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PDF RT7252B Data sheet ( Hoja de datos )
| Número de pieza | RT7252B | |
| Descripción | (RT7252A/B) Synchronous Step-Down Converter | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT7252A/B
2A, 17V, 340/800kHz Synchronous Step-Down Converter
General Description
The RT7252A/B is a high efficiency, monolithic
synchronous step-down DC/DC converter that can operate
at 340kHz/800kHz, while delivering up to 2A output current
from a 4V to 17V input supply. The RT7252A/B's current
mode architecture allows the transient response to be
optimized. 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, output over voltage
protection and thermal shutdown. The low current (<5μA)
shutdown mode provides output disconnection, enabling
easy power management in battery-powered systems. The
RT7252A/B is available in a SOP-8 (Exposed Pad)
package.
Ordering Information
RT7252A/B
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
A : 340kHz
B : 800kHz
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.
Marking Information
RT7252AZSP
RT7252A
ZSPYMDNN
RT7252AZSP : Product Number
YMDNN : Date Code
Features
z 4V to 17V Input Voltage Range
z 2A Output Current
z Internal N-MOSFETs
z Current Mode Control
z Fixed Frequency Operation : 340kHz/800kHz
z Output Adjustable from 0.8V to 12V
z Up to 95% Efficiency
z Internal Compensation
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 Output Over Voltage Protection
z Power Good Indicator
z Thermal Shutdown Protection
z RoHS Compliant and Halogen Free
Applications
z Industrial and Commercial Low Power Systems
z Computer Peripherals
z LCD Monitors and TVs
z Green Electronics/Appliances
z Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Pin Configurations
(TOP VIEW)
SW
VIN
BOOT
EN
8
27
GND
36
9
45
NC
GND
PGOOD
FB
SOP-8 (Exposed Pad)
RT7252BZSP
RT7252B
ZSPYMDNN
RT7252BZSP : Product Number
YMDNN : Date Code
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7252A/B-01 April 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.datasheet4u.com/
1 page  
RT7252A/B
Parameter
Symbol
Test Conditions
Minimum On-Time
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Threshold Hysteresis
tON
VUVLO
ΔVUVLO
EN Threshold
Voltage
Logic-High VIH
Logic-Low VIL
EN Pull Low Current
VEN = 2V, VFB = 1V
Soft-Start Period
tSS
Thermal Shutdown
TSD
Thermal Shutdown Hysteresis ΔTSD
Power Good Threshold Rising
Power Good Threshold
Hysteresis
Power Good Pull Down
Resistance
Output OVP Threshold
Output OVP Propagation
Delay
Min Typ Max Unit
-- 100 --
ns
-- 3.5 --
V
-- 200 --
2.5 --
--
-- -- 0.4
-- 1 --
-- 1 --
-- 150 --
-- 15 --
-- 0.7 --
-- 130 --
mV
V
μA
ms
°C
°C
V
mV
-- 12 --
Ω
-- 125 -- %VREF
-- 10 --
μs
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.
DS7252A/B-01 April 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.datasheet4u.com/
5 Page 
Application Information
The RT7252A/B is a synchronous high voltage buck
converter that can support the input voltage range from
4V to 17V and the output current can be up to 2A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
VOUT
FB
RT7252A/B
GND
R1
R2
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
VOUT
=
VFB
⎛⎜⎝1+
R1
R2
⎞
⎟⎠
where VFB is the feedback reference voltage (0.8V typ.).
External Bootstrap Diode
Connect a 10nF low ESR ceramic capacitor between the
BOOT pin and SW pin. This capacitor provides the gate
driver voltage for the high side MOSFET. It is recommended
to add an external bootstrap diode between an external
5V and the BOOT pin for efficiency improvement when
input voltage is lower than 5.5V or duty ratio is higher
than 65%. The bootstrap diode can be a low cost one
such as 1N4148 or BAT54. The external 5V can be a 5V
fixed input from system or a 5V output of the RT7252A/B.
Note that the external boot voltage must be lower than
5.5V
5V
BOOT
RT7252A/B
SW
10nF
Figure 2. External Bootstrap Diode
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS7252A/B-01 April 2012
RT7252A/B
Over Voltage Protection (OVP)
The RT7252A/B provides over voltage protection function
when output voltage is over 125%. The internal MOS will
be turned off. The control will return to normal operation if
over voltage condition is removed.
Under Voltage Protection (UVP)
Latch-Off Mode
For the RT7252A/B, it provides Hiccup Mode Under
Voltage Protection (UVP). When the FB voltage drops
below 50% of the feedback reference voltage, VFB, the
UVP function will be triggered and the RT7252A/B will
shut down for a period of time and then recover
automatically. The Hiccup Mode UVP can reduce input
current in short-circuit conditions.
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 = 0.2(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= ⎢
VOUT
⎤⎡
⎥ × ⎢1−
VOUT
⎤
⎥
⎢⎣ f × ΔIL(MAX) ⎥⎦ ⎢⎣ VIN(MAX) ⎥⎦
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
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet RT7252B.PDF ] | |
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