MIC2587 Evaluation Board
Single Channel, Positive-Voltage
Hot Swap Controller
General Description
MIC2587/MIC2587R Hot Swap Controller
The MIC2587 is a single-channel, positive-voltage hot-
swap controller designed to address the need for safe
insertion and removal of circuit boards into electrically
live system backplanes. With few external components,
the controller works in conjunction with an external N-
Channel MOSFET to provide inrush current limiting and
gate slew-rate control. Additionally, the current limit is
user-programmable and works in conjunction with a
user-programmable overcurrent timer to provide reliable
overcurrent fault protection to the system’s circuit
components. During an output overload condition, a
constant-current regulation loop is engaged to ensure
that the system power supply maintains regulation. As a
means to reduce the power consumption in the presence
of a severe overcurrent load, the MIC2587 is equipped
with a circuit that monitors the voltage level at the FB
pin, and once engaged, allows for the current limit to
“foldback” to a lower threshold to effectively reduce the
regulated current limit. Once the overcurrent timer
expires, the output of the MIC2587 is latched off and can
be reset by toggling the ON pin from high-to-low-to-high.
The MIC2587R will automatically restart the turn-on
cycle with a fixed duty cycle (≈ 5%) after the overcurrent
timer has expired. A master Power-Good signal is
provided to indicate that the output voltage of the soft-
start circuit is within its valid output range. The Power-
Good signal can be used to enable one or more
downstream DC-DC converter modules.
MIC2587 Evaluation Board
The MIC2587 evaluation board is designed to showcase
the power switching capability of the MIC2587 controller.
The board is configured for switching 24V or 48V with a
nominal current limit of 4.7A. Several test points are
included for the user to monitor the response of a
number of pins (e.g. VIN, GATE, TIMER, and /PWRGD).
The Power-Good signal is an open-drain output, with
asserted status as either high impedance (-1) or active-
Low (-2). Additionally, banana plugs are provided to
allow for the use of high-current electrical cables to
transfer the necessary current through the power
MOSFET and to the load. See the
Operation
section for
details on how to select the values for these components
for desired system requirements. (Please refer to the
MIC2587 datasheet for detailed pin descriptions and
additional support information.)
Basic Requirements
The MIC2587 controller requires a minimum of 10V for
operation, and the evaluation board is configured to
operate with 24V or 48V, depending upon the resistor
divider networks that are shown in a table inserted in the
circuit schematic.
Precautions
Unless the range of voltages over which the intended
application for the MIC2587/MIC2587R controller is well
controlled and carefully observed, the input and output
capacitors should have a maximum voltage rating of at
least 100V. Thus, the rating of these capacitors is at
minimum equivalent to the 100V transient maximum
voltage rating of the MIC2587 integrated circuits.
Note:
The input capacitor should be an aluminum
electrolytic device, as most tantalum capacitors in this
voltage range are not capable of safely handling the
surge currents that will flow through C
IN
during a hot-plug
event. C
OUT
, however, may be a tantalum capacitor as
the MIC2587 controls the di/dt and dv/dt seen by C
OUT
.
Ordering Information
Part Number
MIC2587-1BM EV
MIC2587R-1BM EV
Description
Evaluation board with the
MIC2587-1BM device
Evaluation board with the
MIC2587R-1BM device
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
October 2008
M9999-102108-A
Micrel, Inc.
MIC2587/MIC2587R Evaluation Board
Current Limit
The current-limit is determined using the following
formula:
I
LIM
= V
TRIP
/ R
SENSE
(1)
where V
TRIP
is the circuit breaker threshold obtained from
the Electrical Characteristics Table in the MIC2587
datasheet. For the MIC2587 evaluation board, the
nominal current limit I
LIM
= 47mV/10mΩ = 4.7A. Using
Equation 1 and some basic algebra, the value for R
SENSE
can be determined given a desired current-limit by:
R
SENSE
= V
TRIP
/ I
LIM
The circuit breaker is ‘tripped’ upon an overcurrent
condition that lasts longer than the time period t
FLT
,
which is set by capacitor C
TIMER
(C7). If C
TIMER
= 0, t
FLT
=
t
OCSENSE
, the default value of 2µs. C
TIMER
may be
determined for a desired t
FLT
using the following
formula
1
.
