rt9246 Richtek Technology Corporation, rt9246 Datasheet - Page 11

• Manufacturer Part Number: rt9246
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

Application Information
RT9246 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
RT9246 and its companion MOSFET driver provides high
quality CPU power and all protection functions to meet
the requirement of modern VRM.
Voltage Control
RT9246 senses the CPU V
amplifier to minimize the voltage drop on PCB trace at
heavy load. VSEN & SGND are the differential inputs. V
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
error 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
sawtooth wave. Power stage transforms V
PWM signal on-time ratio.
Current Balance
RT9246 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 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.
DS9246-06 March 2007
CORE
REF
of error amplifier and the
by an precise instrumental
DS(ON)
C
of the low side
IN
of pulse width
to output by
DIF
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
RT9246 interfaces with companion MOSFET drivers (like
RT9600, RT9602 or RT9603 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
the pin voltage is 1.2V less than V
output to V
floating if the channel is unused. For 2-Channel application,
connect PWM3 high.
Current Sensing Setting
RT9246 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). Be careful to choose GND sense input, ISN, of
the GM amplifier for effective channel current balance.
Current
Balance
Droop Tune
Over-Current
Detection
Current
Balance
Droop Tune
Over-Current
Detection
Current
Balance
Droop Tune
Over-Current
Detection
2I
2I
2I
I
I
I
I
I
I
X
X
X
CC
X
X
X
X
X
X
Figure 1. Current Sense Circuit
Sample
Sample
Sample
CC
and the current sense pins to GND or left
Hold
Hold
Hold
&
&
&
and DVD trip). The channel is enabled if
CORE
I
I
I
X1
X2
X3
for over voltage and power good
GM
GM
GM
-
+
+
-
-
+
I
I
I
I
I
I
BP
BN
BN
BN
BP
BP
CC
ISP1
ISN1
ISP2
ISP3
ISN23
DS(ON)
. Please tie the PWM
Channel 2 & 3
GND return
R
R
R
R
SN1
SP1
SP2
R
SP3
RT9246
SN23
www.richtek.com
of the low side
R
R
S
S
I
I
L
L
R
S
I
L
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