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PDF RT8120 Data sheet ( Hoja de datos )
| Número de pieza | RT8120 | |
| Descripción | Single-Phase Synchronous Buck PWM Controller | |
| Fabricantes | Richtek | |
| Logotipo |  |
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®
RT8120
Single-Phase Synchronous Buck PWM Controller
General Description
The RT8120 is a single-phase synchronous buck PWM
DC/DC controller designed to drive two N-MOSFET. It
provides a highly accurate, programmable output voltage
precisely regulated to low voltage requirements with an
internal 0.8V ±1% ( option for 0.6V ±1.5%) reference. The
RT8120 uses a single feedback loop voltage mode PWM
control for fast transient response. An oscillator with fixed
frequency 300kHz reduces the external inductor and
capacitor component size for saving PCB board area. The
RT8120 provides fast transient response to satisfy high
current output applications while minimizing external
components. It is suitable for high performance graphic
processors,DDR and VTT power. The RT8120 incorporates
an externally compensated error amplifier and an internal
soft-start and output enable. The RT8120 comes in
SOP-8 and SOP-8 (Exposed Pad) packages.
Ordering Information
RT8120
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)
Reference Voltage
A/C : 0.6V
B/D : 0.8V
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
z Wide Input Voltage Range : 3V to 13.2V
z Embedded Switching Boot Diode
z 0.8V ±1%, 0.6V ±1.5% Internal Reference
z Shoot-Through Protection and Short Pulse Free
Technology for Gate Drivers
z Fixed Frequency 300kHz
z Internal Soft-Start
z Over Current Protection by Sensing MOSFET RDS(ON)
z Enable/Shutdown Control
z Drives Two N-MOSFETs
z Full Duty Cycle : 0% to 85%
z Fast Transient Response
z Voltage Mode PWM Control with External
Feedback Loop Compensation
z Pinless LGATE Over Current Setting (LGOCS)
z Under Voltage Protection
z SOP-8 and SOP-8 (Exposed Pad) Packages
z RoHS Compliant and Halogen Free
Applications
z System (Graphic, MB) with 5V or 12V Power
z Graphic Cards (AGP 8X, 4X, PCI Express*16)
z 3.3V to 12V Input DC/DC Regulators
z Low Voltage Distributed Power Supplies
Pin Configurations
(TOP VIEW)
BOOT
UGATE
GND
LGATE/OCSET
2
3
4
8 PHASE
7 COMP/EN
6 FB
5 VCC
SOP-8
BOOT
UGATE
GND
LGATE/OCSET
8
27
GND
36
9
45
PHASE
COMP/EN
FB
VCC
SOP-8 (Exposed Pad)
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8120-06 September 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
Free Datasheet http://www.Datasheet4U.com
1 page  
RT8120
Absolute Maximum Ratings (Note 1)
z VCC to GND, VCC --------------------------------------------------------------------------------------- 15V
z BOOT to PHASE, VBOOT−PHASE ----------------------------------------------------------------------- 15V
z PHASE to GND
DC ------------------------------------------------------------------------------------------------------------ −0.5V to 15V
< 20ns ------------------------------------------------------------------------------------------------------ −8V to 25V
z UGATE to PHASE
DC ------------------------------------------------------------------------------------------------------------ −0.3V to (VBOOT−PHASE + 0.3V)
< 20ns ------------------------------------------------------------------------------------------------------ −5V to (VBOOT−PHASE + 5V)
z LGATE to GND
DC ------------------------------------------------------------------------------------------------------------ −0.3V to (VCC + 0.3V)
< 20ns ------------------------------------------------------------------------------------------------------ −5V to (VCC + 5V)
z Other Pins -------------------------------------------------------------------------------------------------- −0.3V to 7V
z Power Dissipation, PD @ TA = 25°C
SOP-8 ------------------------------------------------------------------------------------------------------- 0.833W
SOP-8 (Exposed Pad) ---------------------------------------------------------------------------------- 1.333W
z Package Thermal Resistance (Note 2)
SOP-8, θJA ------------------------------------------------------------------------------------------------ 120°C/W
SOP-8 (Exposed Pad), θJA ---------------------------------------------------------------------------- 75°C/W
SOP-8 (Exposed Pad), θJC ---------------------------------------------------------------------------- 15°C/W
z Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------- 260°C
z Junction Temperature ------------------------------------------------------------------------------------ 150°C
z Storage Temperature Range --------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Model) ----------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
z Supply Input Voltage, VIN ------------------------------------------------------------------------------ 3V to 13.2V
z Control Input Voltage, VCC ---------------------------------------------------------------------------- 4.5V to 13.2V
z Junction Temperature Range --------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range --------------------------------------------------------------------------- −40°C to 85°C
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8120-06 September 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
Free Datasheet http://www.Datasheet4U.com
5 Page 
RT8120
LGATE Over Current Setting (LGOCS)
Over current threshold is externally programmed by adding
a resistor (ROCSET) between LGATE and GND. Once VCC
exceeds the POR threshold, an internal current source
IOCSET flows through ROCSET. The voltage across ROCSET is
stored as the over current protection threshold VOCSET.
