IR3081 International Rectifier Corp., IR3081 Datasheet - Page 19

• Manufacturer Part Number: IR3081
• Description: Xphasetm Vr 10 Control Ic
• Manufacturer: International Rectifier Corp.

to that of VDAC down-slope and is given by Equation (9), where I
shown in Figure15.
Over Current Setting Resistor R
The inductor DC resistance is utilized to sense the inductor current. The copper wire of inductor has a constant
temperature coefficient of 3850 ppm/°C, and therefore the maximum inductor DCR can be calculated from Equation
(10), where R
T_
The current sense amplifier gain of IR3086 decreases with temperature at the rate of 1470 ppm/°C, 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 total input offset voltage (V
(V
sense resistors R
The over current limit is set by the external resistor R
over current limit. I
and is determined by the curve in Figure 14. K
phase and is calculated from Equation (14).
No Load Output Voltage Setting Resistor R
A resistor between FB pin and the converter output is used to create output voltage offset V
difference between V
lowers the converter voltage by R
R
adaptive voltage positioning resistor R
are determined by (15) and (16) respectively.
FB
CS_OFST)
ROOM
Page 19 of 39
is not only determined by I
respectively.
of the amplifier itself and that created by the amplifier input bias currents flowing through the current
L_MAX
CS+
OCSET,
V
G
R
R
K
C
R
SR
and R
CS
OCSET
L
CS
and R
P
VDAC
VDAC
DAC
_
UP
_
=
MAX
_
TOFST
MIN
(
=
V
=
=
the bias current of OCSET pin, changes with switching frequency setting resistor R
=
voltage and output voltage at no load condition. Adaptive voltage positioning further
L_ROOM
I
CS-
I
=
0
C
=
[
−
SR
SOURCE
5 .
I
R
=
V
VDAC
I
G
LIMIT
.
SINK
L
O
DOWN
V
FB
+
n
CS
_
CS
)
O
3
ROOM
∗
, the current flowing out of FB pin as shown in Figure 14, but also affected by the
CS_TOFST
OCSET
_
2 .
*I
C
_
V
ROOM
are the inductor DCR at maximum temperature T
∗
OFST
O
VDAC
O,
∗
R
I
O
10
/(
L
DRP
where R
∗
L
_
/
−
1 [
+
2
∗
MAX
n
∗
15
1 [
I
V
+
CSIN
and total input offset voltage of current sense amplifiers. R
) of current sense amplifier in phase ICs is the sum of input offset
I
−
3850
∗
∗
1470
FB
1 (
+
f
O
SW
P
+
∗
and Adaptive Voltage Positioning Resistor R
*
is the required output impedance of the converter.
R
is the ratio of inductor peak current over average current in each
K
∗
*
10
CS
P
10
) 2
)
−
+
OCSET
6
+
−
IC_MAX
−
6
∗
V
I
∗
CS
(
CSIN
T
(
T
L
_
_
IC
TOFST
as defined in Equation (13), where I
−
MAX
_
is calculated from Equation (11).
∗
MAX
R
CS
]
−
∗
−
T
−
G
ROOM
SOURCE
T
CS
ROOM
_
MIN
)]
)]
/
I
is the source current of VDAC pin as
OCSET
L_MAX
(10)
(11)
(12)
(13)
(14)
and room temperature
(7)
(8)
(9)
O_NLOFST,
LIMIT
DRP
10/01
IR3081
is the required
FB
/04
which is the
and R
OSC
DRP