C
TIMER
= (I
TIMERUP
∗
t
FLT
) / V
TIMERH
(2)
where I
TIMER
, the typical current-limit timer current, is
65μA, and V
TH
, the typical timer threshold, is 1.313V.
Both values are found in the Electrical Characteristics
Table of the datasheet. Substituting these values into
Equation 2, the result is now approximated by:
C
TIMER
≅
50x10
-6
(A/V)
∗
t
FLT
For a 6ms overcurrent delay, the calculated value for
C
TIMER
is 0.3µF. The closest standard value is 0.33µF.
Programmable Output Slew Rate (C
GATE
)
Capacitor C
GATE
is used to set the output slew rate and
limit the inrush current. An external GATE capacitor,
C
GATE
, sets the GATE output rise-time (or slew rate) to
turn on the external Power MOSFET. The source
(output) of the MOSFET then follows the GATE once the
GATE voltage exceeds the V
G-S
threshold. The rise time
is determined by the following equation:
t
RISE
≅
(ΔV
∗
C
TOTAL
) / I
GATE
(3)
where
ΔV
= V
IN
+ 13V (13V typical enhancement for
MIC2587 GATE output for 10V
≤
V
CC
≤
80V) and I
GATEON
is the nominal GATE pin pull-up current. The total
capacitance that the GATE must drive is the external
C
GATE
plus the parasitic capacitance, C
G-S
, of the
external MOSFET. For the SUM110N10-09, C
G-S
is
approximately 6.5nF. Given the following conditions:
V
IN
= V
OUT
= 24V and C
GATE
= 47nF
t
RISE
≅
(13V
∗
53.5nF)/16µA
≅
15ms.
R7 is used for stabilization of the current limit control
loop.
Operation
External Switch
The MIC2587 requires an external N-Channel MOSFET
to serve as the power switch device. The MIC2587 pin
connections for the MOSFET terminals and sense
resistor are shown in the attached circuit schematic. The
SUM110N10-09, a power MOSFET in a TO-263
package from Vishay, is used as the pass device on the
evaluation boards. Several MOSFET devices suited for
use with the MIC2587 are listed in Table 3 at the end of
the datasheet.
The ON control pin will switch the external MOSFET on
when the voltage at ON is greater than the specified
threshold voltage of 1.24V (typical). This pin exhibits
50mV of hysteresis. A three terminal jumper (J1) is used
to either pull-up the ON pin to VCC (through an external
resistive divider) or tie the pin-to-ground to disable the
controller.
Component Selection for Various V
IN
Table 1 below displays the resistor values selected to
configure the MIC2587 controller with various input
voltages. The two resistor combinations are
implemented as resistive divider networks to attain
specific turn-on/turn-off and “Power-is-Good” thresholds.
These values are used for reference, but for different
threshold requirements, alternative resistor combinations
may be chosen that satisfy Equations 8 and 9 from the
MIC2587 datasheet.
+16V
R1
R2
R5
R8
V
IN(ON)
V
IN(OFF)
V
OUT(GOOD)
V
OUT(NOT_GOOD)
95.3kΩ
10.0kΩ
35.7kΩ
3.57kΩ
13.8V
13.0V
14.4V
13.5V
+24V
49.9kΩ
3.40kΩ
59.0kΩ
3.57kΩ
20.6V
19.3V
23.0V
21.6V
+32V
261kΩ
12.4kΩ
93.1kΩ
4.22kΩ
29.0V
27.0V
30.3V
28.4V
+48V
287kΩ
10.0kΩ
143kΩ
4.22kΩ
39.0V
36.6V
45.8V
43.0V
Table1. Resistor Combinations for
Various System Voltage Levels
October 2008
2
M9999-102108-A
Micrel, Inc.
