rt9244 Richtek Technology Corporation, rt9244 Datasheet - Page 12

• Manufacturer Part Number: rt9244
• Description: Multi-phase Controller Core Power Supply
• Manufacturer: Richtek Technology Corporation

RT9244
www.richtek.com
12
1. Compensation Setting
Design Example
Given:
b. EA Compensation Network :
a. Modulator Gain, Pole and Zero :
Apply for three phase converter
I
OCP trip point set at 33A for each channel (S/H)
R
C
V
L = 2μH
V
V
LOAD (MAX)
Modulator Gain =
where V
DROOP
DS(ON)
OUT
C2 = 33pF and use the type 2 compensation
IN
From the following formula :
scheme shown in Figure 5.
The asymptotic bode plot of EA compensation and
CORE
LC Filter Pole =
From the following formulas :
Middle Band Gain is 10 (i.e 20dB).
ESR Zero =
Select R1 = 2.4kΩ, R2 = 24kΩ, C1 = 6.6nF,
Middle Band Gain =
PWM loop gain is shown as Figure 6.
COMP
By calculation, the F
F
= 12V
Z
= 9,000μF with 2mΩ ESR.
=
= 1.5V
= 6mΩ of low side MOSFET at 27°C
= 120mV at full load
2
RAMP
π
= 60A
x
C2
: ramp amplitude of sawtooth wave
R
1
DACOUT
2π x ESR x C
-
+
2
C1
x
V
2
C
π
V
Figure 5.
RAMP
1
,
1
IN
x
R
R
Z
1
F
FB
= 1kHz, F
2
1
P
LC
=
R3,C3 are used in type
3 compensation scheme
(left NC in type 2)
OUT
=
1.9V
12V
= 1.2kHz and
2
= 8.8kHz
π
×
3
2
x
P
= 4.2 (12.46dB)
R
= 200kHz and
C3
2
x
1
⎛
⎜
⎝
C
C
1
1
×
+
C
C
VDIF
2
2
⎞
⎟
⎠
4. Soft-Start Capacitor Selection
2. Droop & DAC Offset Setting
3. Over-Current Protection Setting
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 is internally set at around 100μA of I
for each channel. As above-selected R
the OCP trip point is found using :
C
I
For each channel the load current is 60A / 3 = 20A
and the ripple current, ΔI
The load current, I
X (OCP)
Using the following formula to select the appropriate
I
100
DROOP
X (MAX)
SP
DS(ON)
ADJ
ADJ_27°C
SS
-20
-40
-60
80
60
40
20
0
Asymptotic Bode Plot of PWM Loop Gain
= R
10
= 0.1μF is the suitable value for most application.
10
at 70°C is given as :
5 s x
DS(ON)
μ
SN
at 70°C is given as :
= 120mV = 55μA × 2 × 3 (phase no.) × R
for the S/H of GM amplifier :
=
× (R
I
= 2kΩ, then I
R
100
X
100
ADJ
DS(ON)
of MOSFET varies with temperature rise.
(MAX)
1.5V
2uH
DS(ON)_27°C
will be 360Ω.
X
R
1000
=
1K
is in the order of 50 to 60μA, select
x 1
×
SP
L
R
, at S/H is
I
⎛
⎜
⎝
Figure 6.
L (TRIP)
Frequency (Hz)
DS(ON)
−
X (MAX)
10000
10K
1.5V
12V
/ R
L
, is given as :
R
Modulator Gain
DS(ON)_70°C
×
=
DS9244-06 March 2007
PWM Loop Gain
SP
will be 55μA.
Uncompensated EA Gain
⎞
⎟
⎠
18.36A
100000
20
6mΩ 33A
Compensated EA Gain
100K
=
A
2k
−
×
3.28A
Ω
1000000 10000000
Δ
) = 296Ω
1M
SP
2
I
L
= R
DS(ON)
=
18
=
SN
10M
.
100 A
36
, the
= 2kΩ,
ADJ
A
μ
.
,
X