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PDF RT7237C Data sheet ( Hoja de datos )
| Número de pieza | RT7237C | |
| Descripción | Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT7237C
2A, 18V, 800kHz Synchronous Step-Down Converter
General Description
The RT7237C 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
RT7237C'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 RT7237C 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 RT7237C is available in
an SOP-8 (Exposed Pad) package.
Marking Information
RT7237CH
GSPYMDNN
RT7253CHGSP : Product Number
YMDNN : Date Code
Features
z ±1.5% High Accuracy Reference Voltage
z 4.5V to 18V Input Voltage Range
z 2A Output Current
z Integrated N-MOSFET Switches
z Current Mode Control
z Fixed Frequency Operation : 800kHz
z Output Adjustable from 0.8V to 12V
z Stable with Low ESR Ceramic Output Capacitors
z Up to 95% Efficiency
z Programmable Soft-Start
z Cycle-by-Cycle Over Current Limit
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
z Industrial and Commercial Low Power Systems
z LCD Monitors and TVs
z Green Electronics/Appliances
z Point of Load Regulation of High-Performance DSPs
Simplified Application Circuit
VIN
Chip Enable
VIN BOOT
CIN RT7237C
SW
EN
SS
CSS
GND
FB
COMP
CBOOT
L
CC RC
VOUT
R1
COUT
R2
CP
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7237C-04 November 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT7237C
Parameter
Symbol
Minimum On-Time
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
tON
VIH
VIL
VUVLO
ΔVUVLO
ISS
tSS
TSD
Test Conditions
VIN Rising
VSS = 0V
CSS = 0.1μF
Min Typ Max Unit
-- 100 --
ns
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.
DS7237C-04 November 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
RT7237C
Under Voltage Protection
Hiccup Mode
For the RT7237C, 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
RT7237C 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
(2V/Div)
ILX
(2A/Div)
IOUT = Short
Time (50ms/Div)
Figure 5. Hiccup Mode Under Voltage Protection
Over Temperature Protection
The RT7237C 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
⎤
⎥⎦
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7237C-04 November 2012
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
Series
Dimensions
(mm)
TDK
VLF10045 10 x 9.7 x 4.5
TDK
SLF12565 12.5 x 12.5 x 6.5
TAIYO
YUDEN
NR8040
8x8x4
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
approximate RMS current is given :
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 suggested. For the
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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