LT4256-3
Positive High Voltage
Hot Swap Controller
with Open-Circuit Detect
FEATURES
s
s
s
s
s
s
DESCRIPTIO
s
s
s
s
Allows Safe Board Insertion and Removal from a
Live Backplane
Controls Supply Voltage from 10.8V to 80V
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
Open MOSFET Detection
1% Over and Undervoltage Detection Accuracy
Available in a 16-Lead SSOP Package
The LT
®
4256-3 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 80V. The part features an open-circuit detect
(OPEN) output that indicates abnormally low load current
conditions.
The LT4256-3 also 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, the PWRGD output asserts low and the LT4256-3
either automatically restarts after a time-out delay or
latches off until the UV pin is cycled low (depending on the
status of the RETRY pin).
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.
The LT4256-3 is available in a 16-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
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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
SMAT70A
(SHORT PIN)
64.9k
UV
0.01µF
4.02k
OV
4.02k
OPEN
TIMER
GND
33nF
GND
V
CC
0.020Ω
48V, 2A Hot Swap Controller
IRF540
+
CMPZ5241BS
11V
SENSE
10Ω
GATE
LT4256-3
V
OUT
FB
100Ω
10nF
36.5k
51k
C
L
V
OUT
48V
2A
V
IN
50V/DIV
4.02k
INRUSH
CURRENT
500mA/DIV
PWRGD
50V/DIV
PWRGD
4256 TA01
PWRGD
UV = 36V
OV = 73V
PWRGD = 40V
RETRY
U
TM
U
U
LT4256-3 Start-Up Behavior
CONTACT BOUNCE
V
OUT
50V/DIV
2.5ms/DIV
42563 TA02
42563f
1
LT4256-3
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 V
OUT
11 NC
10 FB
9
TIMER
Supply Voltage (V
CC
) ................................ – 0.3 to 100V
SENSE, PWRGD ....................................... – 0.3 to 100V
GATE Voltage (Note 2) .................... – 0.3V to V
CC
+ 10V
GATE Maximum Current ..................................... 200µA
V
OUT
.......................................................... –3V to 100V
FB, UV, OPEN ............................................. – 0.3 to 44V
OV .............................................................. – 0.3 to 18V
RETRY ........................................................ – 0.3 to 15V
TIMER Voltage ......................................... – 0.3V to 4.3V
Maximum Input Current (TIMER) ....................... 100µA
Operating Temperature
LT4256-3C ............................................. 0°C to 70°C
LT4256-3I ......................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT4256-3CGN
LT4256-3IGN
GN PART MARKING
42563
42563I
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 130°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
UVRTH
V
OVLH
V
OVHYS
I
INOV
V
OPEN
V
OLOPEN
I
INOPEN
V
SENSETRIP
I
INSNS
I
PU
I
PD
I
PDL
∆V
GATE
∆V
GATEL
PARAMETER
Operating Voltage
Operating Current
Undervoltage Threshold
Hysteresis
UV Input Current
Fault Latch Reset Threshold Voltage
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
V
OUT
Pull-Down Current, Fault Condition
External N-Channel Gate Drive (Note 2)
External N-Channel Gate Drive, Fault Condition
I
O
= 2mA
I
O
= 5mA
V
OPEN
= 5V
FB = 0V
FB
≥
2V
V
SENSE
= V
CC
Charge Pump On,
∆V
GATE
= 7V
Any Fault, V
GATE
> V
OUT
Any Fault, V
GATE
= V
OUT
+
∆V
GATEL
,
V
OUT
= 48V
V
GATE
– V
OUT
, 10.8V
≤
V
CC
≤
20V
20V
≤
V
CC
≤
80V
V
GATE
– V
OUT
, V
OUT
= 48V
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
q
MIN
10.8
TYP
1.8
MAX
80
3.9
4.04
0.55
–1
–3
1.2
4.04
0.55
1
6.5
0.5
1.3
1
22
65
70
– 55
80
UNITS
V
mA
V
V
µA
µA
V
V
V
µA
mV
V
V
µA
mV
mV
µA
µA
mA
µA
V
CC
Low-to-High Transition
UV
≥
1.2V
UV = 0V
q
3.96
0.25
4
0.4
–0.1
–1.5
q
0.4
3.96
0.25
0.85
4
0.4
0.1
3
0.20
0.75
0.1
V
CC
Low-to-High Transition
0V
≤
OV < 7V
q
q
1.5
7
45
–16
40
14
55
40
– 30
62
130
4.5
10
8.8
11.6
–2
12.5
12.8
42563f
2
U
V
V
V
W
U
U
W W
W
LT4256-3
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
FB
V
FBHYS
V
OLPGD
I
PWRGD
I
INFB
I
TIMERPU
I
TIMERPD
V
THTIMER
D
TIMER
V
RETRYTH
I
INRTR
t
PHLUV
t
PLHUV
t
PHLFB
t
PLHFB
t
PHLSENSE
PARAMETER
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 Shutdown Threshold
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
I
O
= 1.6mA
I
O
= 5mA
V
PWRGD
= 80V
FB = 4.5V
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
FB High-to-Low Transition
FB Low-to-High Transition
q
q
MIN
3.95
4.20
0.3
TYP
3.99
4.45
0.45
0.25
0.60
0.1
–0.1
MAX
4.03
4.65
0.60
0.4
1.0
1
–1
–145
5
5
4.5
1.2
–130
3
9
2
5
3
UNITS
V
V
V
V
V
µA
µA
µA
µA
V
%
V
µA
µs
µs
µs
µs
µs
– 85
1.5
4.3
1.5
0.4
– 115
3
4.65
3
0.85
–87
1.7
6
0.8
3.2
1
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
Specifications are at T
A
= 25°C unless otherwise noted.
