LT4256-1/LT4256-2
Positive High Voltage
Hot Swap Controllers
FEATURES
s
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Allows Safe Board Insertion and Removal from a
Live Backplane
Controls Supply Voltage from 10.8V to 80V
Foldback Current Limiting
Overcurrent Fault Detection
Drives an External N-Channel MOSFET
Programmable Supply Voltage Power-Up Rate
Undervoltage Protection
Latch Off Operation Mode (LT4256-1)
Automatic Retry (LT4256-2)
Available in an 8-Pin SO Package
The LT
®
4256-1/LT4256-2 are high voltage Hot Swap
controllers that allow a board to be safely inserted and
removed from a live backplane. An internal driver drives an
external N-channel MOSFET switch to control supply
voltages ranging from 10.8V to 80V.
The LT4256-1/LT4256-2 features an adjustable analog
foldback current limit. If the supply remains in current limit
for more than a programmable time, the N-channel
MOSFET shuts off and the PWRGD output asserts low. The
LT4256-2 automatically restarts after a time-out delay.
The LT4256-1 latches 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
protection.
The LT4256 can be used as an upgrade to LT1641 designs.
See Table 1 on page 14 for upgraded specifications.
The LT4256-1 and LT4256-2 are available in an 8-pin SO
package that is pin compatible with the LT1641.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
APPLICATIO S
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s
s
Hot Board Insertion
Electronic Circuit Breaker/Power Bussing
Industrial High Side Switch/Circuit Breaker
24V/48V Industrial/Alarm Systems
Ideally Suited for 12V, 24V and 48V Distributed
Power Systems
48V Telecom Systems
TYPICAL APPLICATIO
V
IN
48V
0.02Ω
SMAT70A
(SHORT PIN)
8
64.9k
1
0.1µF
UV
V
CC
7
SENSE
48V, 2A Hot Swap Controller
IRF530
CMPZ5241B
11V
10Ω
6
100Ω
10nF
36.5k
27k
C
L
V
OUT
48V
2A
V
IN
50V/DIV
V
OUT
50V/DIV
GATE
LT4256-1/
LT4256-2
FB
8.06k
2
4.02k
INRUSH
CURRENT
500mA/DIV
PWRGD
4256 TA01
PWRGD
5
GND
33nF
TIMER
GND
4
3
UV = 36V
PWRGD = 40V
PWRGD
50V/DIV
2.5ms/DIV
4256 TA02
U
TM
U
U
LT4256 Start-Up Behavior
425612f
1
LT4256-1/LT4256-2
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
UV 1
FB 2
PWRGD 3
GND 4
8
7
6
5
V
CC
SENSE
GATE
TIMER
Supply Voltage (V
CC
) ................................ – 0.3 to 100V
Input Voltage (SENSE, PWRGD) ............... – 0.3 to 100V
Input Voltage (GATE) (Note 2) ........ – 0.3V to V
CC
+ 10V
Maximum Input Current (GATE) ......................... 200µA
Input Voltage (FB, UV) ................................ – 0.3 to 44V
Input Voltage (TIMER) ............................. – 0.3V to 4.3V
Maximum Input Current (TIMER) ....................... 100µA
Operating Temperature
LT4256C ................................................. 0°C to 70°C
LT4256I ............................................. – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
LT4256-1CS8
LT4256-1IS8
LT4256-2CS8
LT4256-2IS8
S8 PART MARKING
42561
42561I
42562
42562I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 110°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 48V unless otherwise noted.
SYMBOL
V
CC
I
CC
V
UVLH
V
UVHYS
I
INUV
V
SENSETRIP
I
INSNS
I
PU
I
PD
∆V
GATE
V
FB
V
FBHYS
V
OLPGD
I
PWRGD
I
INFB
I
TIMERPU
I
TIMERPD
V
THTIMER
D
TIMER
PARAMETER
Operating Voltage
Operating Current
Undervoltage Threshold
Hysteresis
UV Input 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
PWRGD Pin Leakage Current
FB Input Current
TIMER Pull-Up Current
TIMER Pull-Down Current
TIMER Shut-Down Threshold
Duty Cycle (RETRY Mode)
C
TIMER
= 10nF
I
O
= 1.6mA
I
O
= 5mA
V
PWRGD
= 80V
FB = 4.5V
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
q
MIN
10.8
TYP
1.8
MAX
80
3.9
4.04
0.55
–1
–3
22
65
70
– 55
80
12.5
12.8
4.03
4.65
0.6
0.4
1
1
–1
–145
5
5
4.5
UNITS
V
mA
V
V
µA
µA
mV
mV
µA
µA
mA
V
V
V
V
V
V
V
µA
µA
µA
µA
V
%
V
CC
Low-to-High Transition
UV
≥
1.2V
UV = 0V
FB = 0V
FB
≥
2V
V
SENSE
= V
CC
Charge Pump On,
∆V
GATE
= 7V
Any Fault, V
GATE
= 3V
V
GATE
– V
CC
, 10.8V
≤
V
CC
≤
20V
20V
≤
V
CC
≤
80V
FB High-to-Low Transition
FB Low-to-High Transition
q
3.96
0.25
4
0.4
–0.1
–1.5
q
q
5.5
45
–16
40
4.5
10
3.95
4.2
0.3
14
55
40
– 30
62
8.8
11.6
3.99
4.45
0.45
0.25
0.6
0.1
–0.1
q
q
q
q
q
– 85
1.5
4.3
1.5
– 115
3
4.65
3
425612f
2
U
W
U
U
W W
W
LT4256-1/LT4256-2
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 48V unless otherwise noted.
