|
|
PDF LM5000 Data sheet ( Hoja de datos )
| Número de pieza | LM5000 | |
| Descripción | High Voltage Switch Mode Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM5000 (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
|
No Preview Available !
July 2003
LM5000
High Voltage Switch Mode Regulator
General Description
The LM5000 is a monolithic integrated circuit specifically
designed and optimized for flyback, boost or forward power
converter applications. The internal power switch is rated for
a maximum of 80V, with a current limit set to 2A. Protecting
the power switch are current limit and thermal shutdown
circuits. The current mode control scheme provides excellent
rejection of line transients and cycle-by-cycle current limiting.
An external compensation pin and the built-in slope compen-
sation allow the user to optimize the frequency compensa-
tion. Other distinctive features include softstart to reduce
stresses during start-up and an external shutdown pin for
remote ON/OFF control. There are two operating frequency
ranges available. The LM5000-3 is pin selectable for either
300kHz (FS Grounded) or 700kHz (FS Open). The
LM5000-6 is pin selectable for either 600kHz (FS Grounded)
or 1.25MHz (FS Open). The device is available in a low
profile 16-lead TSSOP package (available now) or a ther-
mally enhanced 16-lead LLP package (coming in Q3CY03).
Features
n 80V internal switch
n Operating input voltage range of 3.1V to 40V
n Pin selectable operating frequency
300kHz/700kHz (-3)
600kHz/1.25MHz (-6)
n Adjustable output voltage
n External compensation
n Input undervoltage lockout
n Softstart
n Current limit
n Over temperature protection
n External shutdown
n Small 16-Lead TSSOP or 16-Lead LLP package
Applications
n Flyback Regulator
n Forward Regulator
n Boost Regulator
n DSL Modems
n Distributed Power Converters
Typical Application Circuit
LM5000 Flyback Converter
20031901
© 2003 National Semiconductor Corporation DS200319
www.national.com
1 page  
Typical Performance Characteristics
Iq (non-switching) vs VIN @ fSW = 300kHz
Iq (non-switching) vs VIN @ fSW = 700kHz
20031920
Iq (switching) vs VIN @ fSW = 300kHz
20031921
Iq (switching) vs VIN @ fSW = 700kHz
Vfb vs Temperature
20031922
RDS(ON) vs VIN @ ISW =1A
20031923
20031924
5
20031925
www.national.com
5 Page 
Operation (Continued)
The LM5000 is a current mode PWM regulator. The signal
flow of this control scheme has two feedback loops, one that
senses switch current and one that senses output voltage.
To keep a current programmed control converter stable
above duty cycles of 50%, the inductor must meet certain
criteria. The inductor, along with input and output voltage,
will determine the slope of the current through the inductor
(see Figure 4 (a)). If the slope of the inductor current is too
great, the circuit will be unstable above duty cycles of 50%.
The LM5000 provides a compensation pin (COMP) to cus-
tomize the voltage loop feedback. It is recommended that a
series combination of RC and CC be used for the compen-
sation network, as shown in Figure 1. The series combina-
tion of RC and CC introduces pole-zero pair according to the
following equations:
where RO is the output impedance of the error amplifier,
850kΩ. For most applications, performance can be opti-
mized by choosing values within the range 5kΩ ≤ RC ≤ 20kΩ
and 680pF ≤ CC ≤ 4.7nF.
COMPENSATION
This section will present a general design procedure to help
insure a stable and operational circuit. The designs in this
datasheet are optimized for particular requirements. If differ-
ent conversions are required, some of the components may
need to be changed to ensure stability. Below is a set of
general guidelines in designing a stable circuit for continu-
ous conduction operation (loads greater than 100mA), in
most all cases this will provide for stability during discontinu-
ous operation as well. The power components and their
effects will be determined first, then the compensation com-
ponents will be chosen to produce stability.
INDUCTOR SELECTION
To ensure stability at duty cycles above 50%, the inductor
must have some minimum value determined by the mini-
mum input voltage and the maximum output voltage. This
equation is:
where fs is the switching frequency, D is the duty cycle, and
RDSON is the ON resistance of the internal switch. This
equation is only good for duty cycles greater than 50%
(D>0.5).
The inductor ripple current is important for a few reasons.
One reason is because the peak switch current will be the
average inductor current (input current) plus ∆iL. Care must
be taken to make sure that the switch will not reach its
current limit during normal operation. The inductor must also
be sized accordingly. It should have a saturation current
rating higher than the peak inductor current expected. The
output voltage ripple is also affected by the total ripple cur-
rent.
DC GAIN AND OPEN-LOOP GAIN
Since the control stage of the converter forms a complete
feedback loop with the power components, it forms a closed-
loop system that must be stabilized to avoid positive feed-
back and instability. A value for open-loop DC gain will be
required, from which you can calculate, or place, poles and
zeros to determine the crossover frequency and the phase
margin. A high phase margin (greater than 45˚) is desired for
the best stability and transient response. For the purpose of
stabilizing the LM5000, choosing a crossover point well be-
low where the right half plane zero is located will ensure
sufficient phase margin. A discussion of the right half plane
zero and checking the crossover using the DC gain will
follow.
OUTPUT CAPACITOR SELECTION
The choice of output capacitors is somewhat more arbitrary.
It is recommended that low ESR (Equivalent Series Resis-
tance, denoted RESR) capacitors be used such as ceramic,
polymer electrolytic, or low ESR tantalum. Higher ESR ca-
pacitors may be used but will require more compensation
which will be explained later on in the section. The ESR is
also important because it determines the output voltage
ripple according to the approximate equation:
∆VOUT ) 2∆iLRESR (in Volts)
After choosing the output capacitor you can determine a
pole-zero pair introduced into the control loop by the follow-
ing equations:
Where RL is the minimum load resistance corresponding to
the maximum load current. The zero created by the ESR of
the output capacitor is generally very high frequency if the
ESR is small. If low ESR capacitors are used it can be
neglected. If higher ESR capacitors are used see the High
Output Capacitor ESR Compensation section.
RIGHT HALF PLANE ZERO
A current mode control boost regulator has an inherent right
half plane zero (RHP zero). This zero has the effect of a zero
in the gain plot, causing an imposed +20dB/decade on the
rolloff, but has the effect of a pole in the phase, subtracting
another 90˚ in the phase plot. This can cause undesirable
effects if the control loop is influenced by this zero. To ensure
the RHP zero does not cause instability issues, the control
loop should be designed to have a bandwidth of 1⁄2 the
frequency of the RHP zero or less. This zero occurs at a
frequency of:
11 www.national.com
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet LM5000.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM5000 | High Voltage Switch Mode Regulator | National Semiconductor |
| LM5000 | LM5000 High Voltage Switch Mode Regulator (Rev. D) |  Texas Instruments |
| LM5000EP | LM5000EP Enhanced Plastic High Voltage Switch Mode Regulator (Rev. B) | Texas Instruments |
| LM5000EP | Enhanced Plastic High Voltage Switch Mode Regulator | National Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |