ncp5395t ON Semiconductor, ncp5395t Datasheet - Page 21

• Manufacturer Part Number: ncp5395t
• Description: 2/3/4-phase Controller With On Board Gate Drivers For Cpu Applications
• Manufacturer: ON Semiconductor

General
controller is specifically designed with the necessary
features for a high current CPU system. The IC consists of
the following blocks: Precision Flexible DAC, Differential
Remote Voltage Sense Amplifier, High Performance
Voltage Error Amplifier, Differential Current Feedback
Amplifiers, Precision Oscillator and Saw−tooth Generator,
and PWM Comparators with Hysteresis. The controller also
supports power saving mode as per Intel VR11.1 by
accurately monitoring the current and switching between
multi−phase and single phase operations as requested by the
microprocessor system. Protection features include:
Undervoltage Lockout, Soft−Start, Overcurrent Protection,
Overvoltage Protection, and Power Good Monitor.
Precision Programmable DAC
conform to 2 different specifications: AMD or VR11.1. The
VID7/AMD pin is provided to determine which DAC
specification will be used and which soft−start mode the part
will use for power up. There are two soft−start modes. If
VID7/AMD is above it’s threshold the device will soft−start
and ramp directly to the DAC code present on the VID
inputs. The following truth table describes the functionality:
VID Inputs
normal operation. In AMD mode the VID capture is enabled
just before soft−start. In VR11 mode the VID capture is
enabled at the end of the V
is valid the DAC will track to it. If an invalid VID occurs it
will be ignored for 10 ms before the controller shuts down.
Remote Sense Amplifier
accurately sense the output voltage of the regulator. The
non−inverting input should be connected to the regulator’s
output voltage. The inverting input should be connected to
the return line of the regulator. Both connection points are
intended to be at a remote point so that the most accurate
reading of the output voltage can be obtained. The amplifier
is configured in a very unique way. First, the gain of the
amplifier is internally set to unity. Second, both the inverting
and non−inverting inputs of the amplifier are summing
nodes. The inverting input sums the output voltage return
voltage with the DAC voltage. The non−inverting input
VID7/AMD Pin
The NCP5395T dual edge modulated multiphase PWM
A precision flexible DAC is provided. The DAC will
VID0−VID7 control the target regulation voltage during
A high performance differential amplifier is provided to
Above AMD
Below AMD
Threshold
Threshold
Not active
Active
VID7
BOOT
Thresholds
Thresholds
waiting period. If the VID
Enable Pin
VR11.1
Mode
AMD
FUNCTIONAL DESCRIPTIONS
Soft−Start
Ramp to
Ramp to
Mode
Vboot
VID
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sums the remote output voltage with a 1.3 V reference. The
resulting voltage at the output of the remote sense amplifier is:
circuit and into the inverting input of the error amplifier. The
non−inverting input of the error amplifier is also connected
to the 1.3 V reference. The 1.3 V reference then is subtracted
out and the error signal at the comp pin of the error amplifier
is as normally expected:
pulled low through a small current sink during a fault condition
to prevent accidental charging of the regulator output.
2/3/4 Phase Operation
2− or 3−phase mode, the internal drivers will be used. In
4−phase mode, an external driver must be used to drive
phase 4. The NCP5359 driver is suggested to be used with
the controller. The input to G4 pin will decide which phase
mode the system is in operation. Please refer to the
Application Schematics for more information.
High Performance Voltage Error Amplifier
The error amplifier’s inverting input is VFB and its output
is
compensate the system. This involves a 3 pole, 2 zero
compensation network. The comp pin is pulled to ground
before soft−start for smooth start up.
Differential Current Sense
output current of each phase. These current sense amplifiers
sense the current through the corresponding phase. A
voltage is generated across a current sense element such as
an inductor or sense resistor. The sense element should be
between 0.3 mW and 1.5 mW. It is possible to sense both
negative and positive going current. The information is used
to create the signal CSSUM and provide feedback for
current sharing.
Precision Oscillator
oscillator is programmed by the summed resistance of an
oscillator resistor and a current limit resistor. The output
voltage of this pin is 2V used as the reference for the current
limit. The oscillator frequency range is 125 KHz/phase to
1000 KHz/phase. The oscillator frequency is proportional to
the current drawn out of the OSC pin. Connecting a resistor
(R
oscillator frequency. The relation between the R
can be described as below:
This signal then goes through a standard compensation
The non−inverting input of the remote sense amplifier is
The part can be configured to 2−, 3−, or 4−phase mode. In
A high performance voltage error amplifier is provided.
Four differential amplifiers are provided to sense the
A programmable precision oscillator is provided. This
COMP.
osc
) from OSC pin to the ground will set the target
V
Diffout
A standard type 3 compensation circuit is used
+ V
V
out
comp
) 1.3 V * V
+ V
dac
* V
dac
out
* V
outreturn
osc
and F
sw