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PDF RT8268 Data sheet ( Hoja de datos )
| Número de pieza | RT8268 | |
| Descripción | 400kHz Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT8268 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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RT8268
2A, 24V, 400kHz Step-Down Converter
General Description
The RT8268 is a high voltage buck converter that can
support the input voltage range from 4.75V to 24V and the
output current can be up to 2A. Current Mode operation
provides fast transient response and eases loop
stabilization. The RT8268 also provides adjustable soft-
start to be a flexible solution for customers.
The chip provides protection functions such as cycle-by-
cycle current limiting and thermal shutdown protection.
In shutdown mode, the regulator draws 22μA of supply
current. The RT8268 is available in the SOP-8 and
MSOP-10 (Exposed Pad) surface mount package.
Ordering Information
RT8268
Package Type
S : SOP-8
FP : MSOP-10 (Exposed Pad)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Features
z Wide Operating Input Range : 4.75V to 24V
z Adjustable Output Voltage Range : 0.92V to 16V
z Output Current up to 2A
z 22μA Low Shutdown Current
z Power MOSFET : 0.18Ω
z High Efficiency up to 95%
z 400kHz Fixed Switching Frequency
z Stable with Low ESR Output Ceramic Capacitors
z Programmable Soft-Start
z Thermal Shutdown Protection
z Cycle-By-Cycle Over Current Protection
z RoHS Compliant and Halogen Free
Applications
z Distributive Power Systems
z Battery Charger
z DSL Modems
z Pre-regulator for Linear Regulators
http://www.DataSheet4U.net/
Pin Configurations
(TOP VIEW)
NC
BOOT
NC
VIN
SW
10
29
3 GND 8
4 11 7
56
SS
EN
COMP
FB
GND
MSOP-10 (Exposed Pad)
BOOT
VIN
SW
GND
8
27
36
45
SOP-8
SS
EN
COMP
FB
DS8268-02 March 2011
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8268
Parameter
En input Low Voltage
En input High Voltage
Enable Pull-up Current
Shutdown Current
Quiescent Current
Soft-Start Period
Thermal Shutdown
Symbol
Test Conditions
ISHDN
IQ
TSD
VEN = 0V
VEN = 0V
VEN = 2V, VFB = 1V
CSS = 10nF
Min Typ Max Unit
-- -- 0.4 V
1.4 -- 5.5 V
-- 1 -- μA
-- 22 36 μA
-- 0.6 1 mA
-- 1 -- ms
-- 150 -- °C
Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in the natural convection at TA = 25°C on a high effective thermal conductivity four layers test board of
JEDEC 51-7 thermal measurement standard. The case point of θJC is on the expose pad for MSOP-10 (Exposed Pad)
package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
http://www.DataSheet4U.net/
DS8268-02 March 2011
www.richtek.com
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
RT8268
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR) also begins to charge or discharge
COUT generating a feedback error signal for the regulator
to return VOUTto its steady-state value. During this recovery
time, VOUT can be monitored for overshoot or ringing that
would indicate a stability problem.
Thermal Considerations
The maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junction to ambient. The maximum power dissipation can
be calculated by following formula :
PD(MAX) = ( TJ(MAX) - TA ) / θJA
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT8268, the maximum junction temperature is 125°C. The
junction to ambient thermal resistance θJA for MSOP-10
(Exposed Pad) package is 86°C/W and for SOP-8 is
120°C/W on the standard JEDEC 51-7 four-layers thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by following formula :
PD(MAX) = (125°C − 25°C) / (86°C/W) = 1.163W for
MSOP-10 (Exposed Pad)
PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
SOP-8
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For RT8268 packages, the Figure 3 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
dissipation allowed.
1.2
1.1 Four Layer PCB
1
0.9 SOP-8
MSOP-10 (Exposed Pad)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 25 50 75 100 125
Ambient Temperature ((°°CC)
Figure 3. Derating Curves for RT8268 Packages
Layout Consideration
Follow the PCB layout guidelines for optimal performance
of the RT8268.
` Keep the traces of the main current paths as short and
wide as possible.
` Put the input capacitor as close as possible to the device
pins (VIN and GND).http://www.DataSheet4U.net/
` LX node is with high frequency voltage swing and should
be kept at small area. Keep sensitive components away
from the LX node to prevent stray capacitive noise pick-
up.
` Place the feedback components to the FB pin as close
as possible.
` The GND and Exposed Pad should be connected to a
strong ground plane for heat sinking and noise protection.
DS8268-02 March 2011
www.richtek.com
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8268.PDF ] | |
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