controllers that allow a board to be safely inserted and
removed from a live backplane. Inrush current is limited
to a programmable value by controlling the gate voltage
of an external N-channel pass transistor. The pass tran-
sistor is turned off if the input voltage is less than the
programmable undervoltage threshold or greater than
the overvoltage threshold. A programmable current limit
protects the system against shorts. After a 500μs timeout
the current limit activates the electronic circuit breaker.
The
PWRGD
(LT4250L) or PWRGD (LT4250H) signal can
be used to directly enable a power module. The LT4250L
is designed for modules with a low enable input and the
LT4250H for modules with a high enable input.
The LT4250L/LT4250H are available in 8-pin PDIP and
SO packages
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Hot Swap is a
trademark of Linear Technology Corporation.
Allows Safe Board Insertion and Removal from a
Live –48V Backplane
Circuit Breaker Immunity to Voltage Steps and
Current Spikes
Programmable Inrush and Short-Circuit Current
Limits
Pin Compatible With LT1640L/LT1640H
Operates from –18V to –80V
Programmable Overvoltage Protection
Programmable Undervoltage Lockout
Power Good Control Output
Bell-Core Compatible
ON/OFF
Threshold
APPLICATIONS
n
n
n
Central Office Switching
–48V Distributed Power Systems
Negative Power Supply Control
TYPICAL APPLICATION
Voltage Step on Input Supply
–48V RTN
(SHORT PIN)
–48V RTN
R4
†
549k
1%
3
R5
†
6.49k
1%
R6
†
10k
1%
UV
LT4250L
2
OV
V
EE
4
SENSE
5
GATE
6
R3
†
1k, 5%
0.1μF
10V
C1
†
470nF
25V
R2
10Ω
5%
C2
†
15nF
100V
2
ON/OFF
9
V
OUT+
8
SENSE
+
7
TRIM
6
SENSE
–
4
5
V
OUT–
V
IN–
1
C4
100μF
100V
V
IN+
LUCENT
JW050A1-E
5V
500μs/DIV
4250 TA01b
8
V
DD
1
V
EE
AND
DRAIN
20V/DIV
UV =
38.5V
UV
RELEASE
AT 43V
OV =
71V
PWRGD
DRAIN
7
I
D
(Q1)
5A/DIV
*
–48V
INPUT 1
R1
0.02Ω
5%
†
Q1
IRF530
–48V
INPUT 2
* DIODES INC. SMAT70A
†
THESE COMPONENTS ARE APPLICATION
SPECIFIC AND MUST BE SELECTED BASED
UPON OPERATING CONDITIONS AND DESIRED
PERFORMANCE. SEE APPLICATIONS
INFORMATION.
C3
0.1μF
100V
+
+
C5
100μF
16V
4250 TA01a
4250lhfa
1
LT4250L/LT4250H
ABSOLUTE MAXIMUM RATINGS
(Note 1), All Voltages Referred to V
EE
Supply Voltage (V
DD
– V
EE
) ...................... –0.3V to 100V
PWRGD,
PWRGD Pins ............................. –0.3V to 100V
SENSE, GATE Pins ..................................... –0.3V to 20V
UV, OV Pins ................................................ –0.3V to 60V
DRAIN Pin ................................................... –2V to 100V
Maximum Junction Temperature........................... 125°C
Operating Temperature Range
LT4250LC/LT4250HC ............................... 0°C to 70°C
LT4250LI/LT4250HI.............................. –40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
PIN CONFIGURATION
TOP VIEW
PWRGD
1
OV 2
UV 3
V
EE
4
8
7
6
5
V
DD
DRAIN
GATE
SENSE
PWRGD 1
OV 2
UV 3
V
EE
4
N8 PACKAGE
8-LEAD PDIP
TOP VIEW
8
7
6
5
V
DD
DRAIN
GATE
SENSE
N8 PACKAGE
S8 PACKAGE
8-LEAD PDIP
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 120°C/W (N8)
T
JMAX
= 125°C,
θ
JA
= 150°C/W (S8)
