LTC4251B/LTC4251B-1/
LTC4251B-2
Negative Voltage
Hot Swap Controllers in SOT-23
FEATURES
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DESCRIPTION
The LTC
®
4251B/LTC4251B-1/LTC4251B-2 negative voltage
Hot Swap™ controllers allow a board to be safely inserted
and removed from a live backplane. Output current is con-
trolled by three stages of current limiting: a timed circuit
breaker, active current limiting and a fast feedforward path
that limits peak current under worst-case catastrophic
fault conditions.
Programmable undervoltage and overvoltage detectors
disconnect the load whenever the input supply exceeds
the desired operating range. The supply input is shunt
regulated, allowing safe operation with very high supply
voltages. A multifunction timer delays initial start-up and
controls the circuit breaker’s response time.
The LTC4251B UV/OV thresholds are designed to match
the standard telecom operating range of – 43V to –75V. The
LTC4251B-1 UV/OV thresholds extend the operating range
to encompass –36V to –72V. The LTC4251B-2 implements
a UV threshold of –43V only. The LTC4251B improves the
ruggedness of the LTC4251 shunt regulator.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Hot Swap and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Allows Safe Board Insertion and Removal from a
Live –48V Backplane
Floating Topology Permits Very High Voltage
Operation
Programmable Analog Current Limit with Circuit
Breaker Timer
Fast Response Time Limits Peak Fault Current
Improved Ruggedness Shunt Regulator
Programmable Timer
Programmable Undervoltage/Overvoltage Protection
Low Profile 6-Lead SOT-23 (ThinSOT™) Package
APPLICATIONS
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Hot Board Insertion
Electronic Circuit Breaker
–48V Distributed Power Systems
Negative Power Supply Control
Central Office Switching
Programmable Current Limiting Circuit
High Availability Servers
Disk Arrays
TYPICAL APPLICATION
–48V, 2.5A Hot Swap Controller
–48RTN
–48RTN
(SHORT PIN)
R1
402k
1%
C1
10nF
R2
32.4k
1%
R
IN
*
10k
500mW
D
IN†
DDZ13B**
V
IN
UV/OV
GATE
3
R
C
10Ω
C
C
18nF
4
*TWO 0.25W RESISTORS IN SERIES FOR
R
IN
ON THE PCB ARE RECOMMENDED.
**DIODES, INC.
†RECOMMENDED FOR HARSH ENVIRONMENTS
4251b12f
Start-Up Behavior
+
LOAD
V
OUT
Q1
IRF530S
SENSE
2.5A/DIV
C
L
100μF
C
IN
1μF
GATE
5V/DIV
LTC4251B
TIMER SENSE
V
EE
C
T
150nF
1
R
S
0.02Ω
2
4251b12 TA01a
V
OUT
20V/DIV
–48V
1ms/DIV
4251b12 TA01b
1
LTC4251B/LTC4251B-1/
LTC4251B-2
ABSOLUTE MAXIMUM RATINGS
(Note 1), All Voltages are Referred to V
EE
PIN CONFIGURATION
TOP VIEW
SENSE 1
V
EE
2
V
IN
3
6 GATE
5 UV/OV*
4 TIMER
Current into V
IN
(100μs Pulse) .............................100mA
Minimum V
IN
Voltage ............................................ – 0.3V
Gate, UV/OV, Timer Voltage........................ –0.3V to 16V
Sense Voltage ............................................ –0.6V to 16V
Current Out of Sense Pin (20μs Pulse).............. –200mA
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range
LTC4251BC/LTC4251BC-1/LTC4251BC-2....0°C to 70°C
LTC4251BI/LTC4251BI-1/LTC4251BI-2 .. –40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
S6 PACKAGE
6-LEAD PLASTIC SOT-23
*UV FOR LTC4251B-2
T
JMAX
= 125°C,
θ
JA
