MIC2586-1YM Micrel Inc, MIC2586-1YM Datasheet - Page 11

• Manufacturer Part Number: MIC2586-1YM
• Description: IC CTRLR/SEQ HOT SWAP 14-SOIC
• Manufacturer: Micrel Inc
• Type: Hot-Swap Controllerr

Specifications of MIC2586-1YM

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 10 V ~ 80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 14-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-2197; MIC2586-1YM

the control element in a circuit that lowers the current limit as
a function of the output voltage. When the load current
increases to the point where the output voltage at the load
approaches 0V (likewise, the MIC2586/MIC2586R’s FB pin
voltage also approaches 0V), the result is a proportionate
decrease in the maximum current allowed into the load. This
foldback current limit subcircuit’s transfer characteristic is
shown in Figure 1. Under excessive load conditions (output
and FB voltage equals 0V), the foldback current limiting
circuit controls the MIC2586/MIC2586R’s GATE drive to
force a constant 12mV (typical) voltage drop across the
external sense resistor.
Circuit Breaker Operation
The MIC2586/MIC2586R employ an electronic circuit breaker
that protects the external N-channel power MOSFET and
other system components against large-scale output current
faults, both during initial card insertion or during steady-state
operation. The current-limit threshold is set via an external
resistor, R
SENSE pin. For the MIC2586/MIC2586R, a fault current
timing circuit is set via an external capacitor (C
determines the length of the time delay (t
controller remains in current limit before the circuit breaker is
tripped. Programming the response time of the overcurrent
detector helps to prevent nuisance tripping of the circuit
breaker because of high inrush currents charging bulk and
distributed capacitive loads.
response time is calculated using the following equation:
Whenever
MIC2586/MIC2586R’s nominal circuit breaker threshold
voltage of 47mV during steady-state operation, two things
occur:
Micrel
October 2004
1. A constant-current regulation loop will engage within
2. Capacitor C
t
t
FLT
FLT
(ms)
(ms)
1µs after an overcurrent condition is detected by
R
voltage across R
protects both the load and the MIC2586/MIC2586R
circuits from excessively high currents.
threshold (1.313V) by an internal 65µA current
source (I
such that the voltage across C
V
GATE pin is immediately pulled low by a 30mA
(minimum) internal current sink. This operation turns
off the MOSFET quickly and disconnects the input
from the load. The value of C
to allow the circuit's minimum regulated output
current (I
TIMERH
SENSE
SENSE
=
=
the
20
C
, and the control loop is designed to hold the
, connected between the circuit’s V
FILTER
×
threshold, the circuit breaker trips and the
OUT
TIMERUP
C
I
TIMERUP
voltage
FILTER
) to equal I
TIMER
×
V
TIMERH
). If the excessive current persists
(
µ
SENSE
) F
is then charged up to the V
across
LIMIT
equal to 47mV. This feature
The nominal ovecurrent
for somewhat longer than
TIMER
R
SENSE
should be selected
TIMER
FLT
) for which the
exceeds
crosses the
CC
TIMER
pin and
(4)
) that
TIMERH
the
11
An initial value for C
will take for the MIC2586/MIC2586R to completely charge up
the output capacitive load. Assuming the load is enabled by
the PWRGDx (or /PWRGDx) signal(s) of the controller, the
turn-on delay time is derived from the following expression, I
= C × (dV/dt):
Using parametric values for the MIC2586/MIC2586R, an
expression relating a worse-case design value for C
using the MIC2586/MIC2586R specification limits, to the
circuit's turn-on delay time is:
For example, in a system with a C
V
buss of 1.65A, the nominal circuit design equations steps
are:
Allowing for capacitor tolerances and a nominal 36ms turn-on
time, an initial worse-case value for C
The closest standard ±5% tolerance capacitor value is 3.3µF
and would be a good initial starting value for prototyping.
Whenever the MIC2586 is not in current limit, C
discharged to GND by an internal 3.5µA current sink
(I
For the MIC2586R, the circuit breaker automatically resets
after (20) t
exists, capacitor C
threshold, and if exceeded, trip the circuit breaker. Capacitor
C
across C
time another start cycle is initiated. This will continue until
either of the following occurs:
removed,
TIMERDN
CC
TIMER
1. Choose I
2. Select an R
3. Using I
= +72V, and a maximum load current on a nominal +48V
C
t
TURN-ON
TIMER(MAX)
19.6mΩ);
on time is calculated using Equation 5:
C
C
C
will then be discharged by I
).
the time it takes to charge the total load capacitance.
TIMER(MAX)
TIMER(MAX)
TIMER
t
TURN-ON
TIMER
FLT_AUTO
=
b)
(MAX)
CHARGE
C
=
LOAD
drops below the V
LIMIT
=
0.036s
=
=
=
the
(
1000
t
TIMER
I
t
t
LIMIT
TURN
time constants. If the fault condition still
× V
TURN
TURN
= I
SENSE
= I
TIMER
CC(MAX)
HOT_SWAP(nom)
×
µ
-
-
input
-
2A
LIMIT
V
ON
ON
ON
will begin to charge up to the V
⎛
⎜
⎝
F × 72V
TIMERH(MIN
94
×
×
×
is found by calculating the time it
(Closest 1% standard value is
⎛
⎜
⎝
×
I
⎛
⎜
⎝
= 2A, the application circuit turn-
TIMERUP(MA
1.280V
94
120
10
)
supply
×
6 -
µ
10
= 36ms
)
sec
A
µ
LOAD
6 -
F
TIMERL
= 2A (1.65A + 20%);
a) the fault condition is
⎞
⎟
⎠
X)
sec
TIMERDN
⎞
⎟
⎠
µ
TIMER
=
F
= 1000µF, a maximum
MIC2586/MIC2586R
3.38
⎞
⎟
⎠
voltage
threshold, at which
is:
µ
until the voltage
F
[phone]
M9999-102204
power
TIMER
(5)
(6)
TIMERH
TIMER
is
is
,