參數(shù)資料
型號: MIC2594-2BM TR
廠商: Micrel Inc
文件頁數(shù): 12/21頁
文件大?。?/td> 1079K
描述: IC CTRLR HOT SWAP NEG HV 8-SOIC
標(biāo)準(zhǔn)包裝: 2,500
類型: 熱交換控制器
應(yīng)用: 通用
內(nèi)部開關(guān):
電源電壓: -19 V ~ -80 V
工作溫度: -40°C ~ 85°C
安裝類型: 表面貼裝
封裝/外殼: 8-SOIC(0.154",3.90mm 寬)
供應(yīng)商設(shè)備封裝: 8-SOIC
包裝: 帶卷 (TR)
其它名稱: MIC2594-2BMTR
MIC2594-2BMTR-ND
September 2005
12
M9999-083005
MIC2588/MIC2594
Micrel
subsequent DC/DC converter modules or for other system
uses as desired. When used as an enable signal, the time
necessary for the PWRGD (or /PWRGD) signal to pull-up
(when in high impedance state) will depend upon the load
(RC) that is present on this output.
Circuit Breaker Function
The MIC2588 and the MIC2594 employ an electronic circuit
breaker that protects the MOSFET and other system compo-
nents against faults such as short circuits. The current limit
threshold is set via an external resistor, R
SENSE
, connected
between the V
EE
 and SENSE pins and is determined by:
V
TRIP
R
SENSE
I
LIM
=
 
(3)
where V
TRIP
 is the circuit breaker trip threshold specied in
the Electrical Characteristics Table.
An internal 400祍 timer limits the length of time (t
FLT
) for
which the circuit can draw current in excess of its programmed
threshold before the circuit breaker is tripped. This short
delay prevents nuisance tripping of the circuit breaker due
to system transients while providing rapid protection against
large-scale transient faults. Whenever the voltage across
R
SENSE
  exceeds 50mV, two things happen:
1. A constant-current regulation loop is engaged and is
designed to hold the voltage across R
SENSE
 equal to
50mV. This protects both the load and the MIC2588
circuit from excessively high currents. This loop will
engage in less than 1祍 from the time at which the
overvoltage condition on R
SENSE
occurs.
2. The internal 400祍 timer is started. If the 400祍
timeout period expires, the circuit breaker trips
and the GATE pin is immediately pulled low by an
internal current pull-down. This operation turns off
the MOSFET quickly and disconnects the input
from the load.
Undervoltage/Overvoltage DetectionMIC2588
The MIC2588 has UV and OV input pins. These pins can be
used to detect input supply rail undervoltage and overvoltage
conditions. Undervoltage lockout prevents energizing the load
until the supply input is stable and within tolerance. In a similar
fashion, overvoltage turn-off prevents damage to sensitive
circuit components should the input voltage exceed normal
operational limits. Each of these pins is internally connected
to an analog comparator with 20mV of hysteresis. When the
UV pin falls below its V
UVL
 threshold or the OV pin is above
its V
OVH
threshold, the GATE pin is immediately pulled low.
The GATE pin will be held low until UV exceeds its V
UVH
threshold or OV drops below its V
OVL
threshold. The UV
and OV circuits threshold trip points are programmed using
the resistor divider R1, R2, and R3 as shown in the Typical
Application. The equations to set the trip points are shown
below. For the following example, the circuits nominal UV
threshold is set to V
UV
 = 37V and the nominal OV threshold
is placed at V
OV
 = 72V, values commonly used in Central
Ofce power distribution applications.
V
V    (typ)
R1+R2 +R3
R2+R3
V
V    (typ)
R1+R2 +R3
R3
UV
UVL
OV
OVH
=
?/DIV>
(
)
(
)
=
?/DIV>
(
)
 
(4)
 
 
(5)
Given V
UV
, V
OV
, and any one resistor value, the remaining
two resistor values can be found. A suggested value for R3
is that which will provide a minimum of 100礎(chǔ) of current
through the voltage divider chain at V
DD
 = V
UV
. This yields
the following as a starting point:
 
R3
V    (typ)
100 A
12.23k
OVH
=
m
=
W
The closest standard 1% value for R3 = 12.4k? Using Equa-
tions 3 and 4 above, solving for R2 and R1 yields:
 
R2  R3
V
V
 1
R2  12.4k
72V
37V
 1
R2  11.729k
OV
UV
=    ?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
W ?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
W
The closest standard 1% value for R2 = 11.8k? Next, the
value for R1 is calculated:
 
R1  R3
V    1.223V
1.223V
 R2
R1  12.4k
72V  1.223V
1.223V
 11.8k&
R1  705.808k
OV
=    ?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
W ?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
=
W
The closest standard 1% value for R1 = 698k?
Using standard 1% resistor values, the circuits nominal
UV and OV thresholds are:
    V
UV
 = 36.5V
    V
OV
 = 71.2V
Good general engineering design practices must consider
the tolerances associated with these parameters, including
but not limited to, power supply tolerance, undervoltgae
and overvoltage tolerances, and the tolerances of the
external passive components.
Programmable UVLO HysteresisMIC2594
The MIC2594 has user-programmable hysteresis by means
of the ON and OFF pins. This allows setting the part to turn
on at a voltage V1, and not turn off until a second voltage
V2, where V2 < V1. This can signicantly simplify dealing
with source impedances in the supply bus while at the same
time increasing the amount of available operating time from
a loosely regulated power supply (for example, a battery
supply). Similarly to the MIC2588, each of these pins is
internally connected to an analog comparator with 20mV of
hysteresis. The MIC2594 holds the output off until the voltage
at the ON pin exceeds its V
ONH
 threshold value given in the
Electrical Characteristics table. Once the output has been
enabled by the ON pin, it will remain on until the voltage at
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