RT9911PQV RICHTEK [Richtek Technology Corporation], RT9911PQV Datasheet - Page 30

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

RT9911
The input parameters for CH5 asyn-inverter in DCM
compensation are as follows :
The results we will get for CH5 asyn-inverter 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.
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30
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 V
C
R
C
connect to ground
C
ignored if C
R2
OUT(MAX.)
OSC
then
DCM, which is let inductor current falls to zero on each
switch cycle.
L <
Find
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
C
R2
R1
the
I x
sufficient below f
R
V
OUT(MAX.)
x
, maximum output load
=
load
LOAD
IN
1M
V
V
P
f
x
FB
REF
C
< 10pF)
(1
pole
x
=
=
−
0
-
I
-
f
V
OUT(MAX.)
OSC
10
D)
- 1
f x
V
-
OUT
V
f :
(-8)
FB
0
OUT
OSC
LP
or
If .
=
=
OSC
lower
R1
125k
2
.
π
=
x
1M
R
Ω
LOAD
Ω
2
and
x
OUT(MIN.)
C
V
OUT
OUT
,
=
works in
OUT
(-8)V
C
REF
and
and
OUT
.
5.
6.
7. Find ffz, zero and ffp, pole ratio of voltage divider with
8. Get C
9. Evaluate C
Asyn-Inverter 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 CH5 asyn-inverter in CCM
compensation are as follows :
The input parameters for CH5 asyn-inverter in CCM
compensation are as follows :
Transconductance (from FB to COMP), GM = 200us
Internal voltage ramp to decide duty cycle, V
Feedback voltage, V
Reference voltage, V
R1, the voltage divider resistor in between V
FB.
V
V
I
D
Get
Get
by
ratio
C
C
which is duty to Vout transfer function.
C
(ceramic output capacitor).
OUT(MAX.)
IN
OUT
F
P
F
=
.
, input voltage.
letting
=
=
duty
R
C
, desired output voltage
=
C
2
C
C
F
π
OUT
ffp
ffz
=
=
by placing ffp on f
×
OUT
, maximum output load
cycle
GM
C
comp
ff
=
x
f
1
OUT
f
LP
Z
P
C
abs(V
R
. C
and inductor current ripple and higher
×
x
R
ESR
x V
=
R1
x
G
C
zero
P
V
R
dod
P
,
is for canceling the zero from C
IN
.
OUT
R
V
where
LOAD
abs(V
C
+
REF
C
,
FB
=
P
REF
where
)
abs(V
load
can
+
= FB = 0V
= 1V
V
OUT
ff
C
REF
be
Z
pole.
and ffz therefore on
OUT
G
)
=
DS9911-04 August 2007
ignore
dod
ratio
)
f
C
.
=
V
.
if
OUT
D
C
P
,
<
10pF.
P
OUT
= 1V
ratio
f
C
and
OUT
.