LT4254
Positive High Voltage
Hot Swap Controller
with Open-Circuit Detect
FEATURES
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DESCRIPTIO
Allows Safe Board Insertion and Removal from a
Live Backplane
Controls Supply Voltage from 10.8V to 36V
Foldback Current Limiting
Open Circuit and Overcurrent Fault Detect
Drives an External N-Channel MOSFET
Automatic Retry or Latched Off Operation
After Overcurrent Fault
Programmable Supply Voltage Power-Up Rate
Undervoltage and Overvoltage Protection
Open MOSFET Detection
Available in 16-Lead SSOP Package
The LT
®
4254 is a high voltage Hot Swap controller that
allows a board to be safely inserted and removed from a
live backplane. An internal driver controls the high side
N-channel MOSFET gate for supply voltages ranging from
10.8V to 36V. The part features an open-circuit detect
(OPEN) output that indicates abnormally low load current
conditions.
The LT4254 features an adjustable analog foldback cur-
rent limit. If the supply remains in current limit for more
than a programmable time, the N-channel MOSFET shuts
off, the PWRGD output goes low and the LT4254 either
automatically restarts after a time-out delay or latches off
until the UV pin is cycled low. The RETRY pin sets whether
the part will automatically restart after an overcurrent fault
or if it will latch off until the UV pin is cycled low.
The PWRGD output indicates when the output voltage
rises above a programmed level. An external resistor
string from V
CC
provides programmable undervoltage and
overvoltage protection.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Hot Board Insertion
Electronic Circuit Breaker/Power Bussing
Industrial High Side Switch/Circuit Breaker
24V Industrial/Alarm Systems
12V and 24V Distributed Power Systems
TYPICAL APPLICATIO
V
IN
24V
(SHORT PIN)
R1
324k
UV
C3
0.1µF
LT4254
V
CC
SENSE
R5
0.025Ω
24V, 2A Hot Swap Controller
Q1
IRF530
D1
CMPZ5241B
11V
R6
10Ω
R7
100Ω
C1
10nF
FB
RETRY
PWRGD
GND
UV = 20V
OV = 40V
PWRGD = 18V
R9
40.2k
PWRGD
4254 TA01
C
L
R8
140k
R4
27k
V
OUT
24V
1.5A
GATE
V
IN
20V/DIV
V
OUT
20V/DIV
INRUSH
CURRENT
500mA/DIV
PWRGD
20V/DIV
R2
40.2k
OV
R3
40.2k
C2
33nF
OPEN
TIMER
GND
U
TM
U
U
LT4254 Start-Up Behavior
CONTACT BOUNCE
C
L
= 168µF
2.5ms/DIV
4245 TA02
4254fb
1
LT4254
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
UV
OV
NC
OPEN
PWRGD
NC
RETRY
GND
1
2
3
4
5
6
7
8
16 V
CC
15 SENSE
14 NC
13 GATE
12 NC
11 NC
10 FB
9
TIMER
Supply Voltage (V
CC
) .................................. – 0.3 to 44V
SENSE, PWRGD ......................................... – 0.3 to 44V
GATE .......................................................... – 0.3 to 50V
FB, UV, OPEN ............................................. – 0.3 to 44V
OV .............................................................. – 0.3 to 18V
RETRY ........................................................ – 0.3 to 15V
TIMER ..................................................... – 0.3V to 4.3V
Maximum Input Current (TIMER) ....................... 100µA
Operating Temperature
LT4254C ................................................. 0°C to 70°C
LT4254I ............................................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART NUMBER
LT4254CGN
LT4254IGN
GN PART MARKING
4254
4254I
GN PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Note:
NC = No Connect
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 24V unless otherwise noted.
