MIC2588 [MICREL]
Single-Channel, Negative High-Voltage Hot Swap Power Controllers; 单通道，负高压热插拔电源控制器
| 型号： | MIC2588 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | Single-Channel, Negative High-Voltage Hot Swap Power Controllers |
| 文件： | 总14页 (文件大小：84K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC2588/MIC2594
Single-Channel, Negative High-Voltage Hot
Swap Power Controllers
General Description
Features
The MIC2588 and the MIC2594 are single-channel, nega-
tive-voltage hot swap controllers designed to address the
needforsafeinsertionandremovalofcircuitboardsinto“live”
high-voltage system backplanes, while using very few exter-
nal components. The MIC2588 and the MIC2594 are each
available in an 8-pin SOIC package and work in conjunction
withanexternalN-ChannelMOSFETforwhichthegatedrive
is controlled to provide inrush current limiting and output
voltage slew-rate control. Overcurrent fault protection is also
provided for which the overcurrent threshold is program-
mable. During an output overload condition, a constant-
current regulation loop is engaged to ensure that the system
power supply maintains regulation. If a fault condition ex-
ceeds a built-in 400µs nuisance-trip delay, the MIC2588 and
the MIC2594 will latch the circuit breaker’s output off and will
remain in the off state until reset by cycling either the UV/OFF
pin or the power to the IC. A master Power-Good signal is
provided to indicate that the output voltage of the soft-start
circuit is within its valid output range. This signal can be used
to enable one or more DC-DC converter modules.
• MIC2588:
Pin-for-pin functional equivalent to the
LT1640/LT1640A/LT4250
• Provides safe insertion and removal from live –48V
(nominal) backplanes
• Operates from –19V to –80V
• Electronic circuit breaker function
• Built-in 400µs “nuisance-trip” delay (t
• Regulated maximum output current into faults
• Programmable inrush current limiting
• Fast response to short circuit conditions (< 1µs)
• Programmable undervoltage and overvoltage lockouts
(MIC2588-xBM)
)
FLT
• Programmable UVLO hysteresis (MIC2594-xBM)
• Fault reporting:
Active-HIGH (-1BM) and Active-LOW
(-2BM) Power-Good signal output
Applications
• Central office switching
• –48V power distribution
• Distributed power systems
All support documentation can be found on Micrel’s web
site at www.micrel.com.
Typical Application
–
48V
RETURN
(Long Pin)
–
48V
MIC2588-2BM
RETURN
(Short Pin)
R1
698kΩ
1%
8
DC-DC Converter
IN+ OUT+
/ON/OFF
VDD
+5VOUT
3
2
1
7
UV
OV
/PWRGD
DRAIN
R2
11.8kΩ
1%
5V
RETURN
IN–
OUT
–
VEE
SENSE
GATE
4
5
6
CFDBK
R3
12.4kΩ
1%
RFDBK
CGATE
R4
M1
0.1µF 100µF
–
48V
INPUT
(Long Pin)
RSENSE
Input Overvoltage = 71.2V
Input Undervoltage = 36.5V
(See "Functional Description" for more detail)
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
M9999-122303
December 2003
1
MIC2588/MIC2594
Micrel
Ordering Information
Part Number
PWRGD
Polarity
Lockout Functions
Circuit Breaker
Function
Package
MIC2588-1BM
MIC2588-2BM
MIC2594-1BM
MIC2594-2BM
Active-High
Active-Low
Active-High
Active-Low
Undervoltage and Overvoltage
Undervoltage and Overvoltage
Programmable UVLO Hysteresis
Programmable UVLO Hysteresis
Latched Off
Latched Off
Latched Off
Latched Off
8-pin SOIC
8-pin SOIC
8-pin SOIC
8-pin SOIC
Pin Configuration
PWRGD
OV
1
2
3
4
8
7
6
5
VDD
DRAIN
/PWRGD
1
2
3
4
8
7
6
5
VDD
OV
UV
DRAIN
GATE
UV
GATE
VEE
SENSE
VEE
SENSE
8-Pin SOIC (M)
MIC2588-1BM
8-Pin SOIC (M)
MIC2588-2BM
PWRGD
ON
1
2
3
4
8
7
6
5
VDD
/PWRGD
ON
1
2
3
4
8
7
6
5
VDD
DRAIN
GATE
SENSE
DRAIN
GATE
SENSE
OFF
OFF
VEE
VEE
8-Pin SOIC (M)
MIC2594-1BM
8-Pin SOIC (M)
MIC2594-2BM
M9999-122303
2
December 2003
MIC2588/MIC2594
Pin Description
Pin Number
Micrel
Pin Name
Pin Function
PWRGD
/PWRGD
Power-Good Output: Open-drain. Asserted when the voltage on the DRAIN
pin (VDRAIN) is within VPGTH of VEE, indicating that the output voltage is
within proper specifications.
