MIC2587/MIC2587R
Single-Channel, Positive High-Voltage
Hot Swap Controller
Revision 2.0
General Description
The MIC2587 and MIC2587R are single-channel positive
voltage hot swap controllers designed to provide safe
insertion and removal of boards for systems that require
live (always-powered) backplanes. These devices use few
external components and act as controllers for external N-
channel power MOSFET devices to provide inrush current
control and output voltage slew rate control. Overcurrent
fault protection is provided via programmable analog fold-
back current-limit circuitry equipped with a programmable
overcurrent filter. These protection circuits combine to limit
the power dissipation of the external MOSFET to ensure
that the MOSFET is in its SOA during fault conditions. The
MIC2587 provides a circuit breaker function that latches
the output MOSFET off if the load current exceeds the
current limit threshold for the duration of the programmable
timer. The MIC2587R provides a circuit breaker function
that automatically attempts to restart power after a load
current fault at a low duty cycle to prevent the MOSFET
from overheating. Each device provides either an active-
HIGH (−1YM) or an active-LOW (−2YM) “Power-is-Good”
signal to indicate that the output load voltage is within
tolerance of the application circuit’s design objective.
Datasheets and support documentation are available on
Micrel’s web site at:
www.micrel.com.
Features
•
MIC2587: Pin-for-pin functional equivalent to the
LT1641
•
Operates from +10V to +80V with 100V ABS MAX
operation
•
Programmable current limit with analog foldback
•
Active current regulation minimizes inrush current
•
Electronic circuit breaker for overcurrent fault protection:
−
Output latch off (MIC2587)
−
Output auto-retry (MIC2587R)
•
Fast responding circuit breaker (< 1
o short
s
) t
circuit
loads
•
Programmable input undervoltage lockout
•
Open-drain “Power-is-Good” output for enabling DC/DC
converter(s):
−
Active-HIGH: MIC2587-1/MIC2587R-1
−
Active-LOW: MIC2587-2/MIC2587R-2
•
Fault Reporting
Applications
•
•
•
•
•
•
General-purpose hot board insertion
High-voltage, high-side electronic circuit breaker
+12V/+24V/+48V distributed power systems
+24V/+48V industrial/alarm systems
Telecom systems
Medical systems
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 •
http://www.micrel.com
January 24, 2013
Revision 2.0
Micrel, Inc.
MIC2587/MIC2587R
Typical Application
January 24, 2013
2
Revision 2.0
Micrel, Inc.
MIC2587/MIC2587R
Ordering Information
Part Number
MIC2587-1YM
MIC2587-2YM
MIC2587R-1YM
MIC2587R-2YM
PWRGD Polarity
Active-HIGH
Active-LOW
Active- HIGH
Active-LOW
Circuit Breaker Function
Latched
Latched
Auto-retry
Auto-retry
Package
8-Pin SOIC
8-Pin SOIC
8-Pin SOIC
8-Pin SOIC
Finish
Pb-Free
Pb-Free
Pb-Free
Pb-Free
Pin Configuration
8-pin SOIC (M)
MIC2587-1YM
MIC2587R-1YM
(Top View)
8-pin SOIC (M)
MIC2587-2YM
MIC2587R-2YM
(Top View)
Pin Description
Pin Number
Pin Name
Pin Function
Enable Input: When the voltage at the ON pin is higher than the V
ONH
threshold, a start cycle is
initiated. An internal current source (I
GATEON
) is activated which charges the GATE pin, ramping
up the voltage at this pin to turn on an external MOSFET. Whenever the voltage at the ON pin is
lower than the V
ONL
threshold, an undervoltage lockout condition is detected and the I
GATEON
current source is disabled while the GATE pin is pulled low by I
GATEOFF
. After a load current fault,
toggling the ON pin LOW then back HIGH will reset the circuit breaker and initiate another start
cycle.
Output Voltage Feedback Input: This pin is connected to an external resistor divider that is used
to sample the output load voltage. The voltage at this pin is measured against an internal
comparator whose output controls the PWRGD (or /PWRGD) signal. PWRGD (or /PWRGD)
asserts when the FB pin voltage crosses the V
FBH
threshold. When the FB pin voltage is lower
than its V
FBL
threshold, PWRGD (or /PWRGD) is de-asserted. The FB comparator exhibits a
typical hysteresis of 80mV.
The FB pin voltage also affects the MIC2587/MIC2587R’s foldback current limit operation (see
the “Functional Description” section for further information).
1
ON
2
FB
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Micrel, Inc.
MIC2587/MIC2587R
Pin Description (Continued)
Pin Number
Pin Name
Pin Function
Power-is-Good (PWRGD or /PWRGD), Open-Drain Output: This pin remains de-asserted during
start up while the FB pin voltage is below the V
FBH
threshold. Once the voltage at the FB pin
rises above the V
FBH
threshold, the Power-is-Good output asserts with minimal delay
(typically
≤
5µs).
