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PDF RT9258 Data sheet ( Hoja de datos )
| Número de pieza | RT9258 | |
| Descripción | Two Phases Synchronous Buck PWM Controller | |
| Fabricantes | Richtek Technology | |
| Logotipo |  |
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RT9258
Two Phases Synchronous Buck PWM Controller
General Description
The RT9258 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 a WQFN-24L 4x4 package.
The inductor currents are sensed by lossless DCR current
sensing technique for current balance and over current
protection. The RT9258 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.
Applications
z Middle to High End GPU Core Power
z High End Desktop PC Memory Core Power
z Low Voltage, High Current DC / DC Converter
z Voltage Regulator Modules
Ordering Information
RT9258
Package Type
QW : WQFN-24L 4x4 (W-Type)
Note :
Lead Plating System
G : Green (Halogen Free and Pb Free)
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
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Features
z Two-Phase Power Conversion with Single 12V
Power Supply
z Embedded 5V Upper Gate Driver and 12V Lower
Gate Driver
z Internal Regulated 5V Output
z Precise Core Voltage Regulation
z Selectable Internal / External Reference
z Differential Inductor DCR Current Sense
z External Programmable Voltage Droop Control
z Enable Control for External Shutdown
z Adjustable Operating Frequency
z Adjustable Soft Start
z Power Good and Output Current Indication
z Adjustable Over Current Protection
z Over Voltage Protection
z Under Voltage Protection
z Over Temperature Protection
z RoHS Compliant and Halogen Free
Pin Configurations
(TOP VIEW)
24 23 22 21 20 19
PHASE2 1
18 COMP
LGATE2
DROOP
VCC
2
3
4
PGND
17 RT
16 IOUT/IMAX
15 CSP2
LGATE1 5
PHASE1 6
14 CSN2
25 13 CSN1
7 8 9 10 11 12
WQFN-24L 4x4
DS9258-01 April 2011
www.richtek.com
1
1 page  
Functional Pin Description
PHASE2 (Pin 1), PHASE1 (Pin 6)
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.
LGATE2 (Pin 2), LGATE1 (Pin 5)
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 3)
Set the load line for droop control. Connect this pin with a
resistor to ground.
VCC (Pin 4)
Provide a 12V supply voltage for the IC. Connect a
10Ω/1uF low pass filter to sustain high PSRR.
UGATE1 (Pin 7), UGATE2 (Pin 24)
Upper Gate Drivers. Theses pins provide the gate drive for
the converter's high-side MOSFET. Connect these pins
to the high-side MOSFET gate.
BOOT1 (Pin 8), BOOT2 (Pin 23)
Bootstrap Power Pins. Theses pins power the high-side
MOSFET drivers.
5VCC (Pin 9)
Internal Regulator Power Pin. The regulated voltage
provides power supply for all low-voltage circuits. Bypass
at least 1uF ceramic capacitor to sustain high PSRR.
AGND (Pin 10)
Signal ground for the IC. All voltage levels are measured
with respect to this pin.
EN2B (Pin 11)
EXT_12V Detection Pin. RT9258 latches high/low status
of this pin in soft start period. If the result is low, RT9258
will enter two phase operation. If it's high, RT9258 turns
off phase2 and operate in single phase only.
CSP1 (Pin 12), CSP2 (Pin 15)
These pins are positive input of current sensing
transconductance amplifiers 1 and 2.
DS9258-01 April 2011
RT9258
CSN1 (Pin 13), CSN2 (Pin 14)
These pins are negative input of current sensing
transconductance amplifiers 1 and 2.
IOUT/IMAX (Pin 16)
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 (Pin 17)
Frequency Timing Resistor. Connect a resistor from RT
to AGND to set the clock frequency.
COMP (Pin 18)
Compensation Pin. This pin is the output of the error amplifier.
FB (Pin 19)
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 20)
Soft-Start Pin. Connect a capacitor from this pin to ground
to set the soft-start interval.
REFIN/EN (Pin 21)
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 22)
Reference Out and Power GOOD. This pin drives 1.15V
out once FB exceeds 75% of the reference voltage after
soft- start ends. This pin keeps at this voltage regardless
of internal or external reference is used.
PGND [Exposed Pad (25)]
Power ground pin. Tie the synchronous PWM converter's
low-side MOSFET source to this pin.
www.richtek.com
5
5 Page 
Application Information
The RT9258 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 RT9258 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 RT9258 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.
RT9258
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 RT9258 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 RT9258 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 RT9258 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 and 2.5V). This externally input voltage is
used as the reference voltage for the error amplifier.
Therefore, the RT9258 operates in the tracking mode
because the feedback voltage continuously tracks the
external reference voltage.
DS9258-01 April 2011
www.richtek.com
11
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet RT9258.PDF ] | |
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