LTC4251/LTC4251-1/
LTC4251-2
1
425112f
s
Hot Board Insertion
s
Electronic Circuit Breaker
s
48V Distributed Power Systems
s
Negative Power Supply Control
s
Central Office Switching
s
Programmable Current Limiting Circuit
s
High Availability Servers
s
Disk Arrays
s
Allows Safe Board Insertion and Removal from a
Live 48V Backplane
s
Floating Topology Permits Very High Voltage
Operation
s
Low Profile (1mm) ThinSOT
TM
Package
s
Programmable Analog Current Limit with Circuit
Breaker Timer
s
Fast Response Time Limits Peak Fault Current
s
Programmable Timer
s
Programmable Undervoltage/Overvoltage Protection
Negative Voltage
Hot Swap Controllers in SOT-23
48V, 2.5A Hot Swap Controller
The LTC
4251/LTC4251-1/LTC4251-2 negative voltage
Hot Swap
TM
controllers allow a board to be safely inserted
and removed from a live backplane. Output current is
controlled 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 LTC4251 UV/OV thresholds are designed to match the
standard telecom operating range of 43V to 75V. The
LTC4251-1 UV/OV thresholds extend the operating range
to encompass 36V to 72V. The LTC4251-2 implements
a UV threshold of 43V only.
All parts are available in the 6-Pin SOT-23 package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT and Hot Swap are trademarks of Linear Technology Corportation.
Start-Up Behavior
GATE
5V/DIV
SENSE
2.5A/DIV
V
OUT
20V/DIV
425112 TA02
1ms/DIV
+
LTC4251
UV/OV
TIMER
GATE
SENSE
V
IN
V
EE
1
2
3
4
5
6
LOAD
GND
GND
(SHORT PIN)
R1
402k
1%
R
C
10
R
S
0.02
R2
32.4k
1%
48V
C
T
150nF
C1
10nF
C
C
18nF
C
IN
1
F
C
L
100
F
R
IN
*
10k
500mW
V
OUT
Q1
IRF530S
425112 TA01
4
3
2
1
*TWO 0.25W RESISTORS IN SERIES FOR
R
IN
ON THE PCB ARE RECOMMENDED.
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
LTC4251/LTC4251-1/
LTC4251-2
2
425112f
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Z
V
IN
to V
EE
Zener Voltage
I
IN
= 2mA
q
12
13
14.5
V
r
Z
V
IN
to V
EE
Zener Dynamic Impedance
I
IN
= 2mA to 30mA
5
I
IN
V
IN
Supply Current
UV/OV = 4V, V
IN
= (V
Z
0.3V)
q
0.8
2
mA
V
LKO
V
IN
Undervoltage Lockout
Coming out of UVLO (Rising V
IN
)
q
9.2
12
V
V
LKH
V
IN
Undervoltage Lockout Hysteresis
1
V
V
CB
Circuit Breaker Current Limit Voltage
V
CB
= (V
SENSE
V
EE
)
q
40
50
60
mV
V
ACL
Analog Current Limit Voltage
V
ACL
= (V
SENSE
V
EE
)
q
80
100
120
mV
V
FCL
Fast Current Limit Voltage
V
FCL
= (V
SENSE
V
EE
)
q
150
200
300
mV
I
GATE
GATE Pin Output Current
UV/OV = 4V, V
SENSE
= V
EE
, V
GATE
= 0V (Sourcing)
q
40
58
80
A
UV/OV = 4V, V
SENSE
V
EE
= 0.15V, V
GATE
= 3V (Sinking)
17
mA
UV/OV = 4V, V
SENSE
V
EE
= 0.3V, V
GATE
= 1V (Sinking)
190
mA
V
GATE
External MOSFET Gate Drive
V
GATE
V
EE
, I
IN
= 2mA
q
10
12
V
Z
V
V
GATEL
Gate Low Threshold
(Before Gate Ramp-Up)
0.5
V
V
UVHI
UV Threshold High
LTC4251/LTC4251-2
q
3.075
3.225
3.375
V
LTC4251-1
q
2.300
2.420
2.540
V
V
UVLO
UV Threshold Low
LTC4251/LTC4251-2
q
2.775
2.925
3.075
V
LTC4251-1
q
2.050
2.160
2.270
V
V
UVHST
UV Hysteresis
LTC4251/LTC4251-2
0.30
V
LTC4251-1
0.26
V
V
OVHI
OV Threshold High
LTC4251
q
5.85
6.15
6.45
V
LTC4251-1
q
5.86
6.17
6.48
V
ABSOLUTE AXI U
RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
Current into V
IN
(100
s 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 (20
s Pulse) ............. 200mA
