|
|
PDF LM22680 Data sheet ( Hoja de datos )
| Número de pieza | LM22680 | |
| Descripción | Step-Down Voltage Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LM22680 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
December 12, 2008
LM22680
2A SIMPLE SWITCHER®, Step-Down Voltage Regulator
www.dawtasihteeht4u.Fcoem atures
General Description
The LM22680 series of regulators are monolithic integrated
circuits which provide all of the active functions for a step-
down (buck) switching regulator capable of driving up to 2A
loads with excellent line and load regulation characteristics.
High efficiency (>90%) is obtained through the use of a low
ON-resistance N-channel MOSFET.
The SIMPLE SWITCHER® concept provides for an easy to
use complete design using a minimum number of external
components and National’s WEBENCH® design tool.
National’s WEBENCH® tool includes features such as exter-
nal component calculation, electrical simulation, thermal sim-
ulation, and Build-It boards for easy design-in. The switching
clock frequency is provided by an internal fixed frequency os-
cillator which operates at 500 kHz. The switching frequency
can also be adjusted with an external resistor or synchronized
to an external clock up to 1MHz. It is also possible to self-
synchronize multiple regulators to share the same switching
frequency. The LM22680 series also has built in thermal shut-
down, current limiting and an enable control input that can
power down the regulator to a low 25 µA quiescent current
standby condition. An adjustable soft-start feature is provided
by selecting an appropriate external soft-start capacitor.
Features
■ Wide input voltage range: 4.5V to 42V
■ Internally compensated voltage mode control
■ Stable with low ESR ceramic capacitors
■ 200 mΩ N-channel MOSFET
■ Output voltage option:
-ADJ (outputs as low as 1.285V)
■ ±1.5% feedback reference accuracy
■ Switching frequency of 500 kHz, adjustable between
200 kHz and 1 MHz
■ -40°C to 125°C operating junction temperature range
■ Precision enable pin
■ Integrated boot diode
■ Adjustable soft-start
■ Fully WEBENCH® enabled
■ Step-down and inverting buck-boost applications
Package
■ PSOP-8 (Exposed Pad)
Applications
■ Industrial Control
■ Telecom and Datacom Systems
■ Embedded Systems
■ Automotive Telematics and Body Electronics
■ Conversions from Standard 24V, 12V and 5V Input Rails
Simplified Application Schematic
© 2008 National Semiconductor Corporation 300807
30080701
www.national.com
1 page  
Feedback Bias Current vs Temperature
Normalized Enable Threshold Voltage vs Temperature
www.datasheet4u.com
30080705
Standby Quiescent Current vs Input Voltage
30080710
Normalized Feedback Voltage vs Temperature
30080706
Normalized Feedback Voltage vs Input Voltage
30080707
Switching Frequency vs RT/SYNC Resistor
30080709
5
30080713
www.national.com
5 Page 
excessive voltages during a line transient and will also move
the resonance frequency of the input filter away from the reg-
ulator bandwidth.
Output Capacitor
The output capacitor can limit the output ripple voltage and
provide a source of charge for transient loading conditions.
Multiple capacitors can be placed in parallel. Very low ESR
capacitors such as ceramic capacitors reduce the output rip-
wwpitowler.sdvaointlataspghaeeraealtnl4edul .npcooroimsveidsepilkaergse, wbhuillke
larger higher
capacitance
ESR capac-
for transient
loading conditions. An approximation for the output voltage
ripple is:
where ΔIL is the inductor ripple current.
If the switching frequency is set higher than 500 kHz, the ca-
pacitance value may not be reduced accordingly due to sta-
bility requirements. The internal compensation is optimized
for circuits with a 500 kHz switching frequency. See the in-
ternal compensation section for more details.
Cboot Capacitor
The bootstrap capacitor between the BOOT pin and the SW
pin supplies the gate current to turn on the N-channel MOS-
FET. The recommended value of this capacitor is 10 nF and
should be a good quality, low ESR ceramic capacitor.
It is possible to put a small resistor in series with the Cboot
capacitor to slow down the turn-on transition time of the in-
ternal N-channel MOSFET. Resistors in the range of 10Ω to
50Ω can slow down the transition time. This can reduce EMI
of a switched mode power supply circuit. Using such a series
resistor is not recommended for every design since it will in-
crease the switching losses of the application and makes
thermal considerations more challenging.
Resistor Divider
For the LM22680 no resistor divider is required for 1.285V
output voltage. The output voltage should be directly con-
nected to the FB pin. Other output voltages can use a resistor
divider.
The resistor values can be determined by the following equa-
tions:
-5.0 option:
Where VFB = 1.285V typical.
30080723
FIGURE 4. Resistive Feedback Divider
A maximum value of 10 kΩ is recommended for the sum of
R1 and R2 to keep high output voltage accuracy.
At loads less than 5 mA, the boot capacitor will not hold
enough charge to power the internal high side driver. The
output voltage may droop until the boot capacitor is
recharged. Selecting a total feedback resistance to be below
3 kΩ will provide some minimal load and can keep the output
voltage from collapsing in such low load conditions.
Catch Diode
A Schottky type re-circulating diode is required for all
LM22680 applications. Ultra-fast diodes which are not Schot-
tky diodes are not recommended and may result in damage
to the IC due to reverse recovery current transients. The near
ideal reverse recovery characteristics and low forward volt-
age drop of Schottky diodes are particularly important diode
characteristics for high input voltage and low output voltage
applications common to the LM22680. The reverse recovery
characteristic determines how long the current surge lasts
each cycle when the N-channel MOSFET is turned on. The
reverse recovery characteristics of Schottky diodes mini-
mizes the peak instantaneous power in the switch occurring
during turn-on for each cycle. The resulting switching losses
are significantly reduced when using a Schottky diode. The
reverse breakdown rating should be selected for the maxi-
mum VIN, plus some safety margin. A rule of thumb is to select
a diode with the reverse voltage rating of 1.3 times the max-
imum input voltage.
The forward voltage drop has a significant impact on the con-
version efficiency, especially for applications with a low output
voltage. ‘Rated’ current for diodes varies widely from various
manufacturers. The worst case is to assume a short circuit
load condition. In this case the diode will carry the output cur-
rent almost continuously. For the LM22680 this current can
be as high as 2.8A (typical). Assuming a worst case 1V drop
across the diode, the maximum diode power dissipation can
be as high as 2.8W.
Circuit Board Layout
Board layout is critical for switching power supplies. First, the
ground plane area must be sufficient for thermal dissipation
purposes. Second, appropriate guidelines must be followed
to reduce the effects of switching noise. Switch mode con-
verters are very fast switching devices. In such devices, the
rapid increase of input current combined with the parasitic
trace inductance generates unwanted L di/dt noise spikes.
The magnitude of this noise tends to increase as the output
current increases. This parasitic spike noise may turn into
electromagnetic interference (EMI) and can also cause prob-
lems in device performance. Therefore, care must be taken
in layout to minimize the effect of this switching noise.
11 www.national.com
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LM22680.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LM22680 | LM22680/-Q1 42 V 2 A SIMPLE SWITCHER Step-Down Voltage Regulator With Features (Rev. L) |  Texas Instruments |
| LM22680 | Step-Down Voltage Regulator | National Semiconductor |
| LM22680-Q1 | LM22680/-Q1 42 V 2 A SIMPLE SWITCHER Step-Down Voltage Regulator With Features (Rev. L) | Texas Instruments |
| 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 |