ir3084u International Rectifier Corp., ir3084u Datasheet - Page 30

• Manufacturer Part Number: ir3084u
• Description: Xphasetm Vr10, Vr11 & Opteron/athlon64 Control Ic
• Manufacturer: International Rectifier Corp.

Over Current Setting Resistor R
The inductor DC resistance is utilized to sense the inductor current. The copper wire of the inductor has a
constant temperature coefficient of 3850 PPM, and therefore the maximum inductor DCR can be calculated from
Equation (14), where R
temperature T_
The current sense amplifier gain of the IR3086A decreases with temperature at the rate of 1470 PPM, which
compensates part of the inductor DCR increase. The phase IC die temperature is only a couple of degrees
Celsius higher than the PCB temperature due to the low thermal impedance of MLPQ package. The minimum
current sense amplifier gain at the maximum phase IC temperature T
The over-current limit is set by the external resistor R
required over current limit. I
resistor R
average current in each phase and is calculated from Equation (17).
Where: V
Page 30 of 47
G
R
R
K
OSC
OCSET
L_MAX
CS_MIN
P
=
and is determined by the curve in Figure 14 on page 25. K
(V
ROOM
V
L is the value of the output inductors.
f
I
n is the number of phases.
=
=
SW
LIMIT
=
I
I
O_FL
[
R
is the input voltage to the converter (nominally 12V).
G
−
is the switching frequency.
L_ROOM
I
V
CS_ROOM
is the DC output current of the converter when the over-current fault occurs.
respectively.
LIMIT
is the output voltage of the converter with droop at the over-current threshold.
O
n
L_MAX
_
FL
∗
∗
)
OCSET,
R
∗
∗
[1
V
L_MAX
and R
[1
I
O
+
LIMIT
_
−
OCSET
3850*10
FL
1470*10
the bias current of the OCSET pin, changes with switching frequency setting
∗
/(L
L_ROOM
/n
(1
∗
+
V
K
I
−
6
P
∗
−
are the inductor DCR at maximum temperature T
6
∗
)
f
∗
+
(T
SW
(T
V
L_MAX
CS_TOFST
∗
IC_MAX
2)
−
OCSET
T
−
]
ROOM
T
∗
ROOM
G
as defined in Equation (16), where I
I
CS
)]
OCSET
_
)]
MIN
IC_MAX
P
is the ratio of inductor peak current to
is calculated from Equation (15).
IR3084U
L_MAX
(14)
(15)
(16)
(17)
9/14/2005
LIMIT
and room
is the