rt9246 Richtek Technology Corporation, rt9246 Datasheet - Page 14

• Manufacturer Part Number: rt9246
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

RT9246
Design Example
Given:
www.richtek.com
14
1. Compensation Setting
b. EA Compensation Network :
Apply for three phase converter
a. Modulator Gain, Pole and Zero :
OCP trip point set at 30A for each channel (S/H)
R
C
V
I
V
V
L = 2μH
LOAD
IN
DROOP
Modulator Gain =
where V
CORE
DS(ON)
OUT
The asymptotic bode plot of EA compensation and
C2 = 33pF and use the type 2 compensation
Middle Band Gain =
PWM loop gain is shown as Figure 6.
From the following formula :
scheme shown in Figure 5.
COMP
LC Filter Pole =
ESR Zero =
Select R1 = 2.4kΩ, R2 = 24kΩ, C1 = 6.6nF,
From the following formulas :
F
Middle Band Gain is 10 (i.e 20dB).
By calculation, the F
= 12V
Z
= 9,000μF with 2mΩ ESR.
(max) = 60A
=
= 1.5V
= 6mΩ of low side MOSFET at 27°C
= 120mV at full load
2
RAMP
π
x
C2
R
1
: ramp amplitude of sawtooth wave
DACOUT
2π x ESR x C
-
+
2
C1
x
C
2
V
π
Figure 5.
V
1
RAMP
,
IN
x
R
1
R
Z
1
F
FB
2
1
= 1kHz, F
P
LC
=
R3,C3 are used in type
3 compensation scheme
(left NC in type 2)
=
OUT
1.9V
12V
2
= 1.2kHz and
π
×
= 8.8kHz
3
2
x
P
= 4.2 (12.46dB)
R
C3
= 200kHz and
2
x
1
⎛
⎜
⎝
C
C
1
1
×
+
C
C
VDIF
2
2
⎞
⎟
⎠
3. Over-Current Protection Setting
2. Droop & DAC Offset Setting
4. Soft-Start Capacitor Selection
C
SS
I
The suggested I
R
V
therefore R
The R
When the low side MOSFET working at 70°C and
5000ppm/°C temperature coefficient of R
R
6mΩ × {1+ (70°C − 27°C) × 5000ppm/°C} = 7.3mΩ.
R
R
OCP trip point set at 30A for each channel,
Take the temperature rise into account, the R
70°C will be :
R
For each channel the load current is 60A / 3 = 20A
and the ripple current, ΔI
X
The load current, I
Using the following formula to select the appropriate
I
= 0.1μF is the suitable value for most application.
X (MAX)
DROOP
SP
DS(ON)
ADJ
ADJ_27°C
IMAX_27°C
=
100
-20
-40
-60
80
60
40
20
R
= R
0
5us
Asymptotic Bode Plot of PWM Loop Gain
10
at 70°C is given as :
10
DS(ON)
DS(ON)
SN
at 70°C is given as :
= 120mV = 45.9μA × 2 × 3 (phase no.) × R
for the S/H of GM amplifier :
R
x
I
× (R
= 2.4kΩ, then I
X
SP
× (R
×
100
1.5V
ADJ
(MAX)
100
2uH
30A
of MOSFET varies with temperature rise.
DS(ON)_27°C
will be 435Ω.
DS(ON)_27°C
X
=
x
1000
is in the order of 40 to 50μA, select
=
1K
R
⎛
⎜
⎝
L
1.4
, at S/H is
Figure 6.
1
DS(ON)
Frequency (Hz)
−
×
10000
1.5V
10K
12V
/ R
L
X (MAX)
0.6V
R
/ R
, is given as :
R
IMAX
Modulator Gain
×
DS(ON)_70°C
DS(ON)_70°C
SP
PWM Loop Gain
DS9246-06 March 2007
18.36A
Uncompensated EA Gain
20
100000
⎞
⎟
⎠
Compensated EA Gain
100K
will be 45.9μA.
, R
A
=
−
IMAX
3.28A
1000000 10000000
Δ
1M
2
) = 358Ω
I
) = 9.2kΩ
L
= 11.2kΩ
=
18
DS(ON)
10M
.
36
IMAX
A
, the
ADJ
at
.
,