For the (−1) options, the PWRGD output pin will be high-impedance when the FB pin voltage is
higher than V
FBH
and will pull down to GND when the FB pin voltage is less than V
FBL
.
For the (−2) options, the /PWRGD output pin will be high-impedance when the FB pin voltage is
lower than V
FBL
and will pull down to GND when the FB pin voltage is higher than V
FBH
.
The Power-is-Good output pin is connected to an open-drain, N-channel transistor implemented
with high-voltage structures. These transistors are capable of operating with pull-up resistors to
supply voltages as high as 100V.
To use this signal as a logic control in low-voltage DC/DC conversion applications, an external
pull-up resistor between this pin and the logic supply voltage is recommended unless the DC/DC
module or other load is equipped with a internal pull-up impedance.
4
GND
Tie this pin directly to the system’s analog GND plane.
Current-Limit Response Timer: A capacitor connected from this pin to GND sets the time (t
FLT
)
for which the controller is allowed to remain in current limit before “tripping” the circuit breaker.
The overcurrent filter is designed to prevent nuisance “tripping” of the circuit breaker that can be
caused by transient current spikes or other undesired “noise”. Once the MIC2587 circuit breaker
trips, the output latches off. Under normal (steady-state) operation, the TIMER pin is held to
GND by an internal 3.5µA current source (I
TIMERDN
). When the voltage across the external sense
resistor exceeds the V
TRIP
threshold, an internal 65µA current source (I
TIMERUP
) is activated to
charge the capacitor connected to the TIMER pin. When the TIMER pin voltage reaches the
V
TIMERH
threshold, the circuit breaker is tripped pulling the GATE pin low, the I
TIMERUP
current
source is disabled, and the TIMER pin capacitor is discharged by the I
TIMERDN
current source.
When the voltage at the TIMER pin is less than 0.5V, the MIC2587 can be restarted by toggling
the ON pin LOW then HIGH.
For the MIC2587R, the GATE output attempts another start cycle to re-establish the output
voltage when the circuit breaker is tripped upon an overcurrent fault. The capacitor connected to
the TIMER pin sets the period of auto-retry with a fixed, nominal duty cycle of 5%.
Gate Drive Output: This pin is the output of an internal charge pump connected to the gate of an
external, N-channel power MOSFET. The charge pump has been designed to provide a
minimum gate drive (∆V
GATE
= V
GATE
−
V
CC
) of +7.5V over the input supply’s full operating range.
When the ON pin voltage is higher than the V
ONH
threshold, a 16µA current source (I
GATEON
)
charges the GATE pin.
When in current limit, the output voltage at the GATE pin is adjusted so that the voltage across
the external sense resistor is held equal to V
TRIP
while the capacitor connected to the TIMER pin
charges. If the current limit condition goes away before the TIMER pin voltage rises above the
V
TIMERH
threshold, then steady-state operation resumes.
The GATE output pin is shut down whenever: (1) the input supply voltage is lower than the V
UVL
threshold, (2) the ON pin voltage is lower than the V
ONL
threshold, (3) the TIMER pin voltage is
higher than the V
TIMERH
threshold, or (4) the difference between the VCC and SENSE pins is
greater than V
TRIP
while the TIMER pin is grounded. For cases (3) and (4) – overcurrent fault
conditions – the GATE is immediately pulled to ground by I
GATEFLT
, an 80mA pull-down current
source.
3
PWRGD
(MIC2587-1)
(MIC2587R-1)
Active-HIGH
/PWRGD
(MIC2587-2)
(MIC2587R-2)
Active-LOW
5
TIMER
6
GATE
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Micrel, Inc.
MIC2587/MIC2587R
Pin Description (Continued)
Pin Number
Pin Name
Pin Function
Circuit Breaker Sense Input: This pin is the (−) Kelvin sense connection for the output supply rail.
A low-valued resistor (R
SENSE
) between this pin and the VCC pin sets the circuit breaker’s
current-limit trip point. When the current-limit detector circuit is enabled (as well as the current
limit0020timer), while the FB pin voltage remains higher than 1V, the voltage across the sense
resistor (V
CC
−
V
SENSE
) will be regulated to V
TRIP
(47mV, typically) to maintain a constant current
into the load. When the FB pin voltage is less than
≅
0.5V, the circuit breaker trip voltage
decreases linearly to 12mV (typical) when the FB pin voltage is at 0V.
To disable the circuit breaker (and defeat all current-limit protections), the SENSE pin and the
VCC pin can be tied together.
Positive Supply Voltage Input: This pin is the positive supply input to the controller and the (+)
Kelvin sense connection for the output supply rail. The nominal operating voltage range for the
MIC2587 and the MIC2587R is +10V to +80V, and VCC can withstand input transients up to
+100V. An undervoltage lockout circuit holds the GATE pin low whenever the supply voltage to
the MIC2587 and the MIC2587R is less than the V
UVH
threshold.
7
SENSE
8
VCC
January 24, 2013
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Revision 2.0
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