SENSE Regulation Voltage
vs Temperature
58
FB > 2V
SENSE REGULATION VOLTAGE (mV)
53
I
CC
(mA)
2.0
1.5
1.0
20
I
CC
(mA)
48
15
FB = 0V
10
–50
–25
0
25
50
TEMPERATURE (°C)
U W
75
100
42563 G01
I
CC
vs V
CC
3.5
3.0
2.0
2.5
I
CC
vs Temperature
V
CC
= 48V
2.5
1.5
1.0
0.5
0
10
20
30
50
40
V
CC
(V)
60
70
80
0.5
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G03
42563 G02
42563f
3
LT4256-3
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at T
A
= 25°C unless otherwise noted.
GATE Pull-Up Current
vs Temperature
0
GATE PULL-DOWN CURRENT (mA)
–5
GATE PULL-UP CURRENT (µA)
–10
–15
–20
–25
–30
–35
–40
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G04
60
59
58
57
56
–50
I
GATE
(mA )
V
GATE
– V
OUT
Voltage
vs Temperature
14
12
V
GATE
– V
OUT
VOLTAGE (V)
10
8
6
4
2
0
–50
V
CC
= 12V
V
CC
= 18V
14.0
13.5
V
GATE
– V
OUT
VOLTAGE (V)
13.0
12.0
11.5
11.0
10.5
V
CC
= 80V
I
TIMER
(µA)
V
CC
= 10.8V
–25
0
25
50
TEMPERATURE (°C)
TIMER Currents vs V
CC
5.0
TIMER SHUTDOWN THRESHOLD (V)
PULL-DOWN CURRENT
2.5
0
I
TIMER
(µA)
I
UV
(µA)
–80
PULL-UP CURRENT
–100
–120
–140
10
20
30
50
40
V
CC
(V)
60
4
U W
75
42563 G06
GATE Pull-Down Current
vs Temperature
63
62
61
60
50
40
30
20
10
0
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G05
GATE Pull-Down Capability vs V
CC
Below Minimum Operating Voltage
0
2
4
6
V
CC
(V)
8
10
12
42563 G17
V
GATE
– V
OUT
Voltage
vs Temperature
5.0
TIMER Currents vs Temperature
PULL-DOWN CURRENT
2.5
0
V
CC
= 20V
V
CC
= 48V
–80
12.5
–100
–120
–140
–50
PULL-UP CURRENT
100
10.0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G07
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G08
TIMER Shutdown Threshold
vs Temperature
5.4
5.2
5.0
4.8
4.6
4.4
–1.0
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
UV Current vs UV Voltage
4.2
0
–50
–1.2
–1.4
70
80
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G10
0
1
2
3
10 20 30 40 50
V
UV
(V)
4
42563 G18
42563 G09
42563f
LT4256-3
TYPICAL PERFOR A CE CHARACTERISTICS
Specifications are at T
A
= 25°C unless otherwise noted.
UV Thresholds vs Temperature
4.1
L-H THRESHOLD
4.0
UV THRESHOLDS (V)
3.9
200
150
OV THRESHOLDS (V)
4.0
3.9
3.8
3.7
H-L THRESHOLD
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G11
I
OV
(µA)
3.8
3.7
H-L THRESHOLD
3.6
3.5
–50
OPEN Output Voltage vs I
OPEN
10
OPEN THRESHOLD VOLTAGE (mV)
9
8
7
V
OPEN
(V)
6
5
4
3
2
1
0
0
2
4
6
8
I
OPEN
(mA)
10
12
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
V
PWRGD
(V)
FB Thresholds vs Temperature
4.5
4.4
FB THRESHOLDS (V)
4.3
4.2
4.1
4.0
3.9
–50
H-L THRESHOLD
L-H THRESHOLD
0.2
0.1
0
I
FB
(µA)
–25
U W
42563 G13
OV Current vs OV Voltage
250
4.1
OV Thresholds vs Temperature
L-H THRESHOLD
100
50
3.6
3.5
–50
0
5
10
V
OV
(V)
15
20
42563 G19
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G12
OPEN Threshold Voltage
vs Temperature
6
5
4
3
2
1
0
PWRGD Output Voltage
vs I
PWRGD
V
CC
– V
SENSE
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
42563 G14
0
2
4
6
8
I
PWRGD
(mA)
10
12
42563 G15
FB Current vs FB Voltage
–0.1
–0.2
–0.3
–0.4
0
25
50
TEMPERATURE (°C)
75
100
42563 G16
0
10
20
30
V
FB
(V)
40
50
42563 G20
42563f
5
Microchip MCU
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