593-22
	DS012593-50	Order Number LM2598S-3.3, LM2598S-5.0,
	Order Number LM2598T-3.3, LM2598T-5.0,
		LM2598S-12 or LM2598S-ADJ
	LM2598T-12 or LM2598T-ADJ
		See NS Package Number TS7B
	See NS Package Number TA07B

www.national.com

2

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Maximum Supply Voltage (VIN)			45V
			6V
SD/SS Pin Input Voltage (Note 2)
Delay Pin Voltage (Note 2)			1.5V
Flag Pin Voltage		−0.3	≤ V ≤ +45V
Feedback Pin Voltage		−0.3	≤ V ≤ +25V
Output Voltage to Ground
(Steady State)			−1V
Power Dissipation		Internally limited
Storage Temperature Range		−65ÊC to +150ÊC

ESD Susceptibility
Human Body Model (Note 3)	2 kV
Lead Temperature
S Package
Vapor Phase (60 sec.)	+215ÊC
Infrared (10 sec.)	+245ÊC
T Package (Soldering, 10 sec.)	+260ÊC
Maximum Junction Temperature	+150ÊC

Operating Conditions

Temperature Range	−25ÊC ≤ TJ ≤ +125ÊC
Supply Voltage	4.5V to 40V

LM2598-3.3

Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range.

Symbol	Parameter	Conditions	LM2598-3.3		Units
					(Limits)
			Typ	Limit
			(Note 4)	(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VOUT	Output Voltage	4.75V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A	3.3		V
				3.168/3.135	V(min)
				3.432/3.465	V(max)
η	Efficiency	VIN = 12V, ILOAD = 1A	78		%

LM2598-5.0

Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range.

Symbol	Parameter	Conditions		LM2598-5.0		Units
						(Limits)
			Typ		Limit
			(Note 4)		(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VOUT	Output Voltage	7V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A	5			V
					4.800/4.750	V(min)
					5.200/5.250	V(max)
η	Efficiency	VIN = 12V, ILOAD = 1A	82			%

LM2598-12

Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range.

Symbol	Parameter	Conditions		LM2598-12		Units
						(Limits)
			Typ		Limit
			(Note 4)		(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VOUT	Output Voltage	15V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A	12			V
					11.52/11.40	V(min)
					12.48/12.60	V(max)
η	Efficiency	VIN = 25V, ILOAD = 1A	90			%

3	www.national.com

LM2598-ADJ

Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range.

Symbol	Parameter	Conditions	LM2598-ADJ		Units
					(Limits)
			Typ	Limit
			(Note 4)	(Note 5)
SYSTEM PARAMETERS (Note 6) Test Circuit Figure 1
VFB	Feedback Voltage	4.5V ≤ VIN ≤ 40V, 0.1A ≤ ILOAD ≤ 1A	1.230		V
		VOUT programmed for 3V. Circuit of Figure 12.		1.193/1.180	V(min)
				1.267/1.280	V(max)
η	Efficiency	VIN = 12V, VOUT = 3V, ILOAD = 1A	78		%

All Output Voltage Versions Electrical Characteristics

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD = 200 mA

Symbol	Parameter			Conditions	LM2598-XX		Units
							(Limits)
					Typ	Limit
					(Note 4)	(Note 5)
DEVICE PARAMETERS
Ib	Feedback Bias Current		Adjustable Version Only, VFB = 1.3V		10		nA
						50/100	nA(max)
fO	Oscillator Frequency		(Note 7)		150		kHz
						127/110	kHz(min)
						173/173	kHz(max)
VSAT	Saturation Voltage		IOUT = 1A (Note 8) (Note 9)		1		V
						1.2/1.3	V(max)
DC	Max Duty Cycle (ON)	(Note 9)			100		%
	Min Duty Cycle (OFF)	(Note 10)			0
ICL	Current Limit		Peak Current, (Note 8) (Note 9)		1.5		A
						1.2/1.15	A(min)
						2.4/2.6	A(max)
IL	Output Leakage Current		Output = 0V (Note 9) (Note 10) (Note 11)			50	µA(max)
			Output = −1V		2		mA
						15	mA(max)
IQ	Operating Quiescent				5		mA
			SD	/SS Pin Open, (Note 10)
	Current					10	mA(max)
ISTBY	Standby Quiescent			/SS pin = 0V, (Note 11)	85		µA
			SD
	Current					200/250	µA(max)
θJC	Thermal Resistance		TO220 or TO263 Package, Junction to Case		2		ÊC/W
θJA			TO220 Package, Junction to Ambient (Note 12)		50		ÊC/W
θJA			TO263 Package, Junction to Ambient (Note 13)		50		ÊC/W
θJA			TO263 Package, Junction to Ambient (Note 14)		30		ÊC/W
θJA			TO263 Package, Junction to Ambient (Note 15)		20		ÊC/W
SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure 1
VSD	Shutdown Threshold				1.3		V
	Voltage		Low, (Shutdown Mode)			0.6	V(max)
			High, (Soft-start Mode)			2	V(min)
VSS	Soft-start Voltage		VOUT = 20% of Nominal Output Voltage		2		V
			VOUT = 100% of Nominal Output Voltage		3