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 120°C/W (N8)
T
JMAX
= 125°C,
θ
JA
= 150°C/W (S8)
ORDER INFORMATION
LEAD FREE FINISH
LT4250LCN8#PBF
LT4250LCS8#PBF
LT4250LIN8#PBF
LT4250LIS8#PBF
LT4250HCN8#PBF
LT4250HCS8#PBF
LT4250HIN8#PBF
LT4250HIS8#PBF
TAPE AND REEL
LT4250LCN8#TRPBF
LT4250LCS8#TRPBF
LT4250LIN8#TRPBF
LT4250LIS8#TRPBF
LT4250HCN8#TRPBF
LT4250HCS8#TRPBF
LT4250HIN8#TRPBF
LT4250HIS8#TRPBF
PART MARKING
4250L
4250L
4250LI
4250LI
4250H
4250H
4250HI
4250HI
PACKAGE DESCRIPTION
8-Lead PDIP
8-Lead PLASTIC SO
8-Lead PDIP
8-Lead PLASTIC SO
8-Lead PDIP
8-Lead PLASTIC SO
8-Lead PDIP
8-Lead PLASTIC SO
TEMPERATURE RANGE
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
0°C to 70°C
0°C to 70°C
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
4250lhfa
2
LT4250L/LT4250H
ELECTRICAL CHARACTERISTICS
SYMBOL
DC
V
DD
I
DD
V
UVL
V
CL
I
PU
I
PD
I
SENSE
ΔV
GATE
V
UVH
V
UVL
V
UVHY
I
INUV
V
OVH
V
OVL
V
OVHY
I
INOV
V
DL
V
GH
I
DRAIN
V
OL
Supply Voltage Operating Range
Supply Current
Undervoltage Lockout
Current Limit Trip Voltage
GATE Pin Pull-Up Current
GATE Pin Pull-Down Current
SENSE Pin Current
External Gate Drive
UV Pin High Threshold Voltage
UV Pin Low Threshold Voltage
UV Pin Hysteresis
UV Pin Input Current
OV Pin High Threshold Voltage
OV Pin Low Threshold Voltage
OV Pin Hysteresis
OV Pin Input Current
DRAIN Low Threshold
GATE High Threshold
Drain Input Bias Current
PWRGD
Output Low Voltage
V
OV
= V
EE
V
DRAIN
– V
EE
, DRAIN Decreasing
ΔV
GATE
– V
GATE
Decreasing
V
DRAIN
= 48V
PWRGD
(LT4250L), (V
DRAIN
– V
EE
) < V
DL
I
OUT
= 1mA
I
OUT
= 5mA
PWRGD (LT4250H), V
DRAIN
= 5V
I
OUT
= 1mA
PWRGD
(LT4250L), V
DRAIN
= 48V, V
PWRGD
= 80V
PWRGD (LT4250H), V
DRAIN
= 0V, V
PWRGD
= 80V
Figures 1a, 2
Figures 1a, 3
Figures 1a, 2
Figures 1a, 3
Figures 1a, 4a
Figures 1b, 4b
l
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Note 2), V
DD
= 48V, V
EE
= 0V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
18
1.6
15.4
V
CL
= (V
SENSE
– V
EE
)
Gate Drive On, V
GATE
= V
EE
Gate Drive OFF
V
SENSE
= 50mV
(V
GATE
– V
EE
), 18V ≤ V
DD
≤ 80V
UV Increasing
UV Decreasing
V
UV
= V
EE
OV Increasing
OV Decreasing
l
l
l
l
l
TYP
MAX
80
5
60
–60
70
18
1.27
1.145
–0.5
1.275
1.255
–0.5
2.3
500
0.8
3
1
10
10
UNITS
V
mA
V
mV
μA
mA
μA
V
V
V
mV
μA
V
V
mV
μA
V
V
μA
V
V
V
μA
μA
μs
μs
μs
μs
UV = 3V, OV = V
EE
, SENSE = V
EE
l
40
–30
24
10
1.24
1.105
50
–45
50
–20
13.5
1.255
1.125
130
–0.02
l
l
l
1.235
1.21
1.255
1.235
20
–0.03
1.1
10
1.6
1.3
80
0.48
1.2
0.75
0.05
0.05
1.7
1.5
5.5
6.5
1
500
1
1
1.5
1.5
PWRGD Output Low Voltage
(PWRGD – DRAIN)
I
OH
AC
t
PHLOV
t
PHLUV
t
PLHOV
t
PLHUV
t
PHLSENSE
t
PHLCB
t
PHLDL
t
PHLGH
OV High to GATE Low
UV Low to GATE Low
OV Low to GATE High
UV High to GATE High
SENSE High to Gate Low
Current Limit to GATE Low
Output Leakage
3
μs
μs
μs
μs
μs
μs
DRAIN Low to
PWRGD
Low
(LT4250L) Figures 1a, 5a
DRAIN Low to (PWRGD – DRAIN) High (LT4250H) Figures 1a, 5a
GATE High to
PWRGD
Low
(LT4250L) Figures 1a, 5b
GATE High to (PWRGD – DRAIN) High (LT4250H) Figures 1a, 5b
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to V
EE
unless otherwise
specified.
