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PDF RT8295B Data sheet ( Hoja de datos )
| Número de pieza | RT8295B | |
| Descripción | 1.2MHz Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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RT8295B
2A, 23V, 1.2MHz Synchronous Step-Down Converter
General Description
Features
The RT8295B is a high-efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 2A
output current from a 4.5V to 23V input supply. The
RT8295B'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 RT8295B 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 RT8295B is available in a
SOP-8 (Exposed Pad) package.
Ordering Information
RT8295B
Package Type
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)
H : UVP Hiccup
L : UVP Latch-Off
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.
z ±1.5% High Accuracy Feedback Voltage
z 4.5V to 23V Input Voltage Range
z 2A Output Current
z Integrated N-MOSFET Switches
z Current Mode Control
z Fixed Frequency Operation : 1.2MHz
z Adjustable Output from 0.8V to 15V
z Up to 95% Efficiency
z Programmable Soft-Start
z Stable with Low-ESR Ceramic Output Capacitors
z Cycle-by-Cycle Over Current Protection
z Input Under Voltage Lockout
z Output Under Voltage Protection
z Thermal Shutdown Protection
z RoHS Compliant and Halogen Free
Applications
z Wireless AP/Router
z Set-Top-Box
Industrial and Commercial Low Power Systemshttp://www.DataSheet4U.net/
z
z LCD Monitors and TVs
z Green Electronics/Appliances
z Point of Load Regulation of High-Performance DSPs
Pin Configurations
(TOP VIEW)
BOOT
VIN
SW
GND
8
27
GND
36
9
45
SS
EN
COMP
FB
Marking Information
SOP-8 (Exposed Pad)
RT8295BxGSP
RT8295Bx
GSPYMDNN
RT8295BxGSP : Product Number
x : H or L
YMDNN : Date Code
RT8295BxZSP
RT8295Bx
ZSPYMDNN
RT8295BxZSP : Product Number
x : H or L
YMDNN : Date Code
DS8295B-03 March 2011
www.richtek.com
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
RT8295B
Parameter
Symbol
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
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
-- 13.5 --
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/
DS8295B-03 March 2011
www.richtek.com
5
datasheetpdf-http://www.DataSheet4U.net/
5 Page 
RT8295B
response as described in a later section.
The output ripple, ∆VOUT , is determined by :
∆VOUT
≤
∆IL
ESR
+
1
8fCOUT
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.
The output ripple will be highest at the maximum input
voltage since ∆IL 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 av ai labl e in surf ace 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
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 charged
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
h to sut ppret ss thpe spik: e vo/ ltage/ . Onew wayw is byw plac. ing aD n
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 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.
VIN
4.5V to 23V
Chip Enable
REN*
CEN*
CIN
10µF
2 VIN
BOOT 1
RT8295B
7 EN
SW 3
8 SS
CSS
0.1µF
4,
9 (Exposed Pad)
GND
FB 5
COMP 6
RBOOT*
CBOOT
100nF
3.6LµH
RS*
CS*
CC
0.82nF
RC
32k
R1
75k
R2
24k
VOUT
3.3V/2A
COUT
22µFx2
a
t
* : Optional
CP
NC
Figure 5. Reference Circuit with Snubber and Enable Timing Control
DS8295B-03 March 2011
www.richtek.com
11
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11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT8295B.PDF ] | |
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