MIC2588-2BM Micrel Inc, MIC2588-2BM Datasheet - Page 15
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MIC2588-2BM
Manufacturer Part Number
MIC2588-2BM
Description
IC CTRLR HOT SWAP NEG HV 8-SOIC
Manufacturer
Micrel Inc
Type
Hot-Swap Controllerr
Datasheet
1.MIC2588-1YM_TR.pdf
(21 pages)
Specifications of MIC2588-2BM
Applications
General Purpose
Internal Switch(s)
No
Voltage - Supply
-19 V ~ -80 V
Operating Temperature
-40°C ~ 85°C
Mounting Type
Surface Mount
Package / Case
8-SOIC (0.154", 3.90mm Width)
Family Name
MIC2588
Package Type
SOIC
Operating Supply Voltage (min)
-19V
Operating Supply Voltage (max)
-80V
Operating Temperature (min)
-40C
Operating Temperature (max)
85C
Operating Temperature Classification
Industrial
Product Depth (mm)
3.94mm
Product Height (mm)
1.48mm
Product Length (mm)
4.93mm
Mounting
Surface Mount
Pin Count
8
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
For systems that experience known load current surges
exceeding the 400µs internal overcurrent filter (t
RC circuit consisting of R6 and C6 provides a means for
additional overcurrent filtering to eliminate false “tripping”
of the circuit breaker due to these transient load current
surges. It is highly recommended to limit the increase of
the overcurrent filter to approximately 2x the internal filter to
allow the MOSFET to operate within its thermal specifica-
tions and SOA. R6 and C6 act as a low-pass filter to reduce
the slew rate of the SENSE pin voltage. The SENSE pin
current is nominally 200nA, resulting in a slight voltage drop
across R6 that will combine in series with the voltage across
R
V
to select component values for a given overcurrent filter
delay.
where V
in the electrical specifications, V(t0) is the voltage drop across
the sense resister before the short or overcurrent condition
occurs, and V(t) is the voltage drop across the sense resis-
tor when the short or overcurrent is applied. The following
example sets an overcurrent delay of 1ms for a 7.5A load
current surge with a 2A steady-state load current and 5A
current limit (R
Using Equation 8, for R6 = 2.7kΩ, C6 is 0.47µF.
The capacitor (C2) connected from UV to reference (V
is used as a glitch filter for the input undervoltage monitor.
C2 combines with the resistive network at the UV pin to
form an RC time constant to slow the UV pin voltage fall
time whenever the input voltage experiences a negative
(magnitude) transient. During start-up, the UV rise time will
also be affected by a longer RC time constant due to R1,
therefore, the output start cycle will be delayed until the UV
pin crosses its threshold.
The circuit in Figure 6 consisting of M2, R7, R8, and a digital
control signal, can be used to reset the controller after the
GATE (and output) turns off. Once the output has been
latched off, applying a low-high-low pulse on the GATE of M2
via the System Enable control can toggle the UV pin. System
Enable is a user defined signal referenced to V
Sense Resistor Selection
The sense resistor is nominally valued at:
where V
threshold voltage (50mV) and I
nal load current level necessary to trip the internal circuit
breaker.
To accommodate worse-case tolerances in the sense re-
sistor (for a ±1% initial tolerance, allow ±3% tolerance for
September 2005
MIC2588/MIC2594
TRIP
SENSE
V
V(t
V(t) = 7.5A × 10mΩ = 75mV
TRIP
t
R
OCDLY
0
SENSE(nom)
) = 2A × 10mΩ = 20mV
– (R6 × I
TRIP
to produce an effective circuit breaker trip voltage of
= 50mV
TRIP(TYP)
is the typical circuit breaker trip voltage specified
– (R × C) ln 1 –
SENSE
SENSE
I
is the typical (or nominal) circuit breaker
HOT_SWAP(nom)
V
). The following equation can be used
= 10mΩ).
TRIP(typ)
┌
└
│
V
HOT_SWAP(NOM)
V(t) – V(t
TRIP
– V(t
O
O
)
)
┌
│
└
EE
is the nomi-
.
FLT
), the
(8)
(9)
EE
)
15
variations over time and temperature) and circuit breaker
threshold voltages, a slightly more detailed calculation must
be used to determine the minimum and maximum hot swap
load currents.
As the MIC2588’s minimum current limit threshold voltage
is 40mV, the minimum hot swap load current is determined
where the sense resistor is 3% high:
Keep in mind that the minimum hot swap load current
should be greater than the application circuit’s upper
steady-state load current boundary. Once the lower value
of R
the maximum hot swap load current (I
the circuit may let pass in the case of tolerance build-up in
the opposite direction. Here, the worse case maximum is
found using a V
resistor 3% low in value:
In this case, the application circuit must be sturdy enough to
operate up to approximately 1.5x the steady-state hot swap
load current. For example, if an MIC2588 circuit must pass a
minimum hot swap load current of 4A without nuisance trips,
R
where the nearest 1% standard value is 10.0mΩ. At the
other tolerance extremes, I
question is then simply:
With a knowledge of the application circuit’s maximum
hot swap load current, the power dissipation rating of the
sense resistor can be determined using P = I
the current is I
R
Thus, the sense resistor’s maximum power dissipation is:
A 0.5W sense resistor is a good choice in this application.
Power MOSFET Selection
Selecting the proper external MOSFET for use with the-
MIC2588/MIC2594 involves three straightforward tasks:
Power MOSFET Operating Voltage Requirements
The first voltage requirement for the MOSFET is easily stated:
SENSE
SENSE(max)
P
I
I
R
I
MAX
•Choice of a MOSFET which meets minimum voltage
requirements.
•Selection of a device to handle the maximum continuous
current (steady-state thermal issues).
•Verify the selected part’s ability to withstand any peak
currents (transient thermal issues).
SENSE
HOT_SWAP(min)
HOT_SWAP(max)
HOT_SWAP(max)
SENSE(nom)
should be set to:
= (6.19A)
has been calculated, it is good practice to check
= (1.03)(R
HOT_SWAP(max)
TRIP(MAX)
2
40mV
× (10.3mΩ) = 0.395W
4A
1.03 × R
0.97 × R
61.9mV
10mΩ
SENSE(nom)
threshold of 60mV and a sense
40mV
60mV
10mΩ
HOT_SWAP(MAX)
SENSE(nom)
SENSE(nom)
= 6.19A and the resistance
6.19A
) = 10.3mΩ.
HOT_SWAP(MAX)
R
R
for the circuit in
38.8mV
61.9mV
SENSE(nom)
SENSE(nom)
2
M9999-083005
× R. Here,
) that
Micrel