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PDF RT8807A Data sheet ( Hoja de datos )
| Número de pieza | RT8807A | |
| Descripción | Two Phases Synchronous Buck PWM Controller | |
| Fabricantes | Richtek Technology | |
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®
RT8807/A
Two Phases Synchronous Buck PWM Controller
General Description
The RT8807/A is a two phases synchronous Buck PWM
controller with integrated drivers which is optimized for
high-performance graphic microprocessor and computer
applications. The IC integrates a voltage mode PWM
controller, two 5V MOSFET drivers with internal bootstrap
diodes, as well as output current monitoring and protection
functions into the V/WQFN-24L 4x4 package.
The inductor currents are sensed by lossless DCR current
sensing technique for current balance and over current
protection. The RT8807/A also features a reference tracking
mode operation in which the feedback voltage is regulated
and tracks external input reference voltage. Other features
include output current indication, adjustable operating
frequency, adjustable soft-start, power good, external
compensation, and enable/shutdown functions.
Ordering Information
RT8807
Package Type
QV : VQFN-24L 4x4 (V-Type)
(Exposed Pad-Option 1)
RT8807A
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
Package Type
QW : WQFN-24L 4x4 (W-Type)
(Exposed Pad-Option 1)
Lead Plating System
G : Green (Halogen Free and Pb Free)
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
Two-Phase Power Conversion with Single 12V
Power Supply
Embedded 5V Upper Gate Driver and 12V Lower
Gate Driver
Internal Regulated 5V Output
Precise Core Voltage Regulation
Selectable Internal / External Reference
Differential Inductor DCR Current Sense
External Programmable Voltage Droop Control
Enable Control for External Shutdown
Adjustable Operating Frequency
Adjustable Soft Start
Power Good and Output Current Indication
Adjustable Over Current Protection
Over Voltage Protection
Under Voltage Protection
Over Temperature Protection
Proprietary BTR (Boost Transient Response)
Feature Reducing Output Voltage Drop During Load
Transition (For RT8807 Only)
RoHS Compliant and 100% Lead(Pb)-Free
Applications
Middle to High End GPU Core Power
High End Desktop PC Memory Core Power
Low Voltage, High Current DC / DC Converter
Voltage Regulator Modules
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8807/A-02 May 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
1 page  
RT8807/A
EN2B (Pin 5)
EXT_12V Detection Pin. RT8807/A latches high/low status
of this pin in soft start period. If the result is low, RT8807/
A will enter two phase operation. If it's high, RT8807/A
turns off phase2 and operate in single phase only.
CSP1 (Pin 6), CSP2 (Pin 9)
These pins are positive input of current sensing
transconductance amplifiers 1 and 2.
CSN1 (Pin 7), CSN2 (Pin 8)
These pins are negative input of current sensing
transconductance amplifiers 1 and 2.
IOUT/IMAX (Pin10)
Output Current Indication. This pin sends a current out
(IX) referred to the sum of two sensed inductor currents
sense value. Connect this pin through a resistor to ground.
(IOUT = 4 x IX). This pin also sets maximum current limit
threshold.
RT (Pin11)
Frequency Timing Resistor. Connect a resistor from RT
to AGND to set the clock frequency.
COMP (Pin 12)
Compensation Pin. This pin is the output of the error amplifier.
FB (Pin 13)
Feedback Pin. This pin is connected to the PWM converter
output's voltage or a resistor divider. This pin also connects
to the inverting input of error amplifier and the PGOOD/
UV/OV detection circuits.
SS (Pin 14)
Soft-Start Pin. Connect a capacitor from this pin to ground
to set the soft-start interval.
REFIN/EN (Pin 15)
External Reference Input.
If pulled up to 5VCC, internal reference is used (0.6V)
If driven by external voltage ranged from 0.45V to 2.5V,
external reference is used
If pulled below 0.4V, device is disabled.
REFOUT/PGOOD (Pin 16)
Reference Out and Power GOOD. This pin drives 1.15V
out once FB exceeds ~72.5% of the reference voltage
after soft- start ends. This pin keeps at this voltage
regardless of internal or external reference is used.
