RT9911PQV RICHTEK [Richtek Technology Corporation], RT9911PQV Datasheet - Page 28

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

RT9911
The input parameters for CH4 asyn-boost in DCM
compensation are as follows :
The results we will get for CH4 asyn-boost in DCM
compensation are as follows :
The major steps for getting above results :
1.
2. Select suitable inductor to ensure I
3. Set f
For example:
4.
5.
www.richtek.com
28
R1, the voltage divider resistor in between V
FB.
V
V
I
f
L, inductance
C
on ceramic output capacitor.
R
(ceramic output capacitor)
R2, the voltage divider resistor in between FB and ground.
C
R
C
connect to ground
C
ignored if C
OUT(MAX.)
OSC
DCM, which is let inductor current falls to zero on each
switch cycle.
R2 =
L <
Find
Get
where
IN
OUT
OUT
ESR
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.
, operating frequency
2
, desired output voltage
, output capacitance. This compensation is based
, ESR (Equivalent Series Resistance) of C
R
C
the
R1
I x
V
C
sufficient below f
M
IN
=
OUT(MAX.)
, maximum output load
x
load
=
x
GM
V
P
f
f
D
V
C
f
LP
OUT
C
< 10pF)
V
OUT
=
pole
x
V
IN
x
x V
(1
FB
f
G
-
OSC
10
f x
,
V
-
dod
R
P
f :
D)
FB
OSC
LOAD
LP
or
,
where
=
lower
OSC
2
=
π
I
.
OUT(MAX.)
x
V
G
(M
OUT
dod
-
1)
=
2
2
x
x
.
OUT(MIN.)
x
M
R
V
LOAD
1 -
OUT
D
x
x
works in
OUT
C
2
OUT
C
M
x
and
and
OUT
M
1 -
,
1 -
,
6.
7. Find ffz, zero and ffp, pole ratio of voltage divider with
8. Get C
9. Evaluate C
Asyn-boost in CCM :
We call it CCM because inductor current is always
continuous in operation. The benefit of designing in CCM
is lower V
efficiency from the lower coil loss, but with the expense
of larger inductor size and cost and the control loop comes
with a RHPZ (Right Hand Plan Zero) and a conjugate double
pole in the frequency domain to worry about.
The fixed parameters for CH4 asyn-boost in CCM
compensation are as follows :
The input parameters for CH4 asyn-boost in CCM
compensation are as follows:
Transconductance (from FB to COMP), GM = 200us
Internal voltage ramp to decide duty cycle, V
Feedback voltage, V
R1, the voltage divider resistor in between V
FB.
V
V
I
I
f
which is duty to V
C
(ceramic output capacitor).
OUT(MAX.)
OUT(MIN.)
OSC
D
Get
by
ratio
C
C
IN
OUT
F
F
P
=
.
, input voltage.
letting
, operating frequency
=
=
duty
, desired output voltage
C
=
C
F
2
C
OUT
π
ffp
ffz
by placing ffp on f
=
, minimum output laod
OUT
, maximum output load
×
cycle
C
comp
ff
=
x
1
OUT
P
Z
. C
V
and inductor current ripple and higher
R
V
×
R
OUT
ESR
=
FB
R1
x
P
C
zero
- 1
R
is for canceling the zero from C
OUT
,
.
where
LOAD
R
V
C
V
FB
C
OUT
=
P
transfer function.
IN
load
can
= FB = 1V
C
ff
be
Z
and ffz therefore on
pole.
=
DS9911-04 August 2007
ignore
ratio
f
C
.
if
C
P
<
10pF.
P
OUT
= 1V
ratio
f
C
and
OUT
.