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PDF RT8278 Data sheet ( Hoja de datos )
| Número de pieza | RT8278 | |
| Descripción | 3MHz Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de RT8278 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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RT8278
2A, 24V, 3MHz Step-Down Converter
General Description
The RT8278 is a high voltage buck converter that can
support an input voltage range from 4.5V to 24V with output
current up to 2A. Current mode operation provides fast
transient response and eases loop stabilization.
The chip provides protection functions such as cycle-by-
cycle current limiting and thermal shutdown protection.
In shutdown mode, the regulator only draws 25μA of
supply current. The RT8278 is available in a SOP-8
(Exposed Pad) package.
Ordering Information
RT8278
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
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
RT8278
GSPYMDNN
RT8278GSP : Product Number
YMDNN : Date Code
Features
Wide Operating Input Range : 4.5V to 24V
Adjustable Output Voltage Range : 0.8V to 15V
Output Current up to 2A
25μA Low Shutdown Current
High Efficiency up to 90% at 2.2MHz
Programmable Frequency : 220kHz to 3MHz
Internal Soft-Start
Stable with Low ESR Output Ceramic Capacitors
Thermal Shutdown Protection
Cycle-By-Cycle Over Current Protection
RoHS Compliant and Halogen Free
Applications
DSL Modem for ADSL2+ Standard
Distributed Power Systems
Pre-Regulator for Linear Regulators
Pin Configurations
http://www.DataSheet4U.net/
(TOP VIEW)
BOOT
VIN
SW
GND
8
27
GND
36
9
45
RT
EN
COMP
FB
SOP8 (Exposed Pad)
Typical Application Circuit
VIN
4.5V to 24V
Chip Enable
CIN
10µF
2 VIN
BOOT 1
7 EN
RT8278
SW 3
8 RT
RRT
24K
4,
9 (Exposed Pad) GND
FB 5
COMP 6
DS8278-02 March 2011
CBOOT L
10nF 2.2µH
D
B220A
R1
31.6k
VOUT
3.3V/2A
COUT
22µF
1CnCF 3R6Ck
R2
10k
NCCP
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8278
P ara meter
EN T hreshold
Vol ta ge
Lo gic -Hig h
L ogi c-Lo w
Enable Pull Up Current
Quiescent Current
Shutdown Current
Thermal Shutdown
Symbol
VIH
VIL
Test Conditions
IQ
I SHD N
VEN = 2V, VFB = 1V
VEN = 0V
Min Typ Max Unit
1.4 --
--
V
-- -- 0.4
-- 1 -- μA
-- 0.8 1 mA
-- 25 -- μA
-- 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 natural convection at TA = 25°C on a high effective thermal conductivity four-layer test board of
JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the
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/
DS8278-02 March 2011
www.richtek.com
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
RT8278
Table2. Suggested Inductors for Typical Application
Circuit
Component
Supplier
TDK
Series
VL C604 5
Dimensions
(mm)
6 x 6 x 4.5
TDK
S LF12 565
12.5 x 12.5 x
6.5
TAI YO
YUDEN
NR80 40
8x8 x4
Diode Selection
When the power switch turns off, the path for the current
is through the diode connected between the switch output
and ground. This forward biased diode must have a minimal
voltage drop and recovery time. Schottky diodes are
recommended and should be able to handle those current.
The reverse voltage rating of the diode should be greater
than the maximum input voltage, and the current rating
should be greater than the maximum load current. For
details, please refer to Table 3.
Table 3. Suggested Diode
Component
Supplier
Series
VRRM (V) IOUT (A)
DIODES B330A 30
3
Package
SMA
DIODES B220A 20 2 SMA
PANJIT SK22 20
2 DO-214AA
PANJIT SK23 30
2 DO-214AA
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
IRMS
=
IOUT(MAX)
VOUT
VIN
VIN
VOUT
−1
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT / 2. This simple worst-case condition is
commonly used for design.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
DS8278-02 March 2011
For the input capacitor, one 10μF low ESR ceramic
capacitors is recommended. For the recommended
capacitor, please refer to Table 4 below for more details.
The selection of COUT is determined by the required ESR
to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for COUT selection to ensure that the control loop is stable.
Loop stability can be checked by viewing the load transient
response as described in a later section.
The output ripple, ΔVOUT , is determined by :
ΔVOUT
≤
ΔIL
⎡⎢⎣ESR
+
1
8fCOUT
⎤
⎥⎦
The output ripple will be highest at the maximum input
voltage since ΔIL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount packages.
Special polymer capacitors offer very low ESR value.
However, it provides lower capacitance density than other
types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
passhttp://www.DataSheet4U.net/ the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Nevertheless, high value low cost ceramic capacitors are
now becoming available in smaller case sizes. Their high
ripple current, high voltage rating and low ESR make them
ideal for switching regulator applications. However, care
must be taken when these capacitors are used at the
input and output. When a ceramic capacitor is used at
the input and the power is supplied by a wall adapter through
long wires, a load step at the output can induce ringing at
the input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
www.richtek.com
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet RT8278.PDF ] | |
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