Maximum Junction Temperature .......................... 125
C
Operating Temperature Range
LTC4251C/LTC4251-1C/LTC4251-2C ...... 0
C to 70
C
LTC4251I/LTC4251-1I/LTC4251-2I .... 40
C to 85
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
ORDER PART NUMBER
S6 PART MARKING
T
JMAX
= 125
C,
JA
= 256
C/W
LTC4251CS6
LTC4251IS6
LTC4251-1CS6
LTC4251-1IS6
LTC4251-2CS6
LTC4251-2IS6
(Note 1), All Voltages are Referred to V
EE
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. (Notes 2, 3)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTUQ
LTUR
LTQU
LTQV
LTK6
LTAAZ
SENSE 1
V
EE
2
V
IN
3
6 GATE
5 UV/OV*
4 TIMER
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC SOT-23
*UV FOR LTC4251-2
LTC4251/LTC4251-1/
LTC4251-2
3
425112f
TEMPERATURE (
C)
55
I
IN
(
A)
2000
1800
1600
1400
1200
1000
800
600
400
200
0
15
25
45
125
425112 G01
35
5
65
85 105
V
IN
= (V
Z
0.3V)
V
IN
(V)
0
2
4
6
8
10 12 14 16 18 20 22
I
IN
(mA)
1000
100
10
1
0.1
425112 G02
T
A
= 40
C
T
A
= 125
C
T
A
= 25
C
T
A
= 85
C
TEMPERATURE (
C)
55
r
Z
(
)
10
9
8
7
6
5
4
3
2
15
25
45
125
425112 G03
35
5
65
85 105
I
IN
= 2mA
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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.
I
IN
vs Temperature
I
IN
vs V
IN
r
Z
vs Temperature
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. (Notes 2, 3)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
OVLO
OV Threshold Low
LTC4251
q
5.25
5.55
5.85
V
LTC4251-1
q
5.61
5.91
6.21
V
V
OVHST
OV Hysteresis
LTC4251
0.60
V
LTC4251-1
0.26
V
I
SENSE
SENSE Input Current
UV/OV = 4V, V
SENSE
= 50mV
q
30
15
A
I
INP
UV/OV Input Current
UV/OV = 4V
q
0.1
1
A
V
TMRH
Timer Voltage High Threshold
4
V
V
TMRL
Timer Voltage Low Threshold
1
V
I
TMR
Timer Current
Timer On (Initial Cycle, Sourcing), V
TMR
= 2V
5.8
A
Timer Off (Initial Cycle, Sinking), V
TMR
= 2V
28
mA
Timer On (Circuit Breaker, Sourcing), V
TMR
= 2V
230
A
Timer Off (Cooling Cycle, Sinking), V
TMR
= 2V
5.8
A
t
PLLUG
UV Low to GATE Low
0.7
s
t
PHLOG
OV High to GATE Low
LTC4251/LTC4251-1
1
s
Note 3: UV/OV = 4V refers to UV = 4V for the LTC4251-2.
UV/OV = 4V refers to UV = 4V for the LTC4251-2.
LTC4251/LTC4251-1/
LTC4251-2
4
425112f
Circuit Breaker Current Limit
Voltage V
CB
vs Temperature
Analog Current Limit Voltage V
ACL
vs Temperature
Fast Current Limit Voltage V
FCL
vs Temperature
I
GATE
(Source) vs Temperature
I
GATE
(ACL, Sink) vs Temperature
I
GATE
(FCL, Sink) vs Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
TEMPERATURE (
C)
55
V
CB
(mV)
60
58
56
54
52
50
48
46
44
42
40
15
25
45
125
425112 G07
35
5
65
85 105
TEMPERATURE (
C)
55
V
ACL
(V)
120
115
110
105
100
95
90
85
80
15
25
45
125
425112 G08
35
5
65
85 105
TEMPERATURE (
C)
55
V
FCL
(mV)
300
275
250
225
200
175
150
15
25
45
125
425112 G09
35
5
65
85 105
TEMPERATURE (
C)
55
I
GATE
(
A)
70
65
60
55
50
45
40
15
25
45
125
425112 G10
35
5
65
85 105
UV/0V = 4V
TIMER = 0V
V
SENSE
= V
EE
V
GATE
= 0V
TEMPERATURE (
C)
55
I
GATE
(mA)
30
25
20
15
10
5
0
15
25
45
125
425112 G11
35
5
65
85 105
UV/0V = 4V
TIMER = 0V
V
SENSE
V
EE
= 0.15V
V
GATE
= 3V
TEMPERATURE (
C)
55
I
GATE
(mA)
400
350
300
250
200
150
100
50
0
15
25
45
125
425112 G12
35
5
65
85 105
UV/0V = 4V
TIMER = 0V
V
SENSE
V
EE
= 0.3V
V
GATE
= 1V
UV/OV = 4V refers to UV = 4V for the LTC4251-2.
