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PDF RT8288A Data sheet ( Hoja de datos )
| Número de pieza | RT8288A | |
| Descripción | 500kHz Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8288A
4A, 21V 500kHz Synchronous Step-Down Converter
General Description
The RT8288A is a synchronous step-down regulator with
an internal power MOSFET. It achieves 4A of continuous
output current over a wide input supply range with excellent
load and line regulation. Current mode operation provides
fast transient response and eases loop stabilization.
Fault condition protection includes cycle-by-cycle current
limiting and thermal shutdown. An internal soft-start
minimizes external parts count and internal compensation
circuitry.
The RT8288A requires a minimal number of readily
available external components, providing a compact
solution.
Ordering Information
RT8288A
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Note :
Lead Plating System
Z : ECO (Ecological Element with
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
RT8288A
ZSPYMDNN
RT8288AZSP : Product Number
YMDNN : Date Code
Features
z 4A Output Current
z Internal Soft-Start
z 120mΩ/40mΩ Internal Power MOSFET Switch
z Internal Compensation Minimizes External Parts
Count
z Fixed 500kHz Frequency
z Thermal Shutdown Protection
z Cycle-by-Cycle Over Current Protection
z Wide 4.5V to 21V Operating Input Range
z Adjustable Output from 0.808V to 15V
z Available in an SOP-8 (Exposed Pad) Package
z RoHS Compliant and Halogen Free
Applications
z Distributive Power Systems
z Battery Charger
z DSL Modems
z Pre-Regulator for Linear Regulators
Pin Configurationshttp://www.DataSheet4U.net/
(TOP VIEW)
VIN
SW
SW
BOOT
8
27
GND
36
9
45
GND
VCC
FB
EN
SOP-8 (Exposed Pad)
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8288A
Parameter
Under Voltage Lockout
Threshold
Under Voltage Lockout
Threshold Hysteresis
VCC Regulator
VCC Load Regulation
Soft-Start Period
Thermal Shutdown
Thermal Shutdown Hysteresis
Symbol
Test Conditions
VUVLO
VIN Rising
ΔVUVLO
tSS
TSD
ΔTSD
ICC = 5mA
Min Typ Max Unit
3.8 4 4.2 V
-- 400 -- mV
-- 5 -- V
-- 5 -- %
-- 2 -- ms
-- 150 -- °C
-- 30 -- °C
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and 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 may
affect device reliability.bsolute maximum rating conditions for extended periods may remain possibility to affect device
reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at 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/
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
RT8288A
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT / 2. This simple worst case condition is commonly
used for design because even significant deviations do
not offer much relief.
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.
For the input capacitor, one 22μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to Table 3 for more detail.
Location
CIN
CIN
COUT
COUT
COUT
COUT
Table 3. Suggested Capacitors for CIN and COUT
Component Supplier
MURATA
TDK
MURATA
TDK
MURATA
TDK
Part No.
GRM32ER71C226M
C3225X5R1C226M
GRM31CR60J476M
C3225X5R0J476M
GRM32ER71C226M
C3225X5R1C226M
Capacitance (μF)
22
22
47
47
22
22
Case Size
1210
1210
1206
1210
1210
1210
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.
The output ripple, ΔVOUT, is determined by :
ΔVOUT
≤
ΔIL
⎡⎢⎣ESR +
1
8fCOUT
⎤
⎥⎦
Higher values, lower 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 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.
Thermal Shutdown
Thermal shutdown is implemented to prevent the chip from
operating at excessively high temperatures. When the
junction temperature is higher than 150°C, the chip will
shut down the switching operation. The chip will
automatically resume switching, once the junction
http://www.DataSheet4U.net/
temperature cools down by approximately 30°C.
EMI Consideration
Since parasitic inductance and capacitance effects in PCB
circuitry would cause a spike voltage on SW pin when
high side MOSFET is turned-on/off, this spike voltage on
SW may impact on EMI performance in the system. In
order to enhance EMI performance, there are two methods
to suppress the spike voltage. One way is by placing an
R-C snubber (RS*, CS*) between SW and GND and locating
them as close as possible to the SW pin, as shown in
Figure 5. Another method is by adding a resistor in series
with the bootstrap capacitor, CBOOT, but this method will
decrease the driving capability to the high side MOSFET.
It is strongly recommended to reserve the R-C snubber
during PCB layout for EMI improvement. Moreover,
reducing the SW trace area and keeping the main power
in a small loop will be helpful on EMI performance. For
detailed PCB layout guide, please refer to the section
Layout Considerations.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8288A-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
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11 Page | ||
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