SYMBOL
t
PHLUV
t
PLHUV
t
PHLFB
t
PLHFB
t
PHLSENSE
PARAMETER
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
C
GATE
= 0
CONDITIONS
MIN
TYP
1.7
6
0.8
3.2
1
MAX
3
9
2
5
3
UNITS
µs
µs
µs
µs
µs
ELECTRICAL CHARACTERISTICS
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 minimum of 10V above
V
CC
. Driving this pin to a voltage beyond the clamp voltage may damage
the part.
TYPICAL PERFOR A CE CHARACTERISTICS
otherwise noted.
UV Thresholds vs Temperature
4.1
L-H THRESHOLD
4.0
UV THRESHOLDS (V)
3.9
3.8
3.7
H-L THRESHOLD
3.6
3.5
–50
SENSE PIN REGULATION VOLTAGE (mV)
58
FB > 2V
I
CC
(mA)
FB = 0V
–25
0
25
50
TEMPERATURE (°C)
I
CC
vs Temperature
2.5
V
CC
= 48V
4.5
4.4
PWRGD THRESHOLDS (V)
4.3
4.2
4.1
4.0
2.0
I
CC
(mA)
1.5
V
PWRGD
(V)
1.0
0.5
0
–50
–25
0
25
50
TEMPERATURE (°C)
U W
75
4256 G01
Specifications are at T
A
= 25°C unless
SENSE Pin Regulation Voltage
vs Temperature
3.5
3.0
2.5
I
CC
vs V
CC
53
48
2.0
1.5
1.0
20
15
0.5
0
100
10
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G02
10
20
30
50
40
V
CC
(V)
60
70
80
4256 G03
PWRGD Thresholds
vs Temperature
6
L-H THRESHOLD
5
4
3
2
H-L THRESHOLD
1
0
PWRGD Output Voltage
vs I
PWRGD
75
100
4256 G04
3.9
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G05
0
2
4
6
8
I
PWRGD
(mA)
10
12
4256 G06
425612f
3
LT4256-1/LT4256-2
TYPICAL PERFOR A CE CHARACTERISTICS
otherwise noted.
GATE Pin Pull-Up Current
vs Temperature
0
GATE PIN PULL-DOWN CURRENT (mA)
GATE PIN PULL-UP CURRENT (µA)
–5
–10
–15
–20
–25
–30
–35
–40
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G07
I
UV
(µA)
V
GATE
– V
CC
Voltage
vs Temperature
14
12
V
GATE
– V
CC
VOLTAGE (V)
10
V
CC
= 12V
8
6
4
2
0
–50
V
CC
= 10.8V
V
CC
= 18V
14.0
13.5
V
GATE
– V
CC
VOLTAGE (V)
13.0
12.0
11.5
11.0
10.5
V
CC
= 80V
V
CC
= 20V
V
CC
= 48V
I
TIMER
(µA)
–25
0
25
50
TEMPERATURE (°C)
TIMER Pin Currents vs V
CC
5.0
TIMER SHUTDOWN THRESHOLD (V)
2.5
0
I
TIMER
(µA)
–80
PULL-UP CURRENT
–100
–120
–140
10
20
4
U W
75
4256 G10
Specifications are at T
A
= 25°C unless
GATE Pin Pull-Down Current
vs Temperature
63
62
61
UV Pin Current vs UV Pin Voltage
0.4
0.2
0
–0.2
60
59
58
57
56
–50
–0.4
–0.6
–0.8
–1.0
–1.2
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G08
–1.4
0
1
2
3
4
20
V
UV
(V)
30
40
50
4256 G09
V
GATE
– V
CC
Voltage
vs Temperature
10
5
0
–80
TIMER Pin Currents
vs Temperature
PULL-DOWN CURRENT
12.5
–100
–120
–140
–50
PULL-UP CURRENT
100
10.0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G11
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G12
Timer Shutdown Threshold
vs Temperature
5.4
5.2
5.0
4.8
4.6
4.4
4.2
0
–50
PULL-DOWN CURRENT
30
50
40
V
CC
(V)
60
70
80
4256 G13
–25
0
25
50
TEMPERATURE (°C)
75
100
4256 G14
425612f
LT4256-1/LT4256-2
TYPICAL PERFOR A CE CHARACTERISTICS
otherwise noted.
FB Pin Current vs FB Pin Voltage
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
0
10
20
30
V
FB
(V)
40
50
4256 G15
I
GATE
(mA )
I
FB
(µA)
U W
Specifications are at T
A
= 25°C unless
Gate Pull-Down Capability vs V
CC
Below Minimum Operating Voltage
60
50
40
30
20
10
0
0
2
4
6
V
CC
(V)
8
10
12
4256 G16
425612f
5
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