MIC2587/MIC2587R Evaluation Board
Circuit Schematic
TP1
VCC
BJ1
VCC
C1
47µF
R1
287k
R2
10k
C2
0.1µF
JP1
ON
C3
0.1µF
C5
0.1µF
D1
SMBG100A
U1
MIC2587/87R
ON
FB
PWRD
GND
VCC
SENSE
GATE
CTIMER
R4
D2
MMBZ5248
R5
143k
TP10
FO
TP8
SENSE
TP7
CTIMER
R7
1k
TP9
GATE
C8
0.01µF
R8
4.22k
+VCC
R3
Q1
SUB85N10-10
C4
0.1µF
VOUT
C6
100µF
BJ2
+VOUT
TP3
OUT
R6
47.5k
TP4
PWRGD
BJ3
GND
TP5
GND
TP6
GND
TP2
ON
1
2
3
4
8
7
6
5
C7
1µF
R1
R2
R5
R8
+48V
287k
10k
143k
4.22k
+24V
49.9k
3.4k
59k
3.57k
Figure 1. MIC2587 EVB Circuit Schematic
October 2008
3
M9999-102108-A
Micrel, Inc.
MIC2587/MIC2587R Evaluation Board
Bill of Materials
Item
BJ1-BJ3
C1
C2-C4
C5
C6
C7
C8
D1
D2
J1
MH1-MH4
MH1-MH4
R1
R2
R3
R4
R5
R6
R7
R8
Q1
TP1-TP10
U1
Notes:
1.
2.
3.
4.
5.
6.
7.
Johnson: www.tdk.com
Vishay: www.vishay.com
AVX: www.avx.com
Molex: www.molex.com
Tyco: www. tycoelectronics.com
Keystone: www.keyeleco.com
Micrel, Inc.: www.micrel.com
Part Number
108-0740-001
2222 038 59479
VJ0805V104MXBCW1BC
VJ0805A331FXBAB
2222 0385 9101
CF162E0105J
VJ0805V103MXBCW1BC
SMBG100A/2
MMBZ5248B-GS08
22-03-2021
881545-2
534-2211
5721-632-3/8
CRCW080549K9FKTA
CRCW08053K40FKTA
WSR2R0100FTA
CRCW080510R0FKTA
CRCW080559K0FKTA
CRCW080547K5FKTA
CRCW08051K002FKTA
CRCW08053K57FKTA
SUM110N10-09
1593-2
MIC2587-1BM or
MIC2587R-1BM
Manufacturer
Johnson
(1)
Vishay
(2)
Vishay
(2)
Vishay
Vishay
AVX
(2)
(2)
Description
Banana Jack, 0.256" H/S
Electrolytic Capacitor, 47µF, 100V, 20%, Size 10x12
Ceramic Capacitor, 0.1µF, 100V, 20%, Y5V, Size 0805
Ceramic Capacitor, 330pF, 100V, 1%, COG, Size 0805
Electrolytic Capacitor, 100µF, 100V, 20%, Size 10X12
Ceramic Capacitor, 1µF, 100V, 20%, PET-HT, Size 4030
Ceramic Capacitor, 0.01µF, 100v, 20%, Y5V, Size 0805
Transzorb Diode, 100V
Zener Diode, 18V,5%
Jumper, 2-pin, 0.1” Center, 0.35” Hole
Jumper Shunt
Stand-off - 5/8", 6-32,Hex
Machine Screws, 6-32 x 3/8
Resistor, 49.9K, 1%, Size 0805
Resistor, 3.4K, 1%, Size 0805
Resistor, 0.01Ω, 1%, 2w, Size 4527
Resistor, 10Ω, 1%, Size 0805
Resistor, 59k, 1%, Size 0805
Resistor, 47.5k, 1%, Size 0805
Resistor, 1k, 1%, Size 0805
Resistor, 3.57k, 1%, Size 0805
N-Channel, 100V, MOSFET
Turret Terminal, 0.065" H/S
Single Channel, Positive-Voltage
Hot Swap Controller
Qty.
3
1
3
1
1
1
1
1
1
1
1
4
4
1
1
1
1
1
1
1
1
1
10
1
(3)
Vishay
(2)
Vishay
(2)
Vishay
(2)
Molex
(4)
Tyco
(5)
(6)
Keystone
Keystone
(6)
Vishay
(2)
Vishay
(2)
Vishay
(2)
Vishay
(2)
(2)
(2)
Vishay
Vishay
Vishay
(2)
Vishay
(2)
Vishay
(2)
Keystone
(6)
Micrel
(7)
October 2008
4
M9999-102108-A
Micrel, Inc.
MIC2587/MIC2587R Evaluation Board
PCB Layout Recommendation
Top Assembly
Top Layer
October 2008
5
M9999-102108-A
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