MIC2583 Micrel Semiconductor, MIC2583 Datasheet - Page 17

• Manufacturer Part Number: MIC2583
• Description: Single Channel Hot Swap Controllers
• Manufacturer: Micrel Semiconductor

Auto-Restart - MIC2583R
The MIC2583R provides an auto-restart function. Upon an
overcurrent fault condition such as a short circuit, the
MIC2583R initially shuts off the GATE output. The MIC2583R
attempts to restart with a 12 A charge current at a preset 10%
duty cycle until the fault condition is removed. The interval
between auto-retry attempts is set by capacitor C
Sense Resistor Selection
The MIC2582 and MIC2583 use a low-value sense resistor to
measure the current flowing through the MOSFET switch
(and therefore the load). This sense resistor is nominally set
at 50mV/I
ances for both the sense resistor (allow 3% over time and
temperature for a resistor with 1% initial tolerance) and still
supply the maximum required steady-state load current, a
slightly more detailed calculation must be used.
The current limit threshold voltage (i.e., the “trip point”) for the
MIC2582/83 may be as low as 42mV, which would equate to
a sense resistor value of 42mV/I
numbers through for the case where the value of the sense
resistor is 3% high yields:
April 2003
MIC2582/MIC2583
R
SENSE(MAX)
GND
V
5V
IN
LOAD(CONT)
Backplane
Connector
1.03 I
. To accommodate worst-case toler-
PCB Edge
Connector
42mV
LOAD(CONT)
Short
(9V)
Long
Pin
D1
Pin
47k
Circuit
R1
Open
Long
LOAD(CONT)
Pin
2
3
C1
0.47 F
Figure 8. 5V Switch/3.3V LDO Application
I
LOAD(CONT)
ON
CPOR
Undervoltage (Output) = 3.3V
All resistors 5% unless specified otherwise
40.8mV
VCC
8
3
1
. Carrying the
0.010
R
SENSE
2%
MIC2582
GND
SENSE
FILTER
2
4
4
7
(11)
.
GATE
/POR
FB
17
Si4876DY
(SO-8)
6
1
5
Once the value of R
it is good practice to check the maximum I
the circuit may let through in the case of tolerance buildup in
the opposite direction. Here, the worst-case maximum cur-
rent is found using a 59mV trip voltage and a sense resistor
that is 3% low in value. The resulting equation is:
As an example, if an output must carry a continuous 2A
without nuisance trips occurring, Equation 11
yields: R
standard value is 20m . At the other set of tolerance ex-
tremes for the output in question,
Knowing this final datum, we can determine the necessary
wattage of the sense resistor using P = I
I
numbers yield the following: P
In this example, a
Q1
I
LOAD(CONT, MAX)
I
LOAD(CONT,MAX)
LOAD(CONT,MAX)
R2
10
C2
0.022 F
1.2M
V
R4
IN
Si4876DY
R8
20k
SENSE(MAX)
(SO-8)
Q2
R3
10
R9
750
C3
4700pF
, and R will be (0.97)(R
20.0m
60.8mV
0.97 R
1
/
SENSE
4
W sense resistor is sufficient.
40.8mV
59mV
2A
Q3
PN2222
SENSE(NOM)
R5
510k
has been chosen in this manner,
MAX
3
.04 , approximately 3A.
= (3A)
R6
20k
1%
R7
11.8k
1%
2
0 4 .
A
m
C6
100 F
C5
330 F
2
R
SENSE(NOM)
(19.4m ) = 0.175W.
MIC2582/MIC2583
2
SENSE(NOM)
. The next lowest
60.8mV
LOAD(CONT)
R, where I will be
C4
0.1 F
V
3.3V@0.5A
V
5V@3.5A
OUT
OUT
). These
(12)
Micrel
which