1
1
1
2
2
3
MIC25XX-1
PWRGD
Active-High
MIC2588-1 and MIC2594-1: PWRGD will be high-impedance when
V
DRAIN is less than VPGTH, and will pull-down to VDRAIN when VDRAIN is
greater than VPGTH. Asserted State: Open-Drain.
MIC25XX-2
/PWRGD
Active-Low
MIC2588-2 and MIC2594-2: /PWRGD will pull-down to VDRAIN when
VDRAIN is less than VPGTH, and will be high impedance when VDRAIN is
greater than VPGTH. Asserted State: Active-Low.
OV
Threshold
MIC2588: Overvoltage Threshold Input. When the voltage at the OV pin is
greater than the VOVH threshold, the GATE pin is immediately pulled low by an
internal 100µA current pull-down.
ON
MIC2594: Turn-On Threshold. At initial system power-up or after the device
has been shut off by the OFF pin, the voltage on the ON pin must exceed
the VONH threshold in order for the MIC2594 to be enabled.
Turn-On Threshold
UV
Threshold
MIC2588: Undervoltage Threshold Input. When the voltage at the UV pin is
less than the VUVL threshold, the GATE pin is immediately pulled low by an
internal 100µA current pull-down. The UV pin is also used to cycle the device
off and on to reset the circuit breaker. Taken together, the OV and UV pins
form a window comparator which defines the limits of VEE within which the
load may safely be powered.
OFF
MIC2594: Turn-Off Threshold. When the voltage at the OFF pin is less than
the VOFFL threshold, the GATE pin is immediately pulled low by an internal
100µA current pull-down. The OFF pin is also used to cycle the device off and
on to reset the circuit breaker. Taken together, the ON and OFF pins provide
programmable hysteresis for the turn-on command voltage.
3
Turn-Off Threshold
4
5
VEE
Negative Supply Voltage Input.
SENSE
Circuit Breaker Sense Input: The current-limit threshold is set by connecting
a resistor between this pin and VEE. When the current-limit threshold of
IR = 50mV is exceeded for an internal delay tFLT (400µs), the circuit breaker
is tripped and the GATE pin is immediately pulled low. Toggling UV or OV
will reset the circuit breaker. To disable the circuit breaker, externally
connect SENSE and VEE together.
6
7
8
GATE
DRAIN
VDD
Gate Drive Output: Connect to the gate of an external N-Channel MOSFET.
Drain Sense Input: Connect to the drain of an external N-Channel MOSFET.
Positive Supply Input.
December 2003
3
M9999-122303
MIC2588/MIC2594
Micrel
Absolute Maximum Ratings(1)
Operating Ratings(2)
(All voltages are referred to V
)
Supply Voltage (V – V ) .......................... +19V to +80V
EE
DD
EE
Supply Voltage (V – V ) ......................... –0.3V to 100V
Ambient Temperature Range (T ) ............... –40°C to 85°C
DD
EE
A
DRAIN, PWRGD pins................................... –0.3V to 100V
GATE pin..................................................... –0.3V to 12.5V
SENSE, OV, UV, ON, OFF pins....................... –0.3V to 6V
Junction Temperature (T ) ........................................ 125°C
J
Package Thermal Resistance
SOIC (θ ) .........................................................152°C/W
JA
(3)
ESD Ratings
Human Body Model................................................... 2kV
Soldering
Vapor Phase .......................... (60 sec.) +220°C +5 ±0°C
Infrared ................................... (15 sec.) +235°C +5 ±0°C
DC Electrical Characteristics(4)
VDD = 48V, VEE = 0V, TA = 25°C, unless otherwise noted. Bold indicates specifications apply over the full operating temperature range of
–40°C to +85°C.