PHASE1 (Pin 24) PHASE2 (Pin 19)
These pins are return nodes of the high-side driver.
Connect these pins to high-side MOSFET sources
together with the low-side MOSFET drain and the
inductors.
LGATE1 (Pin 23), LGATE2 (Pin 20)
Lower Gate Drivers. Theses pins provide the gate drive for
the converter's low-side MOSFET. Connect these pins to
the low-side MOSFET gate.
DROOP (Pin 21)
Set the load line for droop control. Connect this pin with a
resistor to ground.
VCC (Pin 22)
Provide a 12V supply voltage for the IC. Connect a
10Ω/1uF low pass filter to sustain high PSRR.
PGND [Exposed Pad (25)]
Power ground pin. Tie the synchronous PWM converter's
low-side MOSFET source to this pin.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8807/A-02 May 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
5 Page 
Application Information
The RT8807/A is a dual-phase voltage-mode synchronous
buck controller with embedded MOSFET drivers and
protection functions for low-voltage high-current
applications. The bootstrap diode is integrated into the IC
to reduce the external component count. In addition, the
number of operating phase (two-phase/single-phase) is
selectable to provide user with more flexibility in circuit
design. The inductor current is sensed by innovative DCR
current sensing technique for current balance and over
current protection.
Power On Reset
The RT8807/A initiates its soft start cycle only after the
IC power supply, VCC, and the internal regulated 5VCC
are ready. The internally regulated 5VCC is used for all of
the internal logic control circuit and the embedded high-
side MOSFET driver. The bootstrap diode for the high-
side MOSFET driver is integrated into the IC to reduce
the external component count. In addition, VCC is used
for the low-side MOSFET driver to reduce the RDS(ON) of
the low-side MOSFET for enhanced efficiency
consideration.
The power on reset (POR) circuitry monitors the supply
voltage to ensure that the supply voltage is high enough
for controller's normal operation. Once VCC and 5VCC
exceed the POR rising threshold, the RT8807/A releases
the reset state, and works according to the settings.
Additionally, once any one of these two voltages is lower
than its POR falling threshold value, the chip turns off.
The hysteresis between the rising and falling thresholds
ensures that once the chip is enabled, it will not be
inadvertently turned off unless the bias voltage drops
substantially.
Soft Start and Power Good
Once the POR state is released, the soft start cycle
begins. A 20uA current source charges the capacitor, CSS,
which is connected between SS pin and GND to set the
soft start time. Figure 1 shows the power on sequence.
RT8807/A
VCC
SS
VOUT
PGOOD
VVCCTH ˜ 7.5V
72.5% of VOUT
Figure 1. Power on Sequence
During the soft start, the voltage on SS pin gradually
increases, and the output voltage of the error amplifier is
clamped to prevent the inrush current from the input
capacitors. Once the output voltage exceeds the power
good threshold level (72.5% of output voltage), REFOUT/
PGOOD pin will drive and maintain an reference voltage
1.15V unless VCC falls below POR threshold or Under
Voltage occurs.
Internal/External Reference
The RT8807/A supports the selectable internal/external
reference voltage to provide more flexibility in practical
applications. The selection of the internal/external
reference is described in detail as follows.
a. Using Internal Reference
The internal reference voltage of the RT8807/A is set at
0.6V. When using the internal reference, REFIN/EN pin
should be connected to 5VCC. REFIN/EN pin is also used
for the enable function, the RT8807/A will not be enabled
at start up if the voltage at the REFIN/EN pin is lower than
VENTH.
b. Using External Reference
To use the external reference, the applied voltage on
REFIN/EN pin should be within the tracking range (typically
between 0.45V to 2.5V). This externally input voltage is
used as the reference voltage for the error amplifier.
Therefore, the RT8807/A operates in the tracking mode
because the feedback voltage continuously tracks the
external reference voltage.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS8807/A-02 May 2014
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet RT8807A.PDF ] | |
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