www.national.com

4

All Output Voltage Versions

Electrical Characteristics (Continued)

Specifications with standard type face are for TJ = 25ÊC, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable version and VIN = 24V for the 12V version. ILOAD = 200 mA

Symbol	Parameter			Conditions	LM2598-XX		Units
							(Limits)
					Typ	Limit
					(Note 4)	(Note 5)
SHUTDOWN/SOFT-START CONTROL Test Circuit of Figure 1
ISD	Shutdown Current	V	SHUTDOWN	= 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	Flag Output Saturation	ISINK = 3 mA			0.3		V
	Voltage	VDELAY = 0.5V				0.7/1.0	V(max)
IFL	Flag Output Leakage	VFLAG = 40V			0.3		µA
	Current
	Delay Pin Threshold				1.25		V
	Voltage	Low (Flag ON)				1.21	V(min)
		High (Flag OFF) and VOUT Regulated				1.29	V(max)
	Delay Pin Source Current	VDELAY = 0.5V			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 intended 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 25ÊC 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% production 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 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 overload.

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

Typical Performance Characteristics (Circuit of Figure 1)

Normalized	Line Regulation	Efficiency
Output Voltage

	DS012593-3	DS012593-14
	DS012593-2
Switch Saturation	Switch Current Limit	Dropout Voltage
Voltage

	DS012593-16	DS012593-17
	DS012593-15
Operating	Shutdown	Minimum Operating
Quiescent Current	Quiescent Current	Supply Voltage

DS012593-4 DS012593-5 DS012593-6

Feedback Pin	Flag Saturation	Switching Frequency
Bias Current	Voltage

DS012593-8

DS012593-49

DS012593-7

www.national.com

6

Typical Performance Characteristics (Circuit of Figure 1) (Continued)

Soft-start	Shutdown/Soft-start	Delay Pin Current
	Current

	DS012593-9		DS012593-11
		DS012593-10
Soft-start Response		Shutdown/Soft-start
		Threshold Voltage

DS012593-12

	DS012593-13
Typical Performance Characteristics (Circuit of Figure 1)
Continuous Mode Switching Waveforms	Discontinuous Mode Switching Waveforms
VIN = 20V, VOUT = 5V, ILOAD = 1A
L = 68 µH, C OUT = 120 µF, C OUT ESR = 100 mΩ	VIN = 20V, VOUT = 5V, ILOAD = 600 mA
	L = 22 µH, C OUT = 220 µF, C OUT ESR = 50 mΩ

		DS012593-18
	A: Output Pin Voltage, 10V/div.	DS012593-19
		A: Output Pin Voltage, 10V/div.
	B: Inductor Current 0.5A/div.
		B: Inductor Current 0.5A/div.
	C: Output Ripple Voltage, 50 mV/div.
		C: Output Ripple Voltage, 50 mV/div.

Horizontal Time Base: 2 µs/div.

Horizontal Time Base: 2 µs/div.