Symbol
VDD – VEE
IDD
Parameter
Condition
Min
19
Typ
Max
80
5
Units
Supply Voltage
Supply Current
3
mA
mV
µA
VTRIP
Circuit Breaker Trip Voltage
GATE Pin Pull-up Current
VTRIP = VSENSE – VEE
40
30
50
45
60
60
IGATEON
VGATE = VEE to 8V
19V ≤ (VDD – VEE) ≤ 80V
IGATEOFF
GATE Pin Sink Current
(VSENSE – VEE) = 100mV
VGATE = 2V
100
230
mA
VGATE
ISENSE
VUVH
GATE Drive Voltage, (VGATE – VEE
)
15V ≤ (VDD – VEE) ≤ 80V
VSENSE = 50mV
9
10
0.2
11
V
µA
V
SENSE Pin Current
UV Pin High Threshold Voltage
UV Pin Low Threshold Voltage
UV Pin Hysteresis
Low-to-High Transition
High-to-Low Transition
1.213
1.198
1.243
1.223
20
1.272
1.247
VUVL
V
VUVHYS
VOVH
mV
V
OV Pin High Threshold Voltage
OV Pin Low Threshold Voltage
OV Pin Hysteresis
Low-to-High Transition
High-to-Low Transition
1.198
1.165
1.223
1.203
20
1.247
1.232
VOVL
V
VOVHYS
VONH
mV
V
ANSI ON Pin High Threshold
Voltage
Low-to-High Transition
High-to-Low Transition
VUV = 1.25V
1.198
1.198
1.223
1.247
1.247
0.5
VOFFH
ICNTRL
VPGTH
VOLPG
ANSI OFF Pin Low Threshold
Voltage
1.223
1.26
V
µA
V
Input Bias Current
(OV, UV, ON, OFF Pins)
Power-Good Threshold
High-to-Low Transition
1.1
1.40
(VDRAIN – VEE
)
PWRGD Output Voltage
VOLPG – VDRAIN
(relative to voltage at the DRAIN pin) 0mA ≤ IPG(LOW) ≤ 1mA
MIC25XX-1
(VDRAIN – VEE) < VPGTH
(VDRAIN – VEE) > VPGTH
VPWRGD = VDD = 80V
–0.25
–0.25
0.8
0.8
1
V
V
MIC25XX-2
ILKG(PG)
PWRGD Output Leakage Current
µA
Notes:
1. Exceeding the “Absolute Maximum Ratings” may damage the devices.
2. The devices are not guaranteed to function outside the specified operating conditions.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF. Machine model: 200pF, no series
resistance.
4. Specification for packaged product only.
M9999-122303
4
December 2003
MIC2588/MIC2594
Micrel
AC Electrical Characteristics(5)
Symbol
Parameter
Condition
Note 6
Min
Typ
Max
Units
tFLT
Built-in Overcurrent Nuisance Trip
Time Delay (Figure 1)
400
µs
tOCSENSE
Overcurrent Sense to GATE Low
(Figure 2)
VSENSE – VEE = 100mV
3.5
µs
tOVPHL
tOVPLH
tUVPHL
tUVPLH
tPGL(1)
OV to GATE Low (Figure 3)
OV to GATE High (Figure 3)
UV to GATE Low (Figure 4)
UV to GATE High (Figure 4)
Note 6
Note 6
Note 6
Note 6
1
1
1
1
1
µs
µs
µs
µs
µs
DRAIN High to PWRGD Output Low RPULLUP = 100kΩ, CLOAD on PWRGD = 50pF(6)
(-1 Version parts only)
tPGL(2)
tPGH(1)
tPGH(2)
DRAIN Low to /PWRGD Output Low RPULLUP = 100kΩ, CLOAD on /PWRGD = 50pF(6)
(-2 Version parts only)
1
2
2
µs
µs
µs
DRAIN Low to PWRGD Output High RPULLUP = 100kΩ, CLOAD on PWRGD = 50pF(6)
(-1 Version parts only)
DRAIN High to /PWRGD Output High RPULLUP = 100kΩ, CLOAD on /PWRGD = 50pF(6)
(-2 Version parts only)
Notes:
5. Specification for packaged product only.
6. Not 100% production tested. Parameters are guaranteed by design.
Test Circuit
[Section under construction]
December 2003
5
M9999-122303
MIC2588/MIC2594
Micrel
Typical Characteristics
[Section under construction]
MICx xxx
vs. xxx
MICx xxx
vs. xxx
MICx xxx
vs. xxx
10
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
2
2
2
2
4
6
8
8
8
8
10
10
10
10
0
0
0
0
2
2
2
2
4
6
8
8
8
8
10
10
10
10
0
0
0
0
2
2
2
2
4
6
8
8
8
8
10
10
10
10
XXX (X)
XXX (X)
XXX (X)
MICx xxx
vs. xxx
MICx xxx
vs. xxx
MICx xxx
vs. xxx
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
4
6
4
6
4
6
XXX (X)
XXX (X)
XXX (X)
MICx xxx
vs. xxx
MICx xxx
vs. xxx
MICx xxx
vs. xxx
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
4
6
4
6
4
6
XXX (X)
XXX (X)
XXX (X)
MICx xxx
vs. xxx
MICx xxx
vs. xxx
MICx xxx
vs. xxx
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
10
9
8
7
6
5
4
3
2
1
0
4
6
4
6
4
6
XXX (X)
XXX (X)
XXX (X)
M9999-122303
6
December 2003
MIC2588/MIC2594
Micrel
Timing Diagrams
OVERCURRENT
EVENT
t < tFLT
t ≥ tFLT
ILIMIT
ILOAD
0A
Output OFF
(at VDD
Load current is regulated
at ILIMIT = 50mV/RSENSE
)
VDRAIN
(at VEE
)
(at VEE)
VGATE
(VEE +10V)
Reduction in VDRAIN to support
LIMIT = 50mV/RSENSE
(at VEE
)
I
Figure 1. Overcurrent Response
100mV
tOCSENSE
1V
VSENSE - VEE
VGATE
Figure 2. SENSE to GATE LOW Timing Response
1.223V
1.203V
VOV
tOVPHL
tOVPLH
VGATE
1V
1V
Figure 3. Overvoltage Response
December 2003
7
M9999-122303
MIC2588/MIC2594
Micrel
VUV
1.223V
1.243V
tUVPHL
tUVPLH
VGATE
1V
1V
Figure 4. Undervoltage Response
MIC2588/94-1
VDRAIN
VPGTH
VPGTH
tPGL1
VEE
tPGH1
PWRGD not asserted
VPWRGD — VDRAIN = 0V
PWRGD asserted - High Impedance
PWRGD not asserted
VPWRGD — VDRAIN = 0V
PWRGD
VEE
MIC2588/94-2
VDRAIN
VPGTH
VPGTH
tPGH2
VEE
tPGL2
/PWRGD
VEE
Figure 5. DRAIN to Power-Good Response
M9999-122303
8
December 2003
MIC2588/MIC2594
Micrel
Functional Diagram
VDD1
Internal VDD
and
VDD1
VDD
45µA
Reference
Generator
VREF1
GATE
SENSE
+
100µA
–
VEE
Current
Limit
State
VEE
50mV
VEE
VDD1
PWRGD
Nuisance
Trip Filter
(400µs)
VEE
/PWRGD
Logic +
Circuit
Breaker
UV
–
EN
+
VTH(UV/OV)
VEE
–
+
OV
6V
Clamp
–
DRAIN
+
VPGTH
Internal
PG
For Power Good circuitry only
denotes -2 option
MIC2588 Block Diagram
December 2003
9
M9999-122303
MIC2588/MIC2594
Micrel
C
and R
prevent turn-on and hot swap current
Functional Description
Hot Swap Insertion
GATE
FDBK
surges which would otherwise be caused by (C
+
FDBK
C
) coupling turn-on transients from the drain to the
D-G(M1)
When circuit boards are inserted into systems carrying live
supply voltages (“hot swapped”), high inrush currents often
result due to the charging of bulk capacitance that resides
across the circuit board’s supply pins. These current spikes
can cause the system’s supply voltages to temporarily go out
of regulation, causing data loss or system lock-up. In more
extreme cases, the transients occurring during a hot swap
event may cause permanent damage to connectors or on-
board components.
gate of M1. An appropriate value for C
mined using the formula for a capacitive voltage divider:
may be deter-
GATE
Maximum voltage on C at turn-on must be less than
GATE
V
of M1:
THRESHOLD
1. For a standard 10V enhancement N-Channel
MOSFET, V is about 4.25V.
THRESHOLD
2. Choose 3.5V as a safe maximum voltage to safely
avoid turn-on transients.
V
× [C
+ (C
+ C
D-G(M1)
)]
The MIC2588 and the MIC2594 are designed to address
theseissuesbylimitingthemagnitudeofthetransientcurrent
during hot swap events. This is achieved by controlling the
rate at which power is applied to the circuit board (di/dt and
dv/dt management). In addition, to inrush current control, the
MIC2588 and the MIC2594 incorporate input voltage super-
visoryfunctionsandcurrentlimiting, therebyprovidingrobust
protection for both the system and the circuit board.
