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PDF RT8253B Data sheet ( Hoja de datos )
| Número de pieza | RT8253B | |
| Descripción | 1.2MHz Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8253B
3A, 23V, 1.2MHz Synchronous Step-Down Converter
General Description
Features
The RT8253B is a high-efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 3A
output current from a 4.5V to 23V input supply. The
RT8253B's current mode architecture and external
compensation allow the transient response to be
optimized over a wide range of loads and output capacitors.
Cycle-by-cycle current limit provides protection against
shorted outputs and soft-start eliminates input current
surge during start-up. Fault conditions also include output
under voltage protection and thermal shutdown protection.
The low current (<3μA) shutdown mode provides output
disconnect, enabling easy power management in battery-
powered systems. The RT8253B is available in a
SOP-8 (Exposed Pad) package.
Ordering Information
RT8253B
±1.5% High Accuracy Feedback Voltage
4.5V to 23V Input Voltage Range
3A Output Current
Integrated N-MOSFET Switches
Current Mode Control
Fixed Frequency Operation : 1.2MHz
Adjustable Output from 0.8V to 20V
Up to 95% Efficiency
Programmable Soft-Start
Stable with Low-ESR Ceramic Output Capacitors
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Applications
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
External Storage Device
Wireless AP/Router
Note :
Lead Plating System
Set-Top-Boxhttp://www.DataSheet4U.net/
G : Green (Halogen Free and Pb Free) Industrial and Commercial Low Power Systems
H : UVP Hiccup
L : UVP Latch-Off
LCD Monitors and TVs
Green Electronics/Appliances
Richtek products are :
Point of Load Regulation of High-Performance DSPs
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Pin Configurations
` Suitable for use in SnPb or Pb-free soldering processes.
(TOP VIEW)
Marking Information
RT8253B
xGSPYMDNN
RT8253BGSP : Product Number
x : H or L
YMDNN : Date Code
BOOT
VIN
SW
GND
8
27
GND
36
9
45
SS
EN
COMP
FB
SOP-8 (Expoaed Pad)
DS8253B-02 March 2011
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8253B
Parameter
EN Threshold Logic-High
Voltage
Logic-Low
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Hysteresis
Soft-Start Current
Soft-Start Period
Thermal Shutdown
Symbol
VIH
VIL
Test Conditions
VIN Rising
VSS = 0V
CSS = 0.1μF
TSD
Min Typ Max Unit
2.7 -- 5.5
V
-- -- 0.4
3.8 4.2 4.5
V
-- 320 --
-- 6 --
-- 13.5 --
-- 150 --
mV
μA
ms
°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 expose pad for
SOP-8 (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/
DS8253B-02 March 2011
www.richtek.com
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
RT8253B
IRMS
=
IOUT(MAX)
VOUT
VIN
VIN −1
VOUT
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, two 10μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to Table 3 for more detail.
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
pass 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.
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.
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 VOUT to its steady-state value. During this
recovery time, VOUT can be monitored for overshoot or
ringing that would indicate a stability problem.http://www.DataSheet4U.net/
EMI Consideration
Since parasitic inductance and capacitance effects in PCB
circuitry would cause a spike voltage on the 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 is to place an R-C
snubber between SW and GND and make them as close
as possible to the SW pin (see Figure 5). Another method
is 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 of Layout Consideration.
DS8253B-02 March 2011
www.richtek.com
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8253B.PDF ] | |
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