RT8876A
Application Information
The RT8876A is a CPU power controller which includes
two channels : a 3/2/1 phase synchronous Buck controller
with three integrated drivers for CORE VR, and a single
phase Buck controller for AXG VR. The RT8876A is
compliant with Intel VR12/IMVP7 voltage regulator
specification to fulfill Intel's CPU power supply
requirements of both CORE andAXGvoltage regulators.
ASerial VID(SVID) interface is built-in in the RT8876Ato
communicate with Intel VR12/IMVP7 compliant CPU. The
RT8876A adopts G-NAVPTM (Green Native Adaptive
Voltage Positioning), which is Richtek's proprietary
topology derived from finite DC gain EA amplifier with
current mode control, making it an easy setting PWM
controller, meeting all Intel CPU requirements ofAVP. The
load line can be easily programmed by setting the DC
gain of the error amplifier. The RT8876Ahas fast transient
response because of theG-NAVPTM commanding variable
switching frequency. Based on the G-NAVPTM topology,
the RT8876Aalso features a quick response mechanism
so that fully phases can respond for optimized AVP
performance during load transient. TheG-NAVPTM topology
also represents a high efficiency system with green power
concept. With the G-NAVPTM topology, the RT8876A is
also a green power controller with high efficiency under
heavy load, light load, and very light load conditions. The
RT8876A supports mode transition function with various
operating states, including multi-phase, single phase and
DEM (Diode Emulation Modes). These different operating
states allow the overall power control system to have the
lowest power loss. By utilizing the G-NAVPTM topology,
the operating frequency of the RT8876A varies with VID,
load, and input voltage to further enhance the efficiency
even in CCM. The built-in high accuracy DAC converts
the SVIDcode ranging from 0.25V to 1.52V with 5mV per
step. The RT8876A supports VID on-the-fly function with
three different slew rates : Fast, Slow and Decay. The
RT8876A also builds in a high accuracy ADC for some
platform setting functions, such as no-load offset or over
current level. The controller supports bothDCR and sense
resistor current sensing. The RT8876A provides power VR
ready signals for both CORE VR and AXG VR. It also
features complete fault protection functions including over
voltage, under voltage, negative voltage, over current and
under voltage lockout. The RT8876A is available in a
WQFN-56L 7x7 small footprint package.
General Loop Functions :
Power Ready (POR) Detection
During start-up, the RT8876A will detect the voltage at
the voltage input pins : VCC5, VCC12 and EN. When
VCC5 > 4.24V and VCC12 > 4V, the RT8876A will
recognize the power state of system to be ready (POR =
high) and wait for enable command at the EN pin. After
POR = high and VEN > 0.7V, the RT8876Awill enter start-
up sequence for both CORE rail andAXGrail. If the voltage
at any voltage pin drops below low threshold (POR = low),
the RT8876Awill enter power down sequence and all the
functions will be disabled. Normally, connecting system
VTT (1.05V) to the EN pin and power stage VIN (12V) to
the VCC12 pin is recommended. 2ms (max) after the chip
has been enabled, the SVIDcircuitry will be ready. All the
protection latches (OVP, OCP, UVP) will be cleared only
after POR = low. The condition of VEN = low will not clear
these latches.
VCC5
+
-
4.24V
1.06V
VCC12
+
-
+
-
POR
4V
EN
+
-
Chip EN
0.7V
+
-
1.06V
Figure 4. Power Ready (POR)Detection
Precise Reference Current Generation
The RT8876Aincludes complicated analog circuits inside
the controller. These analog circuits need very precise
reference voltage/current to drive these analog devices.
The RT8876A will auto generate a 2.14V voltage source
at the IBIAS pin, and a 53.6kΩ resistor is required to be
connected between IBIAS and analog ground. Through
this connection, the RT8876A will generate a 40μA current
from the IBIAS pin to analog ground, and this 40μAcurrent
Copyright 2012 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS8876A-02 October 2012
www.richtek.com
29
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