G-S(M1)
GATE
FDBK
= [(V – V (min)) × (C
+ C
)]
DD
EE
FDBK
D-G(M1)
V
× C
= [(V – V (min)) – V
] × (C
+ C
)
G-S(M1)
GATE
DD
EE
G-S(M1)
FDBK
D-G(M1)
V
DD – VEE(min) – V
(
)
G-S(M1)
CGATE = C
+ CD−G(Q1)
×
(
)
(2)
FDBK
VG-S(M1)
Start-Up Cycle
While the value for R
is not critical, it should be chosen
FDBK
When the input voltage to the IC is between the overvoltage
and undervoltage thresholds (MIC2588) or is greater than
to allow a maximum of several milliamperes to flow in the
gate-drain circuit of M1 during turn-on. While the final value
V
(MIC2594), a start cycle is initiated. At this time, the
for R
R
is determined empirically, initial values between
= 15kΩ to 27kΩ for systems with a maximum value of
ON
FDBK
GATE pin of the IC applies a constant charging current
(I ) to the gate of the external MOSFET (M1). C
FDBK
75V for (V – V (min)) are appropriate.
GATEON
FDBK
DD
EE
creates a Miller integrator out of the MOSFET circuit, which
limits the slew-rate of the voltage at the drain of M1. The drain
voltage rate-of-change (dv/dt) of M1 is:
Resistor R4, in series with the MOSFETs gate, minimizes the
potential for parasitic high frequency oscillations from occur-
ring in M1. While the exact value of R4 is not critical,
commonly used values for R4 range from 10Ω to 33Ω.
I
dv M1
I
(
)
=
GATE(–)
DRAIN
GATEON
= –
For example, let us assume a hot swap controller is required
to maintain the inrush current into a 150µF load capacitance
at 1.7A maximum, and that this circuit may operate from
supply voltages as high as (V – V ) = 75V. The MOSFET
dt
C
C
FDBK
FDBK
where I
= Gate Charging Current = I
;
GATEON
GATE(+)
DD
EE
I
–I
, due to the extremely high
GATE(–)
GATE(+)
to be used with the MIC2588/94 is an IRF540NS 100V
transconductance values of power MOSFETs; and
2
D PAK device which has a typical (C ) of 250pF.
D-G
dv M1
Calculating a value for C
using Equation 1 yields:
(
)
DRAIN
FBDK
I
= C
×
GATE(–)
FDBK
dt
150µF × 45µA
C
=
= 3.97nF
FDBK
Relating the above to the maximum transient current into the
load capacitance to be charged upon hot swap or power-up
involves a simple extension of the same formula:
1.7A
Good engineering practice suggests the use of the worst-
case parameter values for I
from the “DC Electrical
GATEON
Characteristics” section:
C
× dv M1
DRAIN
(
)
LOAD
150µF × 60µA
I
=
CFDBK
=
= 5.3nF
CHARGE
dt
1.7A
where the nearest standard 5% value is 5.6nF. Substituting
5.6nF into Equation 2 from above yields:
I
GATEON
I
= C
× –
CHARGE
LOAD
C
FDBK
75V – 3.5V
(
)
= 0.12µF
C
= 5.6nF + 250pF ×
(
)
GATE
3.5V
C
×I
LOAD
GATEON
| I
| =
CHARGE
Finally, choosing R4 = 10Ω and R
= 20kΩ will yield a
C
FDBK
FDBK
suitable, initial design for prototyping.
Transposing:
C
×I
LOAD
GATEON
C
=
FDBK
(1)
| I
|
CHARGE
M9999-122303
10
December 2003
MIC2588/MIC2594
Micrel
Power-Good (PWRGD or /PWRGD) Output
Toaccommodateworst-casetolerancesinthesenseresistor
(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
currents.
For the MIC2588-1 and the MIC2594-1, the Power-Good
output signal (PWRGD) will be high impedance when V
DRAIN
when
drops below V
, and will pull down to V
PGTH
DRAIN
V
is above V
. For the MIC2588-2 and the
DRAIN
PGTH
MIC2594-2, /PWRGD will pull down to the potential of the
V
pin when V
drops below V
, and will be high
AstheMIC2588/94’sminimumcurrentlimitthresholdvoltage
is 40mV, the minimum hot swap load current is determined
where the sense resistor is 3% high:
DRAIN
DRAIN
PGTH
impedancewhenV
isaboveV . Hence, the-1parts
PGTH
DRAIN
have an active-high PWRGD signal and the -2 parts have an
active-low/PWRGDoutput. EitherPWRGDor/PWRGDmay
be used as an enable signal for one or more 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.
