MIC2582 MICREL [Micrel Semiconductor], MIC2582 Datasheet - Page 20

• Manufacturer Part Number: MIC2582
• Description: Single Channel Hot Swap Controllers
• Manufacturer: MICREL [Micrel Semiconductor]

MIC2582/MIC2583
two iterations, But it’s not a hard calculation to perform, and
tends to converge quickly.
Then the starting (steady-state)T
Iterate the calculation once to see if this value is within a few
percent of the expected final value. For this iteration we will
start with T
MIC2582/MIC2583
T
T
T
T
T
J
J
J
J
J
Figure 11. Recommended PCB Layout for Sense Resistor, Power MOSFET, and Feedback Network
( 55 C + (0.125W)(50 C/W)
T
T
55 C + [17m + (55 C-25 C)(0.005)(17m )]
(55 C + (0.122W)(50 C/W)
61.1 C
T
J
A(MAX)
A(MAX)
A
equal to the already calculated value of 61.1 C:
+ [17m + (61.1 C-25 C)(0.005)(17m )]
x (2.5A)
x (2.5A)
+ T
+ [R
x I
0.01
0.1
2
2
2
1
x R
ON
J
10
x (50 C/W)
2
–4
Duty Cycle = 0.5
0.2
0.1
0.05
0.02
x (50 C/W)
+ (T
(J-A)
A(MAX)
Current Flow
to the Load
J
W
is:
W
Single Pulse
10
– T
–3
Figure 10. Transient Thermal Impedance
DRAWING IS NOT TO SCALE
*See Table 4 for part numbers and vendors.
**Optional components.
Trace width (W) guidelines given in "PCB Layout Recommendations" section of the datasheet.
Normalized Thermal Transient Impedance, Junction-to-Ambient
A
61.27 C
)(0.005/ C)(R
Current Flow
to the Load
*SENSE RESISTOR
10
8
1
–2
(2512)
Square Wave Pulse Duration (sec)
ON
7
2
**C
POR
)]
6
3
20
So our original approximation of 61.1 C was very close to the
correct value. We will use T
Finally, add (11.25W)(50 C/W)(0.08) = 45 C to the steady-
state T
able maximum junction temperature for this part.
PCB Layout Considerations
Because of the low values of the sense resistors used with the
MIC2582/83 controllers, special attention to the layout must
be used in order for the device’s circuit breaker function to
operate properly. Specifically, the use of a 4-wire Kelvin
connection to accurately measure the voltage across R
is highly recommended. Kelvin sensing is simply a means of
making sure that any voltage drops in the power traces
connecting to the resistors does not get picked up by the
traces themselves. Additionally, these Kelvin connections
should be isolated from all other signal traces to avoid
introducing noise onto these sensitive nodes. Figure 11
illustrates a recommended, single layer layout for the R
10
5
4
–1
D
D
D
D
*POWER MOSFET
J
**C
12.4k
to get T
(SO-8)
1%
GATE
**R
GATE
G
S
S
S
93.1k
1%
1
J(TRANSIENT MAX.)
Notes:
1. Duty Cycle, D =
2. Per Unit Base = R
3. T
4. Surface Mounted
Current Flow
to the Load
P
DM
JM
– T
t
1
A
= P
t
2
DM
W
Z
J
thJA
t
t
thJA
1
2
10
= 61 C.
(t)
= 50 C/W
= 106 C. This is an accept-
30
April 2003
SENSE
Micrel
SENSE
,