rt9237 ETC-unknow, rt9237 Datasheet - Page 11

• Manufacturer Part Number: rt9237
• Description: Multi-phase Dc/dc Controller Core Power Supply
• Manufacturer: ETC-unknow

Design Example
Three phase converter V
load current = 60Amp, droop voltage at full load =
120mV, OCP trip point for each power stage =
30Amp (at Sample/Hold), low side MOSFET R
= 6mΩ at room temperature, L = 2µH, C
9000µF, capacitor ESR = 2m Ω.
1. Compensation setting
DS9237-00 January 2002
b. EA compensation network
a. Modulator Gain, Pole and Zero
ESR zero =
Use type 2 compensation scheme (see Fig. 5),
,
mid-band gain =
24KΩ, C
Fp = 200KHz, mid-band Gain=10=20dB,
modulator asymptotic Bode plot of EA
compensation and PWM loop Gain Bode
shown as Fig. 6.
Modulator Gain =
amplitude
= 39K, V
18.7dB, LC filter pole =
F
Z
=
COMP
2
π
C
Fig. 5 EA Compensation Network
R
1
1
1
RAMP
2
C
EA
= 6.6nF, C
C
1
V
2
_
2
1
RAMP
DACOUT
R
,
π
= 1.4V, modulator Gain = 8.6 =
2
CR
F
P
R
R
=
ESR
=
2
1
V
CORE
1
V
. Choose R
2
RAMP
V
2
FB
=
π
= 33pF, get F
IN
×
R
8
56
R
2
2
8 .
π
= 1.5V, V
(
IMP
k
kHz
C
C
R
1
1
, saw-tooth wave
Ω
LC
1
1
OL
C
R
compensation scheme (left
NC in type 2)
×
+
R
setting
3
3
C
OL
C
, choose R
, C
R
=
2
1
2
1
1
for no load offset
)
3
= 2.4KΩ, R
2 .
are used in type 3
IN
R
Z
kHz
3
= 1KHz,
= 12V, full
,
OUT
DS(ON)
IRMP
V
2
Preliminary
CORE
=
=
4. SS capacitor
2. Droop setting
3. Over Current Protection setting
Full load current of each power channel = 60A/3 =
, load current at S/H =
Take the temperature rising for consideration, if
Take the temperature rising for consideration,
20Amp, the ripple current = ∆I
Amp S/H
at full = 40µA〜50µA, choose R
I
40.8µA×3×2/3×R
MOSFET working temperature=70°C and the
temperature coefficient =5000ppm/°C, the
R
5000ppm/°C} = 7.3 mΩ, R
× {R
OCP trip point current = 30A (at Sample/Hold)，
R
{R
C
application.
X(MAX)
100
-20
-40
-60
DS(ON)
IMAX
SS
I
80
60
40
20
DS(ON)
X
Fig. 6 Asymptotic Bode Plot of PWM Loop Gain
0
Asymptotic Bode Plot of PWM Loop Gain
5
10
DS(ON)
=
10
= 0.1µF is the suitable value for most
µ
S
R
(70°C) = R
= 40.8µA, required Droop = 120mV =
DS
×
(70°C) = 6mΩ × {1+(70°C-27°C) ×
(27°C)/R
1
2
(
100
ON
5 .
I
R
(27°C)/R
100
µ
( X
H
SP
V
)
MAX
×
×
30



)
1
IMAX
1000
ADJ
1K
=
A
DS(ON)
−
R
DS(ON)
1
=
12
5 .
DS
Frequency (Hz)
，R
(27°C) ×
3
2
V
V
(
20
×
10000
ON
10K
(70°C)} = 11.2KΩ



ADJ
R
R
A
0
=
)
(70°C)} = 1.21KΩ
ADJ
IMAX
6 .
SP
×
Modulator Gain
−
. 3
18
PWM Loop Gain
V
= 1.47KΩ.
Uncompensated EA Gain
28
∆
100000
(70°C) = R
2
L
Compensated EA Gain
.
100K
I
www.richtek-ic.com.tw
36
L
，R
=
A
SP
=
A
18
RT9237
= R
, suggested I
IMAX
1000000 10000000
.
36
1M
SN
A
=13.6KΩ
ADJ
= 2.7KΩ,
, GM
10M
(27°C)
11
X