40mV
1.03 ×R
38.8mV
(nom)
I
(min) =
=
HOT_SWAP
R
(nom)
(
)
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
has
SENSE
beencalculated, itisgoodpracticetocheckthemaximumhot
swaploadcurrent(I (max))whichthecircuitmaylet
Circuit Breaker Function
HOT_SWAP
pass in the case of tolerance build-up in the opposite direc-
tion. Here, the worst-case maximum is found using a
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
V
(max) of 60mV and a sense resistor, 3% low in value:
TRIP
threshold is set via an external resistor, R
, connected
SENSE
60mV
0.97 ×R
61.9mV
(nom)
I
(max) =
=
between the V and SENSE pins. An internal 400µs timer
HOT_SWAP
EE
R
(nom)
(
)
SENSE
SENSE
limits the length of time (t ) for which the circuit can draw
FLT
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
providingrapidprotectionagainstlarge-scaletransientfaults.
In this case, the application circuit must be sturdy enough to
operate over a ~1.6-to-1 range in hot swap load currents. For
example, if an MIC2594 circuit must pass a minimum hot
swap load current of 4A without nuisance trips, R
SENSE
Whenever the voltage across R
things happen:
exceeds 50mV, two
SENSE
38.8mV
= 9.7mΩ
should be set to
, and the nearest 1%
4A
standard value is 9.76mΩ. At the other tolerance extremes,
1. A constant-current regulation loop is engaged de-
signed to hold the voltage across R equal to
SENSE
I
(max) for the circuit in question is then simply
HOT_SWAP
50mV. This protects both the load and the MIC2588
circuit from excessively high currents. This loop will
engage in less than 1µs from the time at which the
61.9mV
I
(max) =
= 6.3A
HOT_SWAP
9.76mΩ
overvoltage condition on R
occurs.
SENSE
With a knowledge of the application circuit’s maximum hot
2. The internal 400µs timer is started. If the 400µs
timeout period is exceeded, the circuit breaker trips
and the GATE pin is immediately pulled low by an
internal current pull-down. This operation turns off
theMOSFETquicklyanddisconnectstheinputfrom
the load.
swap load current, the power dissipation rating of the sense
resistor can be determined using P = I × R. Here, the I is
2
I
(max) = 6.3A and the R is R
(min) =
HOT_SWAP
SENSE
(0.97)(R
(nom)) = 9.47mΩ. Thus, the sense resistor’s
SENSE
maximum power dissipation is:
2
P
= (6.3A) × (9.47mΩ) = 0.376W
MAX
Current Sensing
A 0.5Ω sense resistor is a good choice in this application.
Undervoltage/Overvoltage Detection—MIC2588
As mentioned before, the MIC2588 and the MIC2594 employ
an external low-value resistor in series with the source of the
external MOSFET to measure the current flowing into the
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
load. The V connection to the IC from the negative supply
EE
is also one input to the part’s internal current sensing circuits
and the SENSE input is the other input.
Sense Resistor Selection
The sense resistor is nominally valued at:
VTRIP(typ)
RSENSE(nom) =
pinfallsbelowitsV
thresholdortheOVpinisaboveitsV
UVL
OVH
IHOT_SWAP(nom)
threshold, the GATE pin is immediately pulled low. The GATE
pin will be held low until UV exceeds its V threshold or OV
where V
(typ) is the nominal circuit breaker threshold
UVH
TRIP
drops below its V
threshold. The UV and OV circuit’s
voltage (= 50mV) and I
(nom) is the nominal hot
OVL
HOT_SWAP
threshold trip points are programmed using the resistor divider
swaploadcurrentleveltotriptheinternalcircuitbreakerinthe
application.
