ir3084a International Rectifier Corp., ir3084a Datasheet - Page 37

• Manufacturer Part Number: ir3084a
• Description: Xphase Tm Vr 10/11 Control Ic
• Manufacturer: International Rectifier Corp.

Over Current Setting Resistor R
Assume that room temperature is 25ºC and the target PCB temperature is 100 ºC. The phase IC die temperature
is usually about 1 ºC higher than that of phase IC and the inductor temperature is close to PCB temperature.
Calculate the Inductor’s DC resistance at 100 ºC using Equation (14);
The current sense amplifier gain is 34 at 25ºC, and its gain at 101ºC is calculated using Equation (15),
Here we will set the over current shutdown threshold to 155A at maximum operating temperature. From Figure
14 on page 23, the bias current of the OCSET pin (I
amplifier input offset voltage calculated previously is 0.574mV, which includes the offset created by the current
sense amplifier input resistor mismatch.
Calculate the constant K
(17);
Finally, calculate the over-current setting resistor using Equation (16);
G
=
R
K
R
L_MAX
OCSET
CS_MIN
P
(
155
Page 37 of 45
=
7
(
=
V
=
∗
=
R
I
. 0
[
L_ROOM
G
−
77
R
V
CS_ROOM
LIMIT
O
n
*
)
10
∗
∗
V
[1
∗
−
I
3
O
P,
LIMIT
∗
R
+
∗
/(
[1
the ratio of inductor peak current over average current in each phase using Equation
L_MAX
3850*10
(
L
1
−
+
∗
/
n
1470*10
V
. 0
∗
I
OCSET
273
(1
∗
−
6
+
f
∗
SW
)
K
+
(T
−
∗
P
. 0
L_MAX
6
)
) 2
574
∗
+
(T
V
=
−
CS_TOFST
IC_MAX
*
(
T
12
10
ROOM
OCSET
−
−
3
. 1
)
−
)]
]
∗
18
T
∗
=
42
ROOM
) is 42.5 A with R
)
0.
G
∗
I
5 .
60
CS
30
OCSET
. 1
*10
*
_
)]
18
2 .
MIN
10
=
/(
−
−
3
34
3
220
∗
=
[1
155
∗
15.8K
*
+
[1
10
3850*10
7 /
OSC
−
−
1470*10
9
Ω
∗
=30.1k
12
−
∗
6
∗
400
(100
−
6
∗
*
(101
10
−
IR3084A
25)]
3
10/30/2006
∗
−
) 2
=
25)]
. 0
=
77
. 0
=
273
m
30.
Ω
2