ISL6560 Intersil Corporation, ISL6560 Datasheet - Page 12

• Manufacturer Part Number: ISL6560
• Description: Microprocessor CORE Voltage Regulator Two-Phase Buck PWM Controller
• Manufacturer: Intersil Corporation

ISL6560 Supply Design Sequence
Please note several changes from the computations in the
body of the data sheet. An operating frequency of 400kHz
was chosen. A 15mV offset voltage was added to the no-
load output voltage to show the design procedure.
ISL6560 Supply Design Sequence
A. Specifications:
B. Calculate R
C. Determine Frequency Setting Capacitor CT:
D. Select Inductor Ripple Current (∆I
E. Determine the Inductors:
FIGURE A. OSCILLATOR FREQUENCY vs. TIMING
From curve of Figure A, for 400kHz use 120pF.
Choose 40% of IOUT:
L
R
∆I
=
Or 8A / Channel
=
Output Current:
OUT
Input Voltage:
Output Voltage: VDAC + 15mV
Output Voltage for Calculations:
V
Droop Voltage: 65mV
Oscillator Frequency: 400kHz (f
3000
1000
L
V
--------------------------------- -
DAC
100
956nH
f SW
----------- -
IN
=
2
40A
=
0
–
= 1.8V + 15mV
V
×
V
----------------------- -
CAPACITOR
OUT
∆I
DROOP
I
×
50
OUT
OUT
L
0.4
×
100 150 200 250 300
:
=
V
-----------------
V IN
OUT
12V
=
40A
16A
65mV
--------------- -
40A
CAPACITOR CT (pF)
=
-----------------------------------
200kHz
12V 1.8V
12
=
1.63mΩ
SW
–
)
×
8A
×
L
350 400
):
1.8V
------------
12V
450 500
ISL6560
F. Output Capacitors:
G. Input Capacitor’s RMS Current:
For 40A with a duty cycle (D) of:
H. Current Sense Resistor (R
I. R
J. R
G. Input Capacitor’s RMS Current:
Use the curve of Figure B.
SENSE
L
Six capacitors < 1.66mΩ
Total Capacitance = 9mF
R
Capacitor
Panasonic 470µF, 16V Rubycon ZA series capacitors
have a RMS current rating of 1.6A.
Six capacitors were selected.
Sanyo 1500µF, 4V OS-CON Capacitors
∴
SENSE
Selection:
Where: I
FIGURE B.
Used two 10mΩ, 1W resistors in parallel.
Power
Power
Power
gm Amplifier Gain
have an ESR < 10mΩ
I
I
RMS
RMS
0.3
0.2
0.1
R L
0
The multiplier from Figure B is 0.24.
D
Dissipation:
0
=
=
=
P
ESR
=
=
=
=
=
----------------------------------------
gm
0.24
= 34.4A -4A = 30.4A
V
---------------
ni
30.4
------------------------------------------
I
------------ -
I
V
I P
0.69W per channel or 1.38W for both channels
OUT
Use a 5mΩ resistor
OUT
PEAK
V
2
×
IN
×
2
≅
CS TH
CURRENT MULTIPLIER vs. DUTY CYCL
×
R
R
0.1
×
R
A
40A
SENSE
+
OUT
(
D
=
2
OUT
I
--------------------- -
D
RIPPLE
×
×
1.8V
------------
12V
)MIN
=
0.15
R
=
×
2
DUTY CYCLE (V
SENSE
gm
2
=
9.6A
0.2
=
=
×
1.63mΩ
×
5mΩ
=
0.15
------------------------------------------------------- -
2.2mS
RL
------------------------ -
20A
SENSE
142mV
=
12.5 5mΩ
(Using half the ripple current)
2.2mS
+
×
O
0.3
8A
1.63mΩ
/ V
×
):
(continued)
IN
=
)
×
5.07mΩ
8.7k
×
0.4
2
=
=
19.1
8.7kΩ
E
0.5