RT8113 RICHTEK [Richtek Technology Corporation], RT8113 Datasheet - Page 17

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

Load Line
The RT8113 utilizes inductor DCR current sense technique
for load line control function. The sensed inductor current
I
0.5 x I
ADJ pin is established. The V
and subtracted by V
PTC (Positive Temperature Coefficient) current, an NTC
(Negative Temperature Coefficient) resistor is needed to
connect ADJ pin to GND. If the NTC resistor is properly
selected to compensate the temperature coefficient of I
the voltage on ADJ pin will be proportional to I
temperature effect. In the RT8113, the positive input of
error amplifier is “V
“V
decreases linearly with I
defined as :
Basically, the resistance of R
the load line. The temperature coefficient of R
compensates the temperature effect of the load line.
The load line function of the RT8113 can be disabled by
connecting the RT/EN pin resistor to VCC5 instead of
GND. When the RT/EN pin resistor is connected to VCC5,
the current-sense circuit works normally while V
longer contains droop, and the reference voltage of the
error amplifier will remain equal to V
current. The running frequency of the RT8113 will always
be the same whether connecting RT/EN to VCC5 or GND.
Over Current Protection (OCP)
In Figure 8, V
the RT8113, V
compensated. Once V
triggered and latched. The OCP function will not be
influenced by enabling or disabling load line since the
voltage on the ADJ pin always contains real-time
information of load current. Once OCP is triggered, the
RT8113 will turn off both high-side MOSFETs and low side
MOSFETs.
DS8113-02 April 2011
LL(Load Line) =
Δ
X
V
is multiplied by 0.5 and sent to ADJ pin. After the current
DAC
ADJ
X
− 0.1 x V
=
injects into the ADJ resistors, the voltage of the
2
1
x I x R
OCSET
X
ADJ
ADJ
Δ
is proportional to I
Δ
V
DAC
I
DAC
is equal to VCC x R2/(R1 + R2). For
”. Thus, the output voltage which
ADJ
OUT
OUT
ADJ
− 0.1 x V
to generate V
OUT
=
is larger than V
10
is obtained. The load line is
1
ADJ
ADJ
ADJ
x
is then multiplied by 0.1
DAC
sets the resistance of
Δ
Δ
” and V
V
I
OUT
OUT
EAP
ADJ
regardless of output
. Because I
and is thermally
=
OCSET
OUT
DCR x R
OUT
20 x R
will follow
, OCP is
without
EAP
X
CSN
is a
ADJ
ADJ
no
X
,
Over Voltage Protection (OVP)
The over-voltage protection monitors the output voltage
via the FB pin. Once V
is triggered and latched. The RT8113 will turn on low-side
MOSFET and turn off high side MOSFET to protect CPU.
A 20μs delay is used in OVP detection circuit to prevent
false trigger.
Over Temperature Protection (OTP)
The over-temperature protection function of the RT8113 is
built inside the controller to prevent overheat damage. OTP
occurs when the die temperature of the RT8113 exceeds
160°C, in which the RT8113 then turns off both high-side
MOSFETs and low side MOSFETs.
Loop Compensation
The RT8113 is a voltage mode controller and requires
external compensation. To compensate a typical voltage
mode buck converter, there are two ordinary compensation
schemes, commonly known as type-II compensator and
type-III compensator. The choice of using type-II or type-
III compensator lies with the platform designers, and the
main concern deals with the position of the capacitor ESR
zero and mid-frequency to high-frequency gain boost.
Typically, the ESR zero of output capacitor will tend to
stabilize the effect of output LC double poles. Hence, the
position of the output capacitor ESR zero in frequency
domain may influence the design of voltage loop
compensation. Figure 9 shows a typical control loop using
type-III compensator. Below is the compensator design
procedure.
VCC5 or
VCC12
R2
R1
Figure 8. Over Current Protection
OCSET
FB
ADJ
exceeds“V
+
CMP
-
EAP
RT8113
+ 150mV”, OVP
www.richtek.com
OCP
17