December 2003
11
M9999-122303
MIC2588/MIC2594
Micrel
R1, R2, and R3 as shown in the “Typical Application.” The
equations to set the trip points are shown below. For the
analog comparator with 20mV of hysteresis. The MIC2594
holds the output off until the voltage at the ON pin exceeds its
followingexample, thecircuit’sUVthresholdissettoV =37V
V
threshold value given in the “Electrical Characteristics”
UV
ONH
andtheOVthresholdisplacedatV =72V, valuescommonly
table. Once the output has been enabled by the ON pin, it will
OV
used in Central Office power distribution applications.
remain on until the voltage at the OFF pin falls below its V
OFFL
thresholdvalue, orthepartturnsoffduetoafault. Shouldeither
event occur, the GATE pin is immediately pulled low and will
R1+R2+R3
(
)
V
= V
(typ)×
(typ)×
UV
UVL
remain low until the ON pin once again exceeds its V
R2+R3
(
)
ONH
threshold. The circuit’s turn-on and turn-off points are set using
the resistor divider R1, R2, and R3 as shown in the “Typical
Application.” The equations to establish the trip points are
shown below. In the following example, the circuit’s ON thresh-
old is set to V = 40V and the circuit’s OFF threshold is V
R1+R2+R3
(
)
V
= V
OVH
OV
R3
Given V , V , and any one resistor value, the remaining
ON
OFF
UV
OV
= 35V.
two resistor values can be found. A suggested value for R3
is that which will provide approximately 100µA of current
throughthevoltagedividerchainatV =V .Thisyieldsthe
R1+R2 +R3
(
(typ)×
ONH
)
DD
UV
V
= V
ON
following as a starting point:
R3
V
(typ)
OVH
R1+R2 +R3
(
(typ)×
OFFL
)
R3 =
= 12.23kΩ
V
= V
100µA
OFF
R2 +R3
(
)
The closest standard 1% value for R3 = 12.4kΩ. Solving for
R2 and R1 yields:
Given V
, V , and any one resistor value, the remaining
two resistor values can be readily found. A suggested value
OFF ON
for R3 is that which will provide approximately 100µA of
V
OV
current through the voltage divider chain at V = V
. This
R2 = R3 ×
–1
DD
OFF
V
yields the following as a starting point:
UV
V
(typ)
OFFL
R3 =
= 12.23kΩ
72V
37V
100µA
R2 = 12.4kΩ ×
R2 = 11.729kΩ
–1
The closest standard 1% value for R3 = 12.4kΩ.
Then, solving for R2 and R1 yields:
The closest standard 1% value for R2 = 11.8kΩ. Next, the
value for R1 is calculated:
V
ON
R2 =R3 ×
–1
V
OFF
VOV –1.223V
R1= R3 ×
–R2
40V
1.223V
R2 =12.4kΩ ×
R2 =1.771kΩ
–1
35V
72V –1.223V
R1= 12.4kΩ ×
–R2
1.223V
The closest standard 1% value for R2 = 1.78kΩ.
R1= 705.808kΩ
V
–1.223V
The closest standard 1% value for R1 = 698kΩ.
(
)
–R2
ON
R1=R3 ×
Using standard 1% resistor values, the circuit’s nominal
1.223V
UV and OV thresholds are:
V
V
= 36.5V
= 71.2V
40V –1.223V
(
)
–R2
UV
OV
R1=12.4kΩ ×
1.223V
Programmable UVLO Hysteresis—MIC2594
R1= 391.380kΩ
The closest standard 1% value for R1 = 392kΩ.
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 significantly simplify dealing with source
impedancesinthesupplybuswhileatthesametimeincreasing
theamountofavailableoperatingtimefromalooselyregulated
power supply (for example, a battery supply). Similarly to the
MIC2588, each of these pins is internally connected to an
Using standard 1% resistor values, the circuit’s nominal
ON and OFF thresholds are:
V
V
= 40.1V
= 35V
ON
OFF
M9999-122303
12
December 2003
MIC2588/MIC2594
Micrel
thiswilldamagethetransistor.However,theactual
Applications Information
4-Wire Kelvin Sensing
avalanche voltage is unknown; all that can be
guaranteed is that it will be greater than the V
BD(D-
Because of the low value typically required for the sense
resistor,specialcaremustbeusedtomeasureaccuratelythe
voltage drop across it. Specifically, the measurement tech-
of the MOSFET. The drain of the transistor is
S)
connected to the DRAIN pin of the MIC2588/94,
and the resulting transient does have enough
voltage and energy and can damage this, or any,
high-voltage hot swap controller.
nique across each R
must employ 4-wire Kelvin sens-
SENSE
ing. This is simply a means of making sure that any voltage
drops in the power traces connecting to the resistors are not
picked up by the signal conductors measuring the voltages
across the sense resistors.
