rt9244 Richtek Technology Corporation, rt9244 Datasheet - Page 9

• Manufacturer Part Number: rt9244
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

Application Information
RT9244 is a multi-phase DC/DC controller that precisely
regulates CPU core voltage and balances the current of
different power channels. The converter consisting of
RT9244 and its companion MOSFET driver provides high
quality CPU power and all protection functions to meet
the requirement of modern VRM.
Voltage Control
RT9244 senses the CPU V
amplifier to minimize the voltage drop on PCB trace at
heavy load. VSEN & SGND are the differential inputs. VDIF
is the output node of the differential voltage & the input for
PGOOD & OVP sense. The internal high accuracy V
DAC provides the reference voltage for K8 compliance.
Control loop consists of error amplifier, multi-phase pulse
width modulator, driver and power components. Like
conventional voltage mode PWM controller, the output
voltage is locked at the V
signal is used as the control signal V
modulator. The PWM signals of different channels are
generated by comparison of EA output and split-phase saw-
tooth wave. Power stage transforms V
signal on-time ratio.
Current Balance
RT9244 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
MOSFET) to current signal into internal balance circuit.
The current balance circuit sums and averages the current
signals and 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-called “active voltage
positioning” can reduce the output voltage ripple at load
transient and the LC filter size.
DS9244-06 March 2007
REF
CORE
of error amplifier and the error
by an precise instrumental
DS(ON)
IN
to output by PWM
C
of the low side
of pulse width
ID
Fault Detection
The chip detects V
detection. The “hiccup mode” operation of over-current
protection is adopted to reduce the short circuit current.
The inrush current at the start up is suppressed by the
soft start circuit through clamping the pulse width and output
voltage.
Phase Setting and Converter Start Up
RT9244 interfaces with companion MOSFET drivers (like
RT9600, RT9602 series) for correct converter initialization.
The tri-state PWM output (high, low and high impedance)
pins sense the interface voltage at IC POR period (both
V
is 1.2V less than V
and the current sense pins to GND or left floating if the
channel is unused. For 3-Channel application, connect
PWM4 high.
Current Sensing Setting
RT9244 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
MOSFET) to current signal into internal circuit (see
Figure 1).
<
<
<
CC
Over-Current
Detection
Current
Balance
Droop Tune
and DVD trip). The channel is enabled if the pin voltage
Sample & Hold
Figure 1. Current Sense Circuit
CORE
CC
. Please tie the PWM output to V
for over voltage and power good
I
X
GM
-
+
I
I
BP
BN
DS(ON)
ISPx
ISNx
RT9244
www.richtek.com
of the low side
R
R
SN1
SP1
R
S
I
L
CC
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