RT8113 RICHTEK [Richtek Technology Corporation], RT8113 Datasheet - Page 12

• Manufacturer Part Number: RT8113
• Description: Single Phase VR11.1 PWM Controller with 7-bit VID
• Manufacturer: RICHTEK [Richtek Technology Corporation]

VCC12
RT8113
www.richtek.com
12
Applications Information
The RT8113 is a single-phase synchronous buck DC/DC
converter with embedded MOSFET driver. The internal
VID DAC is designed to interface with the Intel 7-bit
VR11.X compatible VID table for Ibexpeak platform CPU’s
AXG VR application.
Supply voltage, VCC5 regulation and POR
There are two supply voltage pins built-in in the RT8113,
VCC12 and VCC5. VCC12 is a power input pin which
receives external 12V voltage for embedded driver logic
operation. VCC5 is a power output pin which is the output
of an internal 5V LDO regulator. The mentioned 5V LDO
regulator regulates VCC12 to generate a 5V voltage
source for internal gate logic and external circuit biasing,
e.g., OCP biasing. Since the VCC5 voltage is regulated,
the variation of VCC5 (2%) will be much smaller than
Platform ATX +5V (5%~7%). The maximum supply current
of VCC5 is 10mA, which is designed only for controller
circuit biasing. The recommended configuration of the
RT8113 supply voltages is as follows: Platform ATX +12V
to the VCC12 pin, and decoupling capacitors on the
VCC12 and VCC5 pins (minimum 0.1μF).
The initialization of the RT8113 requires both the voltage
on the VCC12 and VCC5 to be ready. Since VCC5 is
regulated internally from VCC12, the VCC5 voltage will
be ready (>4.6V) after VCC12 reaches about 7V, so there
is no power sequence problem between VCC12 and
VCC5. After VCC5 > 4.6V and VCC12 > 9.6V, the internal
power-on-reset (POR) signal goes high. This POR signal
indicates the power supply voltages are all ready and
initiates soft-start sequence. When POR = low, The
RT8113 will try to turn off both high-side and low-side
MOSFETs to prevent catastrophic failure.
VCC5
Figure 1. Circuit for Power Ready Detection
9.6V
4.6V
CMP
CMP
+
-
+
-
POR
POR : Power ON Reset
Switching Frequency
The switching frequency of the RT8113 is set by an external
resistor connected from the RT/EN pin either to GND or to
VCC5. If the resistor is connected from RT/EN to GND,
the load line function will be enabled as well. More details
will be described in the Load Line section. The frequency
follows the graph in Figure 2.
Chip Enable
The enable function of the RT8113 is combined in the
RT/EN pin. Besides frequency setting function, pulling the
RT/EN pin to GND can also force the RT8113 to enter soft
shutdown sequence. It is recommended to connect a
control switch from the RT/EN pin to GND in parallel with
RT setting resistors. The RT8113 will enter soft shutdown
sequence when the control switch is turned on.
Soft-Start
The V
the SS pin to FBRTN. Before power on reset (POR =
low), the SS pin is held at GND. After power on reset
(POR = high) and an extra delay of 1600μs (t
controller initiates ramping up. V
during normal operation of the RT8113, where V
positive input of compensation error amplifier, which can
be described as V
will be described later in the Load Line section). The first
ramping up duration of V
Figure 2. Switching Frequency vs. R
1000
800
600
400
200
OUT
0
0
soft-start slew rate is set by a capacitor from
10
EAP
20
= V
DAC
30
OUT
− V
R
(t
40
RT
D2
ADJ
OUT
) ramps V
(kΩ)
DS8113-02 April 2011
(The definition of V
will always trace V
50
RT
60
Resistance
OUT
to V
70
EAP
D1
), the
is the
BOOT
80
EAP
ADJ
.