RT9241A RICHTEK [Richtek Technology Corporation], RT9241A Datasheet - Page 14

• Manufacturer Part Number: RT9241A
• Description: Two-Phase DC/DC Controller for CPU Core Power Supply
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9241A/B
Design Example for RT9241A
Two phase converter V
current = 40Amp, droop voltage at full load = 120mV,
OCP trip point for each power stage = 30Amp (at Sample/
Hold), low side MOSFET R
temperature, L = 2μH, C
ESR = 2mΩ.
1.Compensation setting
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14
a. Modulator Gain, Pole and Zero
b. EA compensation network
R
Fp = 200kHz, mid-band Gain = 10 = 20dB, modulator
asymptotic Bode plot of EA compensation and PWM
loop Gain Bode shown as Figure 6.
mid-band gain =
ESR zero =
Modulator Gain =
saw-tooth wave amplitude V
modulator Gain = 8.6 = 18.7dB
LC filter pole =
Use type 2 compensation scheme (see Figure5)
F =
Z
2
= 24KΩ, C
COMP
Figure 5. EA Compensation Network
2 R C
C
π
1
1
EA
2 1
C
DACOUT
2
-
+
R
1
2
2
1
π
= 6.6nF, C
CR
2
π
V
1
ESR
FP =
CORE
R
R
V
RAMP
LC
FB
2
IN
1
= 8.8kHz
= 1.2kHz
= 1.5V, V
OUT
2 R2(
R
π
2
. Choose R
R
compensation scheme
(left NC in type 2)
R
setting
DS(ON)
OL
= 33pF, get F
3
OL
C
RAMP
= 9000μF, capacitor
, C
3
for no load offset
R1
3
C1+ C2
C1 C2
1
are used in type 3
= 6mΩ at room
= 1.7V,
IN
×
R
3
= 12V, full load
)
1
= 2.4KΩ,
Z
V
= 1kHz,
CORE
2.Over Current Protection setting
3.Droop setting
4.SS capacitor
OCP trip point current = 30A (at Sample/Hold),
Take the temperature rising for consideration, if MOSFET
working temperature = 70°C and the temperature
coefficient = 5000ppm/°C, R
{R
Full load current of each power channel = 40A/2 =
20Amp, the ripple current = ΔI
, load current at S/H
required Droop = 120mV = 46μA
R
Take the temperature rising for consideration, we just
modify R
C
Figure 6. Asymptotic Bode Plot of PWM Loop Gain
I
= I
, GM Amp S/H, R
X
5 s
ADJ
SS
μ
DS(ON)
100
=
-20
-40
-60
X(MAX)
80
60
40
20
= 0.1μF is the suitable value for most application.
0
R
Asymptotic Bode Plot of PWM Loop Gain
= 1.97KΩ.
×
10
10
DS
1.5V
2 H
(70°C)/R
(
μ
ON
ISP
R
=
SP
)
R
×
100
100
×
like OCP setting.
DS(ON)
30
(1-
A
DS(ON)
1.5V
R
12V
=
1000
ISP
×
ISP
1K
75
18.36A
= R
20A -
μ
Frequency (Hz)
(27°C)} = 1.75KΩ
) = 3.28A
A
10000
ISN
10K
, R
DS9241AB-05 March 2007
Δ
Modulator Gain
ISP
= 2.4KΩ, I
2
I
PWM Loop Gain
L
L
ISP
Uncompensated EA Gain
100000
(70°C) = R
=
Compensated EA Gain
= 18.36A
100K
= 2.4KΩ
1000000 10000000
×
1M
X(MAX)
2
×
ISP
2/3
(27°C)
10M
= 46μA,
×
R
ADJ,
×