SYMBOL
V
CC
I
CC
UVLH
ELECTRICAL CHARACTERISTICS
PARAMETER
Operating Voltage
Operating Current
Undervoltage Threshold
Hysteresis
UV Input Current
Overvoltage Threshold
Hysteresis
OV Input Current
Open-Circuit Voltage Threshold (V
CC
– V
SENSE
)
OPEN Output Low Voltage
Leakage Current
SENSE Pin Trip Voltage (V
CC
– V
SENSE
)
SENSE Pin Input Current
GATE Pull-Up Current
GATE Pull-Down Current
External N-Channel Gate Drive (Note 2)
FB Voltage Threshold
FB Hysteresis Voltage
PWRGD Output Low Voltage
CONDITIONS
●
MIN
10.8
TYP
1.9
MAX
36
3
4.04
0.55
–1
–3
4.04
0.55
1
5
0.5
1.3
1
25
60
70
– 63
80
12.5
12.5
4.04
4.65
0.60
0.4
1.0
UNITS
V
mA
V
V
µA
µA
V
V
µA
mV
V
V
µA
mV
mV
µA
µA
mA
V
V
V
V
V
V
V
4254fb
V
CC
Low-to-High Transition
UV = 4.5V
UV = 0V
V
CC
Low-to-High Transition
0V
≤
OV < 6.5V
●
3.96
0.25
4
0.4
–0.1
–1.5
V
UVHYS
I
INUV
V
OVHL
V
OVHYS
I
INOV
V
OPEN
V
OLOPEN
I
INOPEN
V
SENSETRIP
I
INSNS
I
PU
I
PD
∆V
GATE
V
FB
V
FBHYS
V
OLPGD
●
3.96
0.25
4
0.4
0.1
3.5
0.20
0.75
0.1
●
2
I
O
= 2mA
I
O
= 5mA
V
OPEN
= 5V
FB = 0V
FB
≥
2V
Charge Pump On,
∆V
GATE
= 7V
Any Fault, V
GATE
= 3V
V
GATE
– V
CC
, 12V
≤
V
CC
≤
20V
20V
≤
V
CC
≤
36V
FB High-to-Low Transition
FB Low-to-High Transition
I
O
= 1.6mA
I
O
= 5mA
●
●
●
●
●
●
●
5.5
40
–15
40
4.5
10
3.96
4.20
0.3
12
50
40
– 35
60
8.8
11
4
4.45
0.45
0.25
0.63
2
U
W
U
U
W W
W
LT4254
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 24V unless otherwise noted.
SYMBOL
I
PWRGD
I
INFB
I
TIMERPU
I
TIMERPD
V
THTIMER
D
TIMER
V
RETRY(TH)
I
INRTR
t
PHLUV
t
PLHUV
t
PHLFB
t
PLHFB
t
PHLSENSE
PARAMETER
PWRGD Pin Leakage Current
FB Input Current
TIMER Pull-Up Current
TIMER Pull-Down Current
TIMER Shut-Down Threshold Voltage
Duty Cycle (RETRY Mode)
RETRY Threshold
RETRY Input Current
UV Low to GATE Low
UV High to GATE High
FB Low to PWRGD Low
FB High to PWRGD High
(V
CC
– V
SENSE
) High to GATE Low
V
CC
– V
SENSE
= 275mV
RETRY = GND
C
GATE
= 100pF
C
GATE
= 100pF
C
TIMER
= 10nF
CONDITIONS
V
PWRGD
= 36V
FB = 4.5V
●
●
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
–1
– 60
1
4.3
1.5
0.4
–120
TYP
0.1
–0.1
– 120
3
4.65
3
0.8
–85
1.7
6
0.8
3.2
2.5
MAX
10
–180
5
5
4.5
1.2
–40
UNITS
µA
µA
µA
µA
V
%
V
µA
µs
µs
µs
µs
4
µs
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
An internal clamp limits the GATE pin to a maximum of 11V above
V
CC
(under normal operating conditions). Driving this pin to a voltage
beyond the clamp voltage may damage the part.
