rt9241 ETC-unknow, rt9241 Datasheet - Page 9

• Manufacturer Part Number: rt9241
• Description: Two-phase Dc/dc Controller For Cpu Core Power Supply
• Manufacturer: ETC-unknow

Operation
RT9241 is a two-phase DC/DC controller that
precisely regulates CPU core voltage and balances
the current of different power channels. The
converter consists of RT9241 and its companion
MOSFET driver provide high quality CPU power and
all protection function to meet the requirement of
modern VRM.
Voltage control
The reference of V
VRM9.0 specification. Control loop consists of error
amplifier, two-phase pulse width modulator, driver
and power components. Like conventional voltage
mode PWM controller, the output voltage is locked at
the VREF of error amplifier and the error signal is
used as the control signal VC of pulse width
modulator. The PWM signals of different channels
are generated by comparison of EA output and spilt-
phase saw-tooth wave. Power stage transforms V
to output by PWM signal on-time ratio.
Current balance
RT9241 senses the current of low side MOSFET in
each synchronous rectifier when it is conducting for
channel current balance and droop tuning. The
differential sensing GM amplifier converts the voltage
on the sense component (can be a sense resistor or
the R
signal into internal balance circuit. The current
balance circuit sums and averages the current
signals then produces the balancing signals injected
to pulse width modulator. If the current of some
power channel is greater than average, the balancing
signal reduces the output pulse width to keep the
balance.
Load Droop
The sensed power channel current signals regulate
the reference of DAC to form a output voltage droop
proportional to the load current. The droop or so call
“active voltage positioning” can reduce the output
voltage ripple at load transient and the LC filter size.
DS9241-00 November 2001
DS(ON)
of the low side MOSFET) to current
CORE
is provided by a 5-bit DAC of
Preliminary
IN
To Current Balance
To Current Balance
To Droop Tune
To Droop Tune
To Over Current Detection
To Over Current Detection
Fault detection
The chip detects V
good detection. The “hiccup mode” operation of over
current protection is adopted to reduce the short
circuit current. The in-rush current at the start up is
suppressed by the soft start circuit through clamping
the pulse width and output voltage.
Application Circuit setting
MOSFET driver detection and converter start up
RT9241 interface with companion MOSFET driver
(like RT9600 or HIP660X series) for correct converter
initialization. The tri-phase PWM output (high, low,
high impedance) pins sense the interface voltage at
IC POR acts (both VDD and DVD trip). The channel
is enabled if the pin voltage is 1.2V less than VDD.
Please tie the both PWM output to driver input for
correct converter start-up.
Current sensing setting
RT9241 senses the current of low side MOSFET in
each synchronous rectifier when it is conducting for
channel current balance and droop tuning. The
differential sensing GM amplifier converts the voltage
on the sense component (can be a sense resistor or
the R
signal into internal circuit (see Fig.1).
DS(ON)
2/3 I
2/3 I
2/3 I
2/3 I
2/3 I
2/3 I
Sample & Hold
Sample & Hold
X
X
X
X
X
X
Fig.1 Current Sense Circuit
of the low side MOSFET) to current
CORE
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I
for over voltage and power
X
X
GM
GM
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RT9241
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