7	www.national.com

Typical Performance Characteristics

Load Transient Response for Continuous Mode

VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 750 mA L = 68 µH, C OUT = 120 µF, C OUT ESR = 100 mΩ

(Circuit of Figure 1) (Continued)

Load Transient Response for Discontinuous Mode

VIN = 20V, VOUT = 5V, ILOAD = 250 mA to 750 mA L = 22 µH, C OUT = 220 µF, C OUT ESR = 50 mΩ

		DS012593-20
	A: Output Voltage, 100 mV/div. (AC)	DS012593-21
		A: Output Voltage, 100 mV/div. (AC)
	B: 250 mA to 750 mA Load Pulse
		B: 250 mA to 750 mA Load Pulse
	Horizontal Time Base: 100 µs/div.
		Horizontal Time Base: 200 µs/div.

www.national.com

8

Test Circuit and Layout Guidelines

Fixed Output Voltage Versions

DS012593-23

Component Values shown are for VIN = 15V, VOUT = 5V, ILOAD = 1A. 120 µF, 50V, Aluminum Electrolytic Nichicon ªPL Seriesº

120 µF, 35V Aluminum Electrolytic, Nichicon ªPL Seriesº 3A, 40V Schottky Rectifier, 1N5822

68 µH, L30

Typical Values

*CSS: Ð 0.1 µF

CDELAY: Ð 0.1 µF

RPull Up: Ð 4.7k

Adjustable Output Voltage Versions

DS012593-24

where VREF = 1.23V

Select R1 to be approximately 1kΩ, use a 1% resistor for best stability.

Component Values shown are for VIN = 20V,

VOUT = 10V, ILOAD = 1A.

CIN	Ð	120 µF, 35V, Aluminum Electrolytic Nichicon ªPL Seriesº
COUT		Ð	120 µF, 35V Aluminum Electrolytic, Nichicon ªPL Seriesº
D1 Ð 3A,			40V Schottky Rectifier, 1N5822
L1	Ð 100		µH, L29
R1	Ð 1 k Ω, 1%
R2	Ð 7.15k, 1 %
CFF	Ð 3.3 nF, See Application Information Section
RFF	Ð 3 k Ω, See Application Information Section

Typical Values

CSS Ð 0.1 µF

CDELAY Ð 0.1 µF

RPULL UP Ð 4.7k

FIGURE 1. Standard Test Circuits and Layout Guides

9	www.national.com

Test Circuit and Layout Guidelines

(Continued)

As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines should be wide printed circuit traces and should be kept as short as possible. For best results, external components should be located as close to the switcher lC as possible using ground plane construction or single point grounding.

If open core inductors are used, special care must be taken as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, lC groundpath and COUT wiring can cause problems.

When using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. (See application section for more information.)

LM2598 Series Buck Regulator Design Procedure (Fixed Output)

PROCEDURE (Fixed Output Voltage Version)	EXAMPLE (Fixed Output Voltage Version)
Given:	Given:
VOUT = Regulated Output Voltage (3.3V, 5V or 12V)	VOUT = 5V
VIN(max) = Maximum DC Input Voltage	VIN(max) = 12V
ILOAD(max) = Maximum Load Current	ILOAD(max) = 1A
1. Inductor Selection (L1)	1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Fig-	A. Use the inductor selection guide for the 5V version shown
ures Figure 4, Figure 5, or Figure 6 (Output voltages of 3.3V,	in Figure 5.
5V, or 12V respectively.) For all other voltages, see the de-
sign procedure for the adjustable version.
B. From the inductor value selection guide, identify the induc-	B. From the inductor value selection guide shown in Figure 5,
tance region intersected by the Maximum Input Voltage line	the inductance region intersected by the 12V horizontal line
and the Maximum Load Current line. Each region is identified	and the 1A vertical line is 68 µH, and the inductor code is
by an inductance value and an inductor code (LXX).	L30.
C. Select an appropriate inductor from the four manufactur-	C. The inductance value required is 68 µH. From the table in
er's part numbers listed in Figure 8.	Figure 8, go to the L30 line and choose an inductor part num-
	ber from any of the four manufacturers shown. (In most in-
	stance, both through hole and surface mount inductors are
	available.)
2. Output Capacitor Selection (COUT)	2. Output Capacitor Selection (COUT)
A. In the majority of applications, low ESR (Equivalent Series	A. See section on output capacitors in application infor-
Resistance) electrolytic capacitors between 47 µF and 330	mation section.
µF and low ESR solid tantalum capacitors between 56 µF
and 270 µF provide the best results. This capacitor should be
located close to the IC using short capacitor leads and short
copper traces. Do not use capacitors larger than 330 µF.
For additional information, see section on output capaci-
tors in application information section.

www.national.com

10