RT9911PQV RICHTEK [Richtek Technology Corporation], RT9911PQV Datasheet - Page 27

• Manufacturer Part Number: RT9911PQV
• Description: 6 Channel DC/DC Converters
• Manufacturer: RICHTEK [Richtek Technology Corporation]

CH3 Syn Boost Controller with External MOSFET :
CH3 boost controller driving external logic level MOSFET
employs current-mode control to simplify the control loop
compensation. There is a RHPZ (Right Hand Plan Zero)
appeared in the loop-gain frequency response when a
boost converter operates with continuous inductor current
(typically the case), we also call it works in CCM
(Continuous Current Mode). For stability, cross over
frequency (f
RHPZ frequency.
The fixed parameters for CH3 boost compensation are as
follows :
The input parameters for boost compensation are as
follows :
The results we will get for boost compensation are as
follows :
DS9911-04 August 2007
Transconductance (from FB to COMP), GM = 200us
Feedback voltage, V
R
transresistance, R
R1, the voltage divider resistor in between V
FB.
V
V
I
F
L, inductance
R
(ceramic output capacitor)
T
R
R2, the voltage divider resistor in between FB and ground.
C
R
C
connect to ground
C
ignored if C
OUT(MAX.)
OSC
DRP
IN
OUT
DS(ON)
ESR
CS
F
C
P
C
, feedforward capacitor in parallel with R1.
, connect in between COMP pin and ground. (Can be
, compensation resistor on COMP pin.
, compensation capacitor in series with R
, input voltage.
, the transresistance of current sense.
(%), Transient droop.
, desired output voltage
, operating frequency
, ESR (Equivalent Series Resistance) of C
, the NMOSFET R
, maximum output load
C
), unity gain frequency, must lower than this
P
< 10pF)
CS
.
FB
= FB = 0.8V
DS(ON)
, which is use to find
OUT
C
and
and
OUT
The major steps for getting above results :
1. R
The rest of the steps are the same as sync-boost.
CH4 Asyn-Boost Controller with External MOSFET
CH4 is an asyn-boost controller driving external logic level
N type MOSFET, which employs voltage mode control to
regulate the output voltage. Compensation depends on
designing the loading range working in discontinuous or
continuous inductor current mode. (DCM or CCM).
Asyn-Boost in DCM :
We call it DCM because inductor current falls to zero on
each switch cycle. The benefit of designing in DCM is the
simple loop compensation, which has no RHPZ (Right
Hand Plan Zero) and conjugate double pole in the frequency
domain to worry about, but has a single load pole instead.
However, the output ripple and efficiency are worse than
in CCM (Continuous Inductor Current). If the loading is
around tens of mA, it is not bad to design in DCM with
less impact on the output ripple and efficiency, but gain
more easy to stabilize the control loop.
The fixed parameters for CH4 asyn-boost in DCM
compensation are as follows:
COMP
C
on ceramic output capacitor.
Transconductance (from FB to COMP), GM = 200us.
Internal voltage ramp to decide duty cycle, V
Feedback voltage, V
OUT
CS
, output capacitance. This compensation is based
= 2 x R
C
P
DS(ON)
R
C
C
C
GM
+
-
FB
FB
Figure 9
1V
= FB = 1V
V
OUT
R1
R2
C
F
RT9911
www.richtek.com
R
C
ESR
OUT
P
= 1V.
I
OUT
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