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LM3524 Datasheet

Download or read online National Semiconductor LM3524 Regulating Pulse Width Modulator pdf datasheet.

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Regulating Pulse Width Modulator
General Description
The LM3524D family is an improved version of the industry
standard LM3524. It has improved specifications and addi-
tional features yet is pin for pin compatible with existing 3524
families. New features reduce the need for additional exter-
nal circuitry often required in the original version.
The LM3524D has a
1% precision 5V reference. The cur-
rent carrying capability of the output drive transistors has
been raised to 200 mA while reducing V
breakdown to 60V. The common mode voltage range of
the error-amp has been raised to 5.5V to eliminate the need
for a resistive divider from the 5V reference.
In the LM3524D the circuit bias line has been isolated from
the shut-down pin. This prevents the oscillator pulse ampli-
tude and frequency from being disturbed by shut-down. Also
at high frequencies ( 300 kHz) the max. duty cycle per out-
put has been improved to 44% compared to 35% max. duty
cycle in other 3524s.
In addition, the LM3524D can now be synchronized exter-
nally, through pin 3. Also a latch has been added to insure
Block Diagram
© 1999 National Semiconductor Corporation
one pulse per period even in noisy environments. The
LM3524D includes double pulse suppression logic that in-
sures when a shut-down condition is removed the state of
the T-flip-flop will change only after the first clock pulse has
arrived. This feature prevents the same output from being
pulsed twice in a row, thus reducing the possibility of core
saturation in push-pull designs.
and increasing
n Fully interchangeable with standard LM3524 family
1% precision 5V reference with thermal shut-down
n Output current to 200 mA DC
n 60V output capability
n Wide common mode input range for error-amp
n One pulse per period (noise suppression)
n Improved max. duty cycle at high frequencies
n Double pulse suppression
n Synchronize through pin 3
June 1999

Summary of Contents

Page 1

... In the LM3524D the circuit bias line has been isolated from the shut-down pin. This prevents the oscillator pulse ampli- tude and frequency from being disturbed by shut-down. Also at high frequencies ( 300 kHz) the max ...

Page 2

... T 0.01 µF 3.4 3.6 3 0.01 µF 1.1 0.8 0 40C to 125C 0C to 125C 150 65C to 150C 260C LM3524D Tested Design Units Typ Limit Limit (Note 3) (Note 4) 5 4.75 V Min 5.25 V Max Max Max 66 dB ...

Page 3

... 0.01 µ 0.001 µ 3.5 1 180 (Pin 1) 200 220 0.2 0 0.5 (Pin 1) 1 LM3524D Tested Design Units Typ Limit Limit (Note 3) (Note 4) 0.5 1 µA Max 65 µA Min 95 125 µA Max 125 µA Min 95 65 µA Max ...

Page 4

... IN IN Note 1: Unless otherwise stated, these specifications apply for T 20V and f and LM3524D is 0C to 70 OSC Note 2: For operation at elevated temperatures, devices in the N package must be derated based on a thermal resistance of 86C/W, junction to ambient. Devices in the M package must be derated at 125C/W, junction to ambient. ...

Page 5

Typical Performance Characteristics Output Transistor Saturation Voltage DS008650-31 Standby Current vs Voltage DS008650-34 Test Circuit (Continued) Output Transistor Emitter Voltage DS008650-32 Standby Current vs Temperature DS008650-35 5 Reference Transistor Peak Output Current DS008650-33 Current Limit Sense Voltage DS008650-36 DS008650-4 ...

Page 6

... Functional Description INTERNAL VOLTAGE REGULATOR The LM3524D has an on-chip 5V, 50 mA, short circuit pro- tected voltage regulator. This voltage regulator provides a supply for all internal circuitry of the device and can be used as an external reference. For input voltages of less than 8V the 5V output should be shorted to pin 15 which disables the 5V regulator ...

Page 7

... OUTPUT STAGES The outputs of the LM3524D are NPN transistors, capable of a maximum current of 200 mA. These transistors are driven 180 out of phase and have non-committed open collectors and emitters as shown in Figure 6 . ...

Page 8

Typical Applications FIGURE 7. Positive Regulator, Step-Up Basic Configuration (I FIGURE 8. Positive Regulator, Step-Up Boosted Current Configuration DS008650- mA) IN(MAX) DS008650-12 8 ...

Page 9

Typical Applications (Continued) FIGURE 9. Positive Regulator, Step-Down Basic Configuration (I FIGURE 10. Positive Regulator, Step-Down Boosted Current Configuration DS008650- mA) IN(MAX) DS008650-14 9 ...

Page 10

... BASIC SWITCHING REGULATOR THEORY AND APPLICATIONS The basic circuit of a step-down switching regulator circuit is shown in Figure 12 , along with a practical circuit design us- ing the LM3524D in Figure 15 . FIGURE 12. Basic Step-Down Switching Regulator The circuit works as follows used as a switch, which has ON and OFF times controlled by the pulse width modu- lator. When Q1 is ON, power is drawn from V to the load through L1 ...

Page 11

Typical Applications (Continued) FIGURE 13. Relation of Switch Timing to Inductor Current in Step-Down Regulator I Neglecting and settling I SAT where T Total Period The above shows the relation ...

Page 12

... A complete step-down switching regulator schematic, using the LM3524D, is illustrated in Figure 15 . Transistors Q1 and Q2 have been added to boost the output to 1A. The 5V regu- lator of the LM3524D has been divided in half to bias the er- ror amplifiers non-inverting input to within its common-mode Mounted to Staver Heatsink No. V5-1. ...

Page 13

Typical Applications (Continued) Parameter Output Voltage Switching Frequency Short Circuit Current Limit Load Regulation Line Regulation Efficiency Output Ripple FIGURE 16. 5V, 1 Amp Switching Regulator, Foil Side FIGURE 17. Stuffing Diagram, Component Side TABLE 1. Conditions Typical Characteristics ...

Page 14

Typical Applications (Continued) THE STEP-UP SWITCHING REGULATOR Figure 18 shows the basic circuit for a step-up switching regulator. In this circuit Q1 is used as a switch to alternately apply V across inductor L1. During the time and ...

Page 15

... It should also be noted that this circuit has no sup- ply rejection. By adding a reference voltage at the non-inverting input to the error amplifier, see Figure 21 , the input voltage variations are rejected. The LM3524D can also be used in inductorless switching regulators. Figure 22 shows a polarity inverter which if con- nected to Figure 20 provides a 15V unregulated output. 15 ...

Page 16

Typical Applications (Continued) > turns No. 24 wire on Ferroxcube No. K300502 Toroid core. FIGURE 20. 15V, 0.5A Step-Up Switching Regulator DS008650-26 FIGURE 21. Replacing R3/R4 Divider in Figure 20 with Reference Circuit Improves Line Regulation ...

Page 17

... Connection Diagram Order Number LM2524DN or LM3524DN DS008650-2 Top View See NS Package Number N16E Order Number LM3524DM See NS Package Number M16A 17 ...

Page 18

... Physical Dimensions inches (millimeters) unless otherwise noted Molded Surface-Mount Package (M) Order Number LM3524DM NS Package Number M16A 18 ...

Page 19

... National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. Molded Dual-In-Line Package (N) Order Number LM2524DN or LM3524DN NS Package Number N16E 2 ...

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