TYPICAL PERFOR A CE CHARACTERISTICS
SENSE Pin Regulation Voltage
vs Temperature, FB = 0V
17
SENSE REGULATION VOLTAGE (mV)
15
13
SENSE REGULATION VOLTAGE (mV)
11
9
7
5
–50
–25
50
I
CC
(mA)
50
25
75
0
TEMPERATURE (°C)
U W
100
4254 G01
SENSE Pin Regulation Voltage
vs Temperature, FB > 2V
60
3.0
I
CC
vs V
CC
T
A
= 25°C
55
2.5
2.0
45
1.5
125
40
–50 –25
1.0
75
0
25
50
TEMPERATURE (°C)
100
125
10
15
20
25
V
CC
(V)
30
35
40
4254 G03
4254 G02
4254fb
3
LT4254
TYPICAL PERFOR A CE CHARACTERISTICS
I
CC
vs Temperature
FB THRESHOLD VOLTAGE LOW-TO-HIGH (V)
2.0
V
CC
= 24V
V
CC
= 36V
1.8
4.44
4.42
4.40
4.38
4.36
4.34
–50 –25
FB THRESHOLD VOLTAGE HIGH-TO-LOW (V)
I
CC
(mA)
1.6
V
CC
= 10.8V
1.4
1.2
1.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
FB Pin Hysteresis vs Temperature
480
460
440
FB HYSTERESIS (mV)
I
GATE
PULL-UP CURRENT (µA)
0
–10
–15
–20
–25
–30
I
GATE
PULL-DOWN CURRENT (mA)
420
400
380
360
340
320
300
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
∆V
GATE
vs Temperature
12
11
∆V
GATE
(V
GATE
– V
CC
) (V)
V
CC
= 18V
∆V
GATE
(V
GATE
– V
CC
) (V)
10
9
8
7
6
5
4
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
V
CC
= 12V
∆V
GATE
(V
GATE
– V
CC
) (V)
V
CC
= 10.8V
4
U W
100
4254 G04
FB Pin Threshold Voltage (Low-
to-High) vs Temperature
4.46
4.02
4.01
4.00
3.99
3.98
3.97
FB Pin Threshold Voltage (High-
to-Low) vs Temperature
125
50
25
75
0
TEMPERATURE (°C)
100
125
3.96
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4254 G05
4254 G06
GATE Pin Pull-Up Current
vs Temperature
80
75
70
65
60
55
50
45
–5
GATE Pin Pull-Down Current
vs Temperature
–35
–40
–45
–50
–25
0
25
75
50
TEMPERATURE (°C)
100
125
40
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
4254 G07
4254 G08
4254 G09
∆V
GATE
vs Temperature
13.0
12.5
12.0
V
CC
= 24V, 36V
11.5
V
CC
= 20V
11.0
10.5
10.0
–50 –25
∆V
GATE
vs V
CC
14
12
10
8
6
4
2
0
T
A
= 25°C
50
25
75
0
TEMPERATURE (°C)
100
125
10
15
20
25
V
CC
(V)
30
35
40
" #" /
4254 G10
4254 G11
4254fb
LT4254
TYPICAL PERFOR A CE CHARACTERISTICS
TIMER Pin Pull-Up Current
vs Temperature
–80
TIMER PULL-DOWN CURRENT (µA)
TIMER PULL-UP CURRENT (µA)
4.0
–90
–100
–110
–120
–130
–140
–150
–50 –25
TIMER PULL-DOWN CURRENT (µA)
50
25
0
75
TEMPERATURE (°C)
TIMER Shutdown Threshold
vs Temperature
TIMER SHUTDOWN THRESHOLD VOLTAGE (V)
5.0
T
A
= 25°C
4.8
UV THRESHOLD VOLTAGE HIGH-TO-LOW (V)
TIMER PULL-UP CURRENT (µA)
4.6
4.4
4.2
4.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
UV Threshold Voltage (Low-to-
High) vs Temperature
UV THRESHOLD VOLTAGE LOW-TO-HIGH (V)
4.02
4.01
4.00
3.99
3.98
3.97
3.96
–50
–25
500
450
OV THRESHOLD VOLTAGE (LOW-TO-HIGH) (V)
UV HYSTERESIS (mV)
50
25
75
0
TEMPERATURE (°C)
U W
100
4254 G13
TIMER Pin Pull-Down Current
vs Temperature
3.4
3.5
TIMER Pin Pull-Down Current
vs V
CC
T
A
= 25°C
3.2
3.0
2.8
2.6
2.4
2.2
2.0
3.0
2.5
2.0
1.5
1.0
0.5
0
– 50
– 25
0
125
75
50
25
TEMPERATURE (°C)
100
125
10
15
20
25
V
CC
(V)
30
35
40
" #" / #
4254 G14
TIMER Pin Pull-Up Current vs V
CC
–116
3.66
UV Threshold Voltage (High-to-
Low) vs Temperature
3.65
3.64
3.63
–118
–120
3.62
3.61
–122
3.60
3.59
3.58
– 50
– 25
0
50
75
25
TEMPERATURE (°C)
100
125
–124
100
125
–126
10
15
20
25
V
CC
(V)
30
35
40
4254 G17
4254 G16
4254 G18
UV Hysteresis vs Temperature
4.02
4.01
4.00
3.99
3.98
3.97
OV Threshold Voltage (Low-to-
High) vs Temperature
400
350
300
250
200
–50
–25
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
3.96
–50
–25
50
25
75
0
TEMPERATURE (°C)
100
125
4254 G19
4254 G20
4257 G21
4254fb
5
