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PDF RT7247B Data sheet ( Hoja de datos )
| Número de pieza | RT7247B | |
| Descripción | Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT7247B
2A, 18V, 1.2MHz Synchronous Step-Down Converter
General Description
The RT7247B is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 2A
output current from a 4.5V to 18V input supply. The
RT7247B's current mode architecture and external
compensation allow the transient response to be
optimized over a wide input range and loads. Cycle-by-
cycle current limit provides protection against shorted
outputs, and soft-start eliminates input current surge during
start-up. The RT7247B 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 RT7247B is available in
an SOP-8 (Exposed Pad) package.
Marking Information
RT7247BxGSP : Product Number
RT7247Bx
GSPYMDNN
x : H or L
YMDNN : Date Code
Features
±1.5% High Accuracy Reference Voltage
4.5V to 18V Input Voltage Range
2A Output Current
Integrated N-MOSFET Switches
Current Mode Control
Fixed Frequency Operation : 1.2MHz
Output Adjustable from 0.8V to 12V
Stable with Low ESR Ceramic Output Capacitors
Up to 95% Efficiency
Programmable Soft-Start
Cycle-by-Cycle Over Current Limit
Input Under Voltage Lockout
Output Under Voltage Protection
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Applications
Wireless AP/Router
Set-Top-Box
Industrial and Commercial Low Power Systems
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation of High-Performance DSPs
Simplified Application Circuit
VIN
Chip Enable
VIN BOOT
CIN RT7247B
SW
EN
SS
CSS
GND
FB
COMP
CBOOT
L
CC RC
VOUT
R1
COUT
R2
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7247B-01 September 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT7247B
Parameter
EN Input 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
VUVLO
ΔVUVLO
ISS
tSS
TSD
Test Conditions
VIN Rising
VSS = 0V
CSS = 0.1μF
Min Typ Max Unit
2 -- 18
V
-- -- 0.4
3.8 4.2 4.5
V
-- 320 --
-- 6 --
-- 13.5 --
-- 150 --
mV
μA
ms
°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.
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.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7247B-01 September 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
RT7247B
Under Voltage Protection
Hiccup Mode
For the RT7247BH, it provides Hiccup Mode Under Voltage
Protection (UVP). When the VFB voltage drops below 0.4V,
the UVP function will be triggered to shut down switching
operation. If the UVP condition remains for a period, the
RT7247BH will retry automatically. When the UVP
condition is removed, the converter will resume operation.
The UVP is disabled during soft-start period.
Hiccup Mode
VOUT
(500mV/Div)
IL
(2A/Div)
Time (50ms/Div)
Figure 5. Hiccup Mode Under Voltage Protection
Latch-Off Mode
For the RT7247BL, it provides Latch-Off Mode Under
Voltage Protection (UVP). When the FB voltage drops
below half of the feedback reference voltage, VFB, UVP
will be triggered and the RT7247BL will shut down in Latch-
Off Mode. In shutdown condition, the RT7247BL can be
reset by EN pin or power input VIN.
Latch-Off Mode
VOUT
(2V/Div)
IL
(2A/Div)
Time (50ms/Div)
Figure 6. Latch-Off Mode Under Voltage Protection
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7247B-01 September 2012
Over Temperature Protection
The RT7247B features an Over Temperature Protection
(OTP) circuitry to prevent from overheating due to
excessive power dissipation. The OTP will shut down
switching operation when junction temperature exceeds
150°C. Once the junction temperature cools down by
approximately 20°C, the converter will resume operation.
To maintain continuous operation, the maximum junction
temperature should be lower than 125°C.
Inductor Selection
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔIL increases with higher VIN
and decreases with higher inductance.
ΔIL
=
⎡
⎢⎣
VOUT
f ×L
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN
⎤
⎥⎦
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
the highest efficiency operation. However, it requires a
large inductor to achieve this goal.
For the ripple current selection, the value of ΔIL= 0.24(IMAX)
will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
L
=
⎡
⎢⎣
f
×
VOUT
ΔIL(MAX)
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN(MAX)
⎤
⎥⎦
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference.
Table 2. Suggested Inductors for Typical
Application Circuit
Component
Supplier
Ser ie s
Dimensions
(mm)
TDK
VLF10045 10 x 9.7 x 4.5
TDK
TAIYO
YUDEN
SLF12565
NRS8040
12.5 x 12.5 x 6.5
8x8x4
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet RT7247B.PDF ] | |
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