4250lhfa
3
LT4250L/LT4250H
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Supply Voltage
1.8
1.7
SUPPLY CURRENT (mA)
1.6
1.5
1.4
1.3
1.2
1.1
0
0
20
80
60
SUPPLY VOLTAGE (V)
40
100
4250 G01
Supply Current vs Temperature
1.6
15
V
DD
= 48V
1.5
SUPPLY CURRENT (mA)
GATE VOLTAGE (V)
1.4
1.3
1.2
1.1
7
1.0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4250 G02
Gate Voltage vs Supply Voltage
T
A
= 25°C
14
13
12
11
10
9
8
T
A
= 25°C
6
0
20
80
60
40
SUPPLY VOLTAGE (V)
100
4250 G03
Gate Voltage vs Temperature
15.0
V
DD
= 48V
14.5
14.0
13.5
13.0
12.5
12.0
–50
TRIP VOLTAGE (mV)
GATE VOLTAGE (V)
55
54
Current Limit Trip Voltage
vs Temperature
48
47
GATE PULL-UP CURRENT (μA)
46
45
44
43
42
41
–25
50
0
25
TEMPERATURE (°C)
75
100
4250 G05
Gate Pull-Up Current
vs Temperature
V
GATE
= 0V
53
52
51
50
49
48
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
4250 G04
40
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4250 G06
Gate Pull-Down Current
vs Temperature
55
PWRGD
OUTPUT LOW VOLTAGE (V)
GATE PULL-DOWN CURRENT (mA)
V
GATE
= 2V
52
0.5
PWRGD
Output Low Voltage
vs Temperature (LT4250L)
8
I
OUT
= 1mA
OUTPUT IMPEDANCE (kΩ)
0.4
7
6
5
4
3
PWRGD Output Impedance
vs Temperature (LT4250H)
V
DRAIN
– V
EE
> 2.4V
49
0.3
46
0.2
43
0.1
40
–50
–25
0
50
25
TEMPERATURE (°C)
75
100
4250 G07
0
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
4250 G08
2
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4250 G09
4250lhfa
4
LT4250L/LT4250H
PIN FUNCTIONS
PWRGD/PWRGD
(Pin 1):
Power Good Output Pin. This pin
will latch a power good indication when V
DRAIN
is within
V
DL
of V
EE
and V
GATE
is within V
GH
of
ΔV
GATE
. This pin
can be connected directly to the enable pin of a power
module.
When the DRAIN pin of the LT4250L is above V
EE
by more
than V
DL
or V
GATE
is more than V
GH
from
ΔV
GATE
, the
PWRGD
pin will be high impedance, allowing the pull-up
current of the module’s enable pin to pull the pin high and
turn the module off. When V
DRAIN
drops below V
DL
and
V
GATE
rises above V
GH
, the
PWRGD
pin sinks current to
V
EE
, pulling the enable pin low and turning on the module.
This condition is latched until the GATE pin is turned off
via the UV, OV, UVLO or the electronic circuit breaker.
When the DRAIN pin of the LT4250H is above V
EE
by more
than V
DL
or V
GATE
is more than V
GH
from
ΔV
GATE
, the
PWRGD pin will sink current to the DRAIN pin which pulls
the module’s enable pin low, forcing it off. When V
DRAIN
drops below V
DL
and V
GATE
rises above V
GH
, the PWRGD
sink current is turned off, allowing the module’s pull-up
current to pull the enable pin high and turn on the module.
This condition is latched until the GATE pin is turned off
via the UV, OV, UVLO or the electronic circuit breaker.
OV (Pin 2):
Analog Overvoltage Input. When OV is pulled
above the 1.255V threshold, an overvoltage condition is
detected and the GATE pin will be immediately pulled low.
The GATE pin will remain low until OV drops below the
1.235V threshold.
UV (Pin 3):
Analog Undervoltage Input. When UV is pulled
below the 1.125V threshold, an undervoltage condition
is detected and the GATE pin will be immediately pulled
low. The GATE pin will remain low until UV rises above
the 1.255 threshold.
The UV pin is also used to reset the electronic circuit
breaker. If the UV pin is cycled low and high following the
trip of the circuit breaker, the circuit breaker is reset and a
normal power-up sequence will occur. The response time
for this pin is 1.5μs. Add an external capacitor to this pin
for additional filtering.
V
EE
(Pin 4):
Negative Supply Voltage Input. Connect to
the lower potential of the power supply.
SENSE (Pin 5):
Circuit Breaker Sense Pin. With a sense
resistor placed in the supply path between V
EE
and SENSE,
the overcurrent condition will pull down the GATE pin and
regulate the voltage across the resistor to be 50mV. If
the overcurrent condition exists for more than 500μs the
electronic circuit breaker will trip and turnoff the external
MOSFET.
If the current limit value is set to twice the normal operating
current, only 25mV is dropped across the sense resistor
during normal operation. To disable the current limit feature,
V
EE
and SENSE can be shorted together.
GATE (Pin 6):
Gate Drive Output for the External N-channel
MOSFET. The GATE pin will go high when the following
start-up conditions are met: the UV pin is high, the OV pin
is low, (V
SENSE
– V
EE
) < 50mV and the V
DD
pin is greater
than V
UVLOH
. The GATE pin is pulled high by a 45μA cur-
rent source and pulled low with a 50mA current source.
During current limit the GATE pin is pulled low using a
100mA current source.
DRAIN (Pin 7):
Analog Drain Sense Input. Connect this
pin to the drain of the external N-channel MOSFET and
the V
–
pin of the power module. When the DRAIN pin is
below V
DL
, the
PWRGD/PWRGD
pin will latch to indicate
the switch is on.
V
DD
(Pin 8):
Positive Supply Voltage Input. Connect this
pin to the higher potential of the power supply inputs and
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