After that, the current source is switched off. ROCSET can
be determined using the following equation :
ROCSET
=
IVALLEY x RLGDS(ON)
IOCSET
where IVALLEY represents the desired inductor OCP trip
current (valley inductor current).
If ROCSET is not present, there is no current path for IOCSET
to build the OCP threshold. In this situation, the OCP
threshold is internally preset to 375mV (typical).
Under Voltage Protection (UVP)
The voltage on the FB pin is monitored for under voltage
protection. If the FB voltage is lower than the UVP threshold
(typically 75% x VREF) during normal operation, UVP will
be triggered. When the UVP is triggered, both UGATE
and LGATE go low. The controller enters hiccup mode
until the UVP condition is removed.
Output Voltage Setting
The RT8120 allows the output voltage of the DC/DC
converter to be adjusted from 0.8V (option for 0.6V) to
85% of VIN via an external resistor divider. It will try to
maintain the feedback pin at internal reference voltage
(0.8V, with option for 0.6V).
VOUT
RFB1
FB
RFB2
Figure 3. Output Voltage Setting
According to the resistor divider network above, the output
voltage is set as :
VOUT
= VREF
x
⎛
⎜1 +
⎝
RFB1
RFB2
⎞
⎟
⎠
MOSFET Drivers
The RT8120 integrates high current gate drivers for the
two N-MOSFETs to obtain high efficiency power conversion
in synchronous buck topology. A dead time is used to
prevent crossover conduction for the high side and low
side MOSFETs. Because both gate signals are off during
dead time, the inductor current freewheels through the
body diode of the low side MOSFET. The freewheeling
current and the forward voltage of the body diode contribute
to power loss. The RT8120 employs constant dead time
control scheme to ensure safe operation without
sacrificing efficiency. Furthermore, elaborate logic circuit
is implemented to prevent cross conduction.
For high output current applications, two or more power
MOSFETs are usually paralleled to reduce RDS(ON). The
gate driver needs to provide more current to switch on/off
these paralleled MOSFETs. Gate driver with lower source/
sink current capability result in longer rising/ falling time
in gate signals, and therefore higher switching loss.
The RT8120 embeds high current gate drivers to obtain
high efficiency power conversion. The embedded drivers
contribute to the majority of the power dissipation of the
controller. Therefore, SOP package is chosen for its power
dissipation rating. If no gate resistor is used, the power
dissipation of the controller can be approximately
calculated using the following equation :
PDRIVER = fSW x (QG x VBOOT +
QG_LOW SIDE x VDRIVER_LOW SIDE )
where VBOOT represents the voltage across the bootstrap
capacitor and fSW is the switching frequency.
It is important to ensure the package can dissipate the
switching loss and have enough room for safe operation.
Inductor Selection
The inductor plays an importance role in step-down
converters because it stores the energy from the input
power rail and then releases the energy to the load. From
the viewpoint of efficiency, the dc resistance (DCR) of the
inductor should be as small as possible to minimize the
conduction loss. In addition, the inductor covers a
significant proportion of the board space, so its size is
also important. Low profile inductors can save board space
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8120-06 September 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
Free Datasheet http://www.Datasheet4U.com
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet RT8120.PDF ] | |
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