參數(shù)資料
型號(hào)： MIC2595-2BM
廠商： MICREL INC
元件分類： 電源管理
英文描述： Replaced by PTH05060W :
中文描述： 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO14
封裝： SOIC-14
文件頁(yè)數(shù)： 13/17頁(yè)
文件大?。?/td> 100K
代理商： MIC2595-2BM
March 2004
13
M9999-031504
MIC2589/2595
Micrel
To accommodate worst-case tolerances in the sense resistor
(for a
±
1% initial tolerance, allow
±
3% tolerance for 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 cur-
rents.
As the MIC2589/95
’
s minimum current-limit threshold volt-
age is 40mV, the minimum hot swap load current is deter-
mined where the sense resistor is 3% high:
I
(min)
40mV
1.03 R
(nom)
38.8mV
R
(nom)
HOT_SWAP
SENSE
SENSE
=
=
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
SENSE
has
been calculated, it is good practice to check the maximum hot
swap load current (I
HOT_SWAP
(max)) which the circuit may let
pass in the case of tolerance build-up in the opposite direc-
tion. Here, the worst-case maximum is found using a
V
TRIP
(max) of 60mV and a sense resistor 3% low in value:
60mV
0.97 R
SENSE
In this case, the application circuit must be sturdy enough to
operate over an ~1.6-to-1 range in hot swap load currents.
For example, if an MIC2595 circuit must pass a minimum hot
swap load current of 4A without nuisance trips, R
SENSE
should be set to
38.8mV
4A
standard value is 9.76m
. At the other tolerance extremes,
I
HOT_SWAP
(max) for the circuit in question is then simply:
61.9mV
9.76m
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
2
×
R. Here, The I is
I
HOT_SWAP
(max) = 6.3A and the R is R
SENSE
(min) =
(0.97)(R
SENSE
(nom)) = 9.47m
. Thus, the sense resistor
’
s
maximum power dissipation is:
P
MAX
= (6.3A)
2
×
(9.47m
) = 0.376W
A 0.5
sense resistor is a good choice in this application.
No-Load Detection
For those applications in which a minimum load current will
always be present, the no-load detect capability of the
MIC2589/89R/95/95R family offers system designer the abil-
ity to perform a shutdown operation on such fault conditions,
such as an unscheduled or unexpected removal of PC boards
from the system or on-board fuse failure.
As long as the minimum current drawn by the load is at least
I
(max)
(nom)
61.9mV
R
(nom)
HOT_SWAP
SENSE
=
=
9.7m
=
, and the nearest 1%
I
(max)
6.3A
HOT_SWAP
=
20% of the maximum output current (defined by
V
SENSE
),
R
TRIP
the output of the hot swap controllers will remain enabled. If
the output current falls below 12% of the maximum output
current, the controller
’
s no-load detection loop is enabled. In
this loop, an internal current source, I
CNLD
, will charge an
external capacitor C
NLD
. An expression for the controller
’
s
no-load time-out delay is given by:
t
V
C
I
CNLD
NLD
CNLD
NLD
=
×
where V
CNLD
= 1.24V (typ); I
CNLD
= 25
μ
A (typ); and C
NLD
is
an external capacitor connected from Pin 6 to V
EE
. Once the
voltage on C
NLD
reaches its no-load threshold voltage, V
CNLD
,
the loop times out and the controller will shut down until it is
reset manually (MIC2589/95) or until it performs an auto-retry
operation (MIC2589R/95R).
Undervoltage/Overvoltage Detection (MIC2589 and
MIC2589R)
The MIC2589 and the MIC2589R have
“
UV
”
and
“
OV
”
input
pins that 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 turnoff prevents
damage to sensitive circuit components should the input
voltage exceed normal operational limits. Each of these pins
is internally connected to analog comparators 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
the UV pin is above its V
UVH
threshold or the OV pin is below
its V
OVL
threshold. The circuit
’
s UV and OV threshold voltage
levels are programmed using the resistor divider R1, R2, and
R3 as shown in the
“
Typical Application
”
where the equations
to set the trip points are shown below. For the following
example, the circuit
’
s UV threshold is set to V
UV
= 37V and the
OV threshold is set at V
OV
= 72V, values commonly used in
Central Office power distribution applications.
V
V
(typ)
R1 R2 R3
R2 R3
(
V
V
(typ)
R1 R2 R3
R3
UV
UVL
OV
OVH
=
×
(
)
)
=
×
(
)
Given V
UV
, V
OV
, and any one resistor value, the remaining
two resistor values can be determined. A suggested value for
R3 is that which will provide approximately 100
μ
A 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
1.223V
100 A
12.23k
OVH
=
=
The closest standard 1% value for R3 = 12.4k
. Solving for
R2 and R1 yields:
相關(guān)PDF資料
PDF描述
MIC2589R-1BM SINGLE-CHANNEL NEGATIVE HIGH VOLTAGE HOT SWAP POWER CONTROLLERS/SEQUENCERS
MIC2753-RBM5 Power Supply Supervisors Preliminary Information
MIC2753-SBM5 Power Supply Supervisors Preliminary Information
MIC2754-LBM5 Power Supply Supervisors Preliminary Information
MIC2754-RBM5 Power Supply Supervisors Preliminary Information
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