2. If the load’s bypass capacitance (for example, the
input filter capacitors for a set of DC-DC converter
modules) are on a board from which the board with
the MIC2589/MIC2595 and the MOSFET can be
unplugged, the same type of inductive transient
damage can occur to the MIC2588/MIC2594.
Figure 6 illustrates how to implement 4-wire Kelvin sensing.
Asthefigureshows,allthehighcurrentinthecircuit(fromV
EE
throughR
,andthentothesourceoftheoutputMOSFET)
SENSE
flowsdirectlythroughthepowerPCBtracesandR
voltage drop resulting across R
way that the high currents through the power traces will not
introduce any parasitic voltage drops in the sense leads. It is
recommended to connect the hot swap controller’s sense
leads directly to the sense resistor’s metalized contact pads.
.The
SENSE
Protecting the controller and the power MOSFET from dam-
age against these large-scale transients can take the forms
shown in Figure 7. It is not mandatory that these techniques
are used—the application environment will dictate suitability.
As protection against sudden on-card load dumps at the
DRAIN pin of the controller, a 2.2µF or larger capacitor
is sampled in such a
SENSE
RSENSE metalized
contact pads
directly from DRAIN to V of the controller can be used to
EE
serve as a charge reservoir. Alternatively, a 68V, 1W, 5%
Zener diode clamp can be installed in a similar fashion. Note
thattheclampdiode’scathodeisconnectedtotheDRAINpin
as shown in Figure 7. To protect the hot swap controller from
large-scale transients at the card input, a 100V clamp diode
(an SMAT70A or equivalent) can be used. In either case, the
lead lengths should be short and the layout compact to
prevent unwanted transients in the protection circuit.
Power Trace
From VEE
Power Trace
To MOSFET Source
RSENSE
PCB Track Width:
0.03" per Ampere
using 1oz Cu
Signal Trace
to MIC2588/94 VEE Pin
Signal Trace
to MIC2588/94 SENSE Pin
Note: Each SENSE lead trace shall be
balanced for best performance — equal
length/equal aspect ratio.
[Circuit drawing under construction]
Figure 6. 4-Wire Kelvin Sense Connections for R
Protection Against Voltage Transients
SENSE
Figure 7. Using Large-Scale Transient Protection
Devices Around the MIC2588/94
In many telecom applications, it is very common for circuit
boards to encounter large-scale supply-voltage transients in
backplane environments. Because backplanes present a
compleximpedanceenvironment, thesetransientscanbeas
high as 2.5 times steady-state levels, or 120V in worst-case
situations. In addition, a sudden load dump anywhere on the
circuitcardcangenerateaveryhighvoltagespikeatthedrain
of the output MOSFET which, in turn, will appear at the
DRAINpinoftheMIC2588/MIC2594. Inbothcases, itisgood
engineering practice to include protective measures to avoid
damaging sensitive ICs or the hot swap controller from these
large-scale transients. Two typical scenarios in which large-
scale transients occur are described below:
Power buss inductance could easily result in localized high-
voltage transients during a turn-off event. The potential for
overstressing the part in such a case should be kept in check
with a suitable input capacitor and/or transient clamping
diode.
Power MOSFET Selection
[Section under construction]
Power MOSFET Operating Voltage Requirements
[Section under construction]
Power MOSFET Steady-State Thermal Issues
1. Anoutputcurrentloaddumpwithnobypass(charge
bucket or bulk) capacitance to V . For example,
[Section under construction]
EE
if L
= 5µH, V = 56V and t
= 0.7µs, the
LOAD
IN
OFF
resulting peak short-circuit current prior to the
MOSFET turning off would reach:
Power MOSFET Transient Thermal Issues
[Section under construction]
55V × 0.7µs
(
)
= 7.7A
5µH
PCB Layout Considerations
Ifthereisnootherpathforthiscurrenttotakewhen
the MOSFET turns off, it will avalanche the drain-
source junction of the MOSFET. Since the total
energy represented is small relative to the sturdi-
ness of modern power MOSFETs, it’s unlikely that
[Section under construction]
Power MOSFET and Sense Resistor Vendors
[Section under construction]
December 2003
13
M9999-122303
MIC2588/MIC2594
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
45°
0.0098 (0.249)
0.0040 (0.102)
0.010 (0.25)
0.007 (0.18)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.064 (1.63)
0.045 (1.14)
0.244 (6.20)
0.228 (5.79)
8-Pin SOIC (M)
MICREL, INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2003 Micrel, Incorporated.
M9999-122303
14
December 2003
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