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PDF RT8294 Data sheet ( Hoja de datos )
| Número de pieza | RT8294 | |
| Descripción | 340kHz Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8294
2A, 23V, 340kHz Synchronous Step-Down Converter
General Description
The RT8294 is a high efficiency, monolithic synchronous
step-downDC/DC converter that can deliver up to 2A output
current from a 4.5V to 23V input supply. The RT8294'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. The RT8294 also provides under voltage protection
and thermal shutdown protection. The low current (< 3µA)
shutdown mode provides output disconnection, enabling
easy power management in battery-powered systems. The
RT8294 is available in SOP-8 and SOP-8 (Exposed Pad)
packages.
Ordering Information
RT8294
Package Type
S : SOP-8
SP: SOP-8(Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
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.
Features
l ±1.5% High Accuracy Feedback Voltage
l Input Voltage Range : 4.5V to 23V
l 2A Output Current
l Integrated N-MOSFETs
l Current Mode Control
l 340kHz Fixed Frequency Operation
l Output Adjustable Voltage Range : 0.923V to 20V
l Efficiency Up to 95%
l Programmable Soft-Start
l Stable with Low ESR Ceramic Output Capacitors
l Cycle-by Cycle Over Current Protection
l Input Under Voltage Lockout
l Output Under Voltage Protection
l Thermal Shutdown Protection
l RoHS Compliant and Halogen Free
Applications
l Wireless AP/Router
l Set-Top-Box
http://www.DataSheet4U.net/
l Industrial and Commercial Low Power Systems
l LCD Monitors and TVs
l Green Electronics/Appliances
l Point of Load Regulation of High-Performance DSPs
Pin Configurations
(TOP VIEW)
BOOT
VIN
SW
GND
8
27
36
45
SOP-8
SS
EN
COMP
FB
BOOT
VIN
SW
GND
8
27
GND
36
9
45
SS
EN
COMP
FB
SOP-8 (Exposed Pad)
DS8294-02 March 2011
www.richtek.com
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datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8294
Parameter
EN Input Threshold
Voltage
Logic High
Logic Low
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Hysteresis
Soft-Start Current
Soft-Start Period
Thermal Shutdown
Symbol
VIH
VIL
VUVLO
∆VUVLO
ISS
tSS
TSD
Test Conditions
VIN Rising
VSS = 0V
CSS = 0.1µF
Min Typ Max Unit
2.7 -- 5.5
V
-- -- 0.4
3.8 4.2 4.5
V
-- 320 -- mV
-- 6 -- µA
-- 15.5 --
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 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/
DS8294-02 March 2011
www.richtek.com
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datasheet pdf - http://www.DataSheet4U.net/
5 Page 
RT8294
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 ∆ILOAD (ESR) and COUT also begins to be charge
or discharged to generate 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.
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 between SW and GND and locating them as
close as possible to the SW pin (see 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 PCBhttp://www.DataSheet4U.net/
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.
VIN
4.5V to 23V
Chip Enable
REN*
CEN*
CIN
10µF
2 VIN
BOOT 1
7 EN
RT8294
SW 3
8 SS
CSS
0.1µF
4,
Exposed Pad(9)
GND
FB 5
COMP 6
RBOOT*
CBOOT
10nF
10LµH
RS*
CS*
CC
3.3nF
RC
13k
VOUT
3.3V/2A
R1 COUT
26.1k 22µFx2
R2
10k
* : Optional
CP
NC
Figure 5. Reference Circuit with Snubber and Enable Timing Control
DS8294-02 March 2011
www.richtek.com
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT8294.PDF ] | |
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