TEMPERATURE (
C)
55
V
Z
(V)
14.5
14.0
13.5
13.0
12.5
12.0
15
25
45
125
425112 G04
35
5
65
85 105
I
IN
= 2mA
TEMPERATURE (
C)
55
V
LKO
(V)
12.0
11.5
11.0
10.5
10.0
9.5
9.0
8.5
8.0
15
25
45
125
425112 G05
35
5
65
85 105
TEMPERATURE (
C)
55
V
LKH
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
15
25
45
125
425112 G06
35
5
65
85 105
V
Z
vs Temperature
Undervoltage Lockout V
LKO
vs
Temperature
Undervoltage Lockout Hysteresis
V
LKH
vs Temperature
LTC4251/LTC4251-1/
LTC4251-2
5
425112f
OV Threshold vs Temperature
I
SENSE
vs Temperature
I
SENSE
vs (V
SENSE
V
EE
)
TIMER Threshold vs Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
V
GATE
vs Temperature
V
GATEL
vs Temperature
UV Threshold vs Temperature
TEMPERATURE (
C)
55
V
GATE
(V)
14.5
14.0
13.5
13.0
12.5
12.0
11.5
11.0
10.5
10.0
15
25
45
125
425112 G13
35
5
65
85 105
UV/0V = 4V
V
TMR
= 0V
V
SENSE
= V
EE
TEMPERATURE (
C)
55
V
GATEL
(V)
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
15
25
45
125
425112 G14
35
5
65
85 105
UV/0V = 4V,
V
TMR
= 0V,
GATE THRESHOLD
BEFORE RAMP-UP
TEMPERATURE (
C)
55
UV THRESHOLD (V)
3.375
3.275
3.175
3.075
2.975
2.875
2.775
15
25
45
125
425112 G15
35
5
65
85 105
V
UVH
LTC4251/LTC4251-2
V
UVL
TEMPERATURE (
C)
55
OV THRESHOLD (V)
6.45
6.25
6.05
5.85
5.65
5.45
5.25
15
25
45
125
425112 G17
35
5
65
85 105
V
OVH
LTC4251
V
OVL
TEMPERATURE (
C)
55
I
SENSE
(
A)
10
12
14
16
18
20
22
24
26
28
30
15
25
45
125
425112 G19
35
5
65
85 105
UV/0V = 4V
TIMER = 0V
GATE = HIGH
V
SENSE
V
EE
= 50mV
(V
SENSE
V
EE
) (V)
1.5
1.0 0.5
0
0.5
1.0
1.5
2.0
I
SENSE
(mA)
0.01
0.1
1.0
10
100
1000
425112 G20
UV/0V = 4V
TIMER = 0V
GATE = HIGH
T
A
= 25
C
TEMPERATURE (
C)
55
TIMER THRESHOLD (V)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
15
25
45
125
425112 G21
35
5
65
85 105
V
TMRH
V
TMRL
TEMPERATURE (
C)
55
UV THRESHOLD (V)
2.55
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
15
25
45
125
425112 G16
35
5
65
85 105
V
UVHI
LTC4251-1
V
UVLO
TEMPERATURE (
C)
55
OV THRESHOLD (V)
6.51
6.41
6.31
6.21
6.11
6.01
5.91
5.81
5.71
5.61
15
25
45
125
425112 G18
35
5
65
85 105
V
OVHI
V
OVLO
LTC4251-1
UV Threshold vs Temperature
OV Threshold vs Temperature
UV/OV = 4V refers to UV = 4V for the LTC4251-2.
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