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PDF LM2698MM-ADJ Data sheet ( Hoja de datos )
| Número de pieza | LM2698MM-ADJ | |
| Descripción | SIMPLE SWITCHER 1.35A Boost Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM2698MM-ADJ (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
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October 2001
LM2698
SIMPLE SWITCHER® 1.35A Boost Regulator
General Description
The LM2698 is a general purpose PWM boost converter.
The 1.9A, 18V, 0.2ohm internal switch enables the LM2698
to provide efficient power conversion to outputs ranging from
2.2V to 17V. It can operate with input voltages as low as 2.2V
and as high as 12V. Current-mode architecture provides
superior line and load regulation and simple frequency com-
pensation over the device’s 2.2V to 12V input voltage range.
The LM2698 sets the standard in power density and is
capable of supplying 12V at 400mA from a 5V input. The
LM2698 can also be used in flyback or SEPIC topologies.
The LM2698 SIMPLE SWITCHER® features a pin selectable
switching frequency of either 600kHz or 1.25MHz. This pro-
motes flexibility in component selection and filtering tech-
niques. A shutdown pin is available to suspend the device
and decrease the quiescent current to 5µA. An external
compensation pin gives the user flexibility in setting fre-
quency compensation, which makes possible the use of
small, low ESR ceramic capacitors at the output. Switchers
Made Simple® software is available to insure a quick, easy
and guaranteed design. The LM2698 is available in a low
profile 8-lead MSOP package.
Features
n 1.9A, 0.2Ω, internal switch (typical)
n Operating voltage as low as 2.2V
n 600kHz/1.25MHz adjustable frequency operation
n Switchers Made Simple® software
n 8-Lead MSOP package
Applications
n 3.3V to 5V, 5V to 12V conversion
n Distributed Power
n Set-Top Boxes
n DSL Modems
n Diagnostic Medical Instrumentation
n Boost Converters
n Flyback Converters
n SEPIC Converters
Typical Application Circuit
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 2001 National Semiconductor Corporation DS200126
20012658
www.national.com
1 page  
Electrical Characteristics (Continued)
Specifications in standard type face are for TJ = 25˚C and those with boldface type apply over the full Operating Tempera-
ture Range ( TJ = −40˚C to +125˚C)Unless otherwise specified. VIN =2.2V and IL = 0A, unless otherwise specified.
Symbol
Parameter
Conditions
Min
(Note 6)
Typ
(Note 7)
Max
(Note 6)
Units
θJA Thermal Resistance
Junction to Ambient
(Note 10)
235 ˚C/W
Junction to Ambient
225
(Note 11)
Junction to Ambient
220
(Note 12)
Junction to Ambient
200
(Note 13)
Junction to Ambient
195
(Note 14)
Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to
be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Shutdown and voltage frequency select should not exceed VIN.
Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJA,
and the ambient temperature, TA. See the Electrical Characteristics table for the thermal resistance of various layouts. The maximum allowable power dissipation
at any ambient temperature is calculated using: PD (MAX) = (TJ(MAX) − TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die
temperature, and the regulator will go into thermal shutdown.
Note 4: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 5: ESD susceptibility using the human body model is 500V for VC.
Note 6: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% tested
or guaranteed through statistical analysis. 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 7: Typical numbers are at 25˚C and represent the most likely norm.
Note 8: This is the switch current limit at 0% duty cycle. The switch current limit will change as a function of duty cycle. See Typical performance Characteristics
section for ICL vs. VIN
Note 9: Bias current flows into FB pin.
Note 10: Junction to ambient thermal resistance (no external heat sink) for the MSO8 package with minimal trace widths (0.010 inches) from the pins to the circuit.
See ’Scenario ’A’’ in the Power Dissipation section.
Note 11: Junction to ambient thermal resistance for the MSO8 package with minimal trace widths (0.010 inches) from the pins to the circuit and approximately
0.0191 sq. in. of copper heat sinking. See ’Scenario ’B’’ in the Power Dissipation section.
Note 12: Junction to ambient thermal resistance for the MSO8 package with minimal trace widths (0.010 inches) from the pins to the circuit and approximately
0.0465 sq. in. of copper heat sinking. See ’Scenario ’C’’ in the Power Dissipation section.
Note 13: Junction to ambient thermal resistance for the MSO8 package with minimal trace widths (0.010 inches) from the pins to the circuit and approximately
0.2523 sq. in. of copper heat sinking. See ’Scenario ’D’’ in the Power Dissipation section.
Note 14: Junction to ambient thermal resistance for the MSO8 package with minimal trace widths (0.010 inches) from the pins to the circuit and approximately
0.0098 sq. in. of copper heat sinking on the top layer and 0.0760 sq. in. of copper heat sinking on the bottom layer, with three 0.020 in. vias connecting the planes.
See ’Scenario ’E’’ in the Power Dissipation section.
5 www.national.com
5 Page 
Operation (Continued)
The goal of the compensation network is to provide the best
static and dynamic performance while insuring stability over
line and load variations. The relationship of stability and
performance can be best analyzed by plotting the magnitude
and phase of the open loop frequency response in the form
of a bode plot. A typical bode plot of the LM2698 open loop
frequency response is shown in Figure 5.
20012657
FIGURE 5. Bode plot of the LM2698 Frequency Response using the Typical Application Circuit
Poles are marked with an ’X’, and zeros are marked with a
’O’. The bolded ’O’ labeled ’fRHP’ is a right-half plane zero.
Right half plane zeros act like normal zeros to the magnitude
(+20dB/decade slope influence) and like poles to the phase
(−90˚ shift). Three curves are shown. The powerstage curve
is the frequency response of the powerstage, which includes
the switch, diode, inductor, output capacitor, and load. The
compensator curve is the frequency response of the com-
pensator, which is the error amp combined with the compen-
sation network. T is the product of the powerstage and the
compensator and is the complete open loop frequency re-
sponse. The power stage response is fixed by line and load
constraints, while the compensator is set by the external
compensation network at pin 1. The compensator can be
designed in a few simple steps as follows.
Quick Compensator Design
Calculate:
where ROUT = 875kΩ
Choose CC1 = 4.7nF
Choose
where,
Where,
11 www.national.com
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| PDF Descargar | [ Datasheet LM2698MM-ADJ.PDF ] | |
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