= 192°C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI)
LTC4251BCS6#TRMPBF
LTC4251BIS6#TRMPBF
LTC4251BIS6-1#TRMPBF
TAPE AND REEL
LTC4251BCS6#TRPBF
LTC4251BIS6#TRPBF
LTC4251BIS6-1#TRPBF
PART MARKING*
LTGCT
LTGCT
LTGDV
LTGDV
LTGDW
PACKAGE DESCRIPTION
6-Lead Plastic SOT-23
6-Lead Plastic SOT-23
6-Lead Plastic SOT-23
6-Lead Plastic SOT-23
6-Lead Plastic SOT-23
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
0°C to 70°C
–40°C to 85°C
LTC4251BCS6-1#TRMPBF LTC4251BCS6-1#TRPBF
LTC4251BCS6-2#TRMPBF LTC4251BCS6-2#TRPBF
LTC4251BIS6-2#TRMPBF LTC4251BIS6-2#TRPBF
LTGDW
6-Lead Plastic SOT-23
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on 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/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. (Notes 2, 3)
SYMBOL PARAMETER
V
Z
r
Z
I
IN
V
LKO
V
LKH
V
CB
V
ACL
V
FCL
I
GATE
V
IN
to V
EE
Zener Voltage
V
IN
to V
EE
Zener Dynamic Impedance
V
IN
Supply Current
V
IN
Undervoltage Lockout
V
IN
Undervoltage Lockout Hysteresis
Circuit Breaker Current Limit Voltage
Analog Current Limit Voltage
Fast Current Limit Voltage
GATE Pin Output Current
V
CB
= (V
SENSE
– V
EE
)
V
ACL
= (V
SENSE
– V
EE
)
V
FCL
= (V
SENSE
– V
EE
)
UV/OV = 4V, V
SENSE
= V
EE
, V
GATE
= 0V (Sourcing)
UV/OV = 4V, V
SENSE
– V
EE
= 0.15V, V
GATE
= 3V (Sinking)
UV/OV = 4V, V
SENSE
– V
EE
= 0.3V, V
GATE
= 1V (Sinking)
V
GATE
– V
EE
, I
IN
= 2mA
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ELECTRICAL CHARACTERISTICS
I
IN
= 2mA
CONDITIONS
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MIN
11.5
TYP
13
5
0.8
9.2
1
MAX
14.5
2
11.5
60
120
300
80
UNITS
V
Ω
mA
V
V
mV
mV
mV
μA
mA
mA
V
4251b12f
I
IN
= 2mA to 30mA
UV/OV = 4V, V
IN
= (V
Z
– 0.3V)
Coming Out of UVLO (Rising V
IN
)
40
80
150
40
50
100
200
58
17
190
12
V
GATE
External MOSFET Gate Drive
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V
Z
2
LTC4251B/LTC4251B-1/
LTC4251B-2
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
SYMBOL PARAMETER
V
GATEL
V
UVHI
V
UVLO
V
UVHST
V
OVHI
V
OVLO
V
OVHST
I
SENSE
I
INP
V
TMRH
V
TMRL
I
TMR
Gate Low Threshold
UV Threshold High
UV Threshold Low
UV Hysteresis
OV Threshold High
OV Threshold Low
OV Hysteresis
SENSE Input Current
UV/OV Input Current
Timer Voltage High Threshold
Timer Voltage Low Threshold
Timer Current
Timer On (Initial Cycle, Sourcing), V
TMR
= 2V
Timer Off (Initial Cycle, Sinking), V
TMR
= 2V
Timer On (Circuit Breaker, Sourcing), V
TMR
= 2V
Timer Off (Cooling Cycle, Sinking), V
TMR
= 2V
LTC4251B/LTC4251B-1
CONDITIONS
(Before Gate Ramp-Up)
LTC4251B/LTC4251B-2
LTC4251B-1
LTC4251B/LTC4251B-2
LTC4251B-1
LTC4251B/LTC4251B-2
LTC4251B-1
LTC4251B
LTC4251B-1
LTC4251B
LTC4251B-1
LTC4251B
LTC4251B-1
UV/OV = 4V, V
SENSE
= 50mV
UV/OV = 4V
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ELECTRICAL CHARACTERISTICS
MIN
3.075
2.300
2.775
2.050
TYP
0.5
3.225
2.420
2.925
2.160
0.30
0.26
MAX
3.375
2.540
3.075
2.270
UNITS
V
V
V
V
V
V
V
5.85
5.86
5.25
5.61
6.15
6.17
5.55
5.91
0.60
0.26
6.45
6.48
5.85
6.21
V
V
V
V
V
V
μA
–30
–15
±0.1
4
1
5.8
28
230
5.8
0.7
1
±1
μA
V
V
μA
mA
μA
μA
μs
μs
t
PLLUG
t
PHLOG
UV Low to GATE Low
OV High to GATE Low
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.
Note 3:
UV/OV = 4V refers to UV = 4V for the LTC4251B-2.
TYPICAL PERFORMANCE CHARACTERISTICS
I
IN
vs Temperature
2000
1800
1600
1400
I
IN
(mA)
I
IN
(μA)
1200
1000
800
600
400
200
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G01
UV/OV = 4V refers to UV = 4V for the LTC4251B-2.
r
Z
vs Temperature
I
IN
= 2mA
V
IN
= (V
Z
– 0.3V)
1000
I
IN
vs V
IN
T
A
= –40°C
10
9
8
T
A
= 25°C
r
Z
(Ω)
7
6
5
100
10
T
A
= 85°C
T
A
= 125°C
1
4
3
0.1
0
2
4
6
8 10 12 14 16 18 20 22
V
IN
(V)
4251b12 G02
2
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G03
4251b12f
3
LTC4251B/LTC4251B-1/
LTC4251B-2
TYPICAL PERFORMANCE CHARACTERISTICS
V
Z
vs Temperature
14.5
I
IN
= 2mA
12.0
11.5
14.0
11.0
10.5
V
LKO
(V)
10.0
9.5
9.0
8.5
12.0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G04
UV/OV = 4V refers to UV = 4V for the LTC4251B-2.
Undervoltage Lockout Hysteresis
V
LKH
vs Temperature
1.6
1.4
1.2
1
V
LKH
0.8
0.6
0.4
0.2
Undervoltage Lockout V
LKO
vs
Temperature
13.5
V
Z
(V)
13.0
12.5
8.0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G05
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G06
Circuit Breaker Current Limit
Voltage V
CB
vs Temperature
60
58
56
54
V
CB
(mV)
V
ACL
(V)
52
50
48
46
44
42
40
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G07
Analog Current Limit Voltage V
ACL
vs Temperature
120
115
110
V
FCL
(mV)
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G08
Fast Current Limit Voltage V
FCL
vs Temperature
300
275
250
225
200
175
150
–55 –35 –15
105
100
95
90
85
80
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G09
I
GATE
(Source) vs Temperature
70
UV/0V = 4V
TIMER = 0V
65 V
SENSE
= V
EE
V
GATE
= 0V
60
I
GATE
(mA)
I
GATE
(μA)
55
50
45
40
–55 –35 –15
30
25
20
I
GATE
(ACL, Sink) vs Temperature
UV/0V = 4V
TIMER = 0V
V
SENSE
– V
EE
= 0.15V
V
GATE
= 3V
I
GATE
(mA)
400
350
300
250
200
150
100
5
0
–55 –35 –15
50
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G11
I
GATE
(FCL, Sink) vs Temperature
UV/0V = 4V
TIMER = 0V
V
SENSE
– V
EE
= 0.3V
V
GATE
= 1V
15
10
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G10
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G12
4251b12f
4
LTC4251B/LTC4251B-1/
LTC4251B-2
TYPICAL PERFORMANCE CHARACTERISTICS
V
GATE
vs Temperature
14.5
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G13
UV/OV = 4V refers to UV = 4V for the LTC4251B-2.
V
GATEL
vs Temperature
0.8
0.7
0.6
V
GATEL
(V)
0.5
0.4
0.3
0.2
0.1
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G14
UV Threshold vs Temperature
3.375
LTC4251B/LTC4251B-2
3.275
UV THRESHOLD (V)
3.175
3.075
2.975
2.875
2.775
–55 –35 –15
V
UVH
UV/0V = 4V
V
TMR
= 0V
V
SENSE
= V
EE
UV/0V = 4V,
V
TMR
= 0V,
GATE THRESHOLD
BEFORE RAMP-UP
V
GATE
(V)
V
UVL
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G15
UV Threshold vs Temperature
2.55
2.50
2.45
UV THRESHOLD (V)
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G16
OV Threshold vs Temperature
6.45
6.51
LTC4251B
6.25
6.41
V
OVH
OV THRESHOLD (V)
6.31
6.21
6.11
6.01
5.91
5.81
5.45
5.71
5.25
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G17
OV Threshold vs Temperature
LTC4251B-1
LTC4251B-1
V
UVHI
OV THRESHOLD (V)
6.05
5.85
5.65
V
OVHI
V
UVLO
V
OVL
V
OVLO
5.61
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G18
I
SENSE
vs Temperature
–10
–12
–14
–16
–I
SENSE
(mA)
I
SENSE
(μA)
–18
–20
–22
–24
–26
–28
–30
–55 –35 –15
UV/0V = 4V
TIMER = 0V
GATE = HIGH
V
SENSE
– V
EE
= 50mV
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G19
I
SENSE
vs (V
SENSE
– V
EE
)
0.01
5.0
4.5
0.1
TIMER THRESHOLD (V)
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
TIMER Threshold vs Temperature
V
TMRH
1.0
10
UV/0V = 4V
TIMER = 0V
GATE = HIGH
T
A
= 25°C
1.5
2.0
100
V
TMRL
1000
–1.5 –1.0 –0.5
0
0.5 1.0
(V
SENSE
– V
EE
) (V)
0
–55 –35 –15
5 25 45 65 85 105 125
TEMPERATURE (°C)
4251b12 G21
4251b12 G20
4251b12f
5
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