safely inserted and removed from a live backplane. Using
an external N-channel pass transistor, board supply voltage
and inrush current are ramped up at an adjustable rate.
An I
2
C interface and onboard ADC allows for monitoring
of board current, voltage, power, energy and fault status.
The device features analog foldback current limiting to
limit the MOSFET power to a constant value. A wide input
voltage operating range comfortably allows applications
from 2.9V to 33V.
The LTC4281 is well suited to high power applications
because the precise monitoring capability and accurate
current limiting reduce the extremes in which both loads
and power supplies must safely operate. Non-volatile
configuration allows for flexibility in the autonomous
generation of alerts and response to faults.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
n
n
n
n
n
n
n
n
n
n
n
Allows Safe Board Insertion Into Live Backplane
12-/16-Bit ADC with ±0.7% Total Unadjusted Error
Monitors Current, Voltage, Power and Energy
Internal EEPROM for Nonvolatile Configuration
Wide Operating Voltage Range: 2.9V to 33V
I
2
C/SMBus Digital Interface (Coexists with PMBus
Devices)
12V Gate Drive for Lower MOSFET R
DS(ON)
Programmable Current Limit with 2% Accuracy
MOSFET Power Limiting with Current Foldback
Continuously Monitors MOSFET Health
Stores Minimum and Maximum Measurements
Alerts When Alarm Thresholds Exceeded
Reboots on I
2
C Command
Input Overvoltage/Undervoltage Protection
Three General Purpose Input/Outputs
Internal ±5% or External Timebases
28-Pin 4mm
×
5mm QFN Package
Enterprise Servers and Data Storage Systems
Network Routers and Switches
Base Stations
Platform Management
applicaTions
n
n
n
n
Typical applicaTion
12V, 65A Plug-In Board Resident Application
12V
SMCJ15CA
CONNECTOR 2
CONNECTOR 1
V
DD
ADC
+
SENSE
+
NC
NC
UV
OV
SDAI
SDAO
SCL
ALERT
ADR0
ADR1
ADR2
ON INTV
CC
4.7µF
0.5m
Start-Up Waveforms
+
V
OUT
12V
65A
10
SENSE
–
ADC
–
GATE
SOURCE
FB
GPIO1
GPIO2
GPIO3
TIMER
WP CLKIN CLKOUT GND
4281 TA01a
V
DD
10V/DIV
CONTACT BOUNCE
NC
POWER
GOOD
GP
GP
∆V
GATE
10V/DIV
50ms DE-BOUNCE
V
SOURCE
10V/DIV
GPIO1(PG)
10V/DIV
20ms/DIV
4281 TA01b
SDA
SCL
ALERT
LTC4281
NC
12V
100k
GND
BACKPLANE PLUG-IN
BOARD
10nF
NC
4281f
For more information
www.linear.com/LTC4281
1
LTC4281
absoluTe MaxiMuM raTings
(Notes 1, 2)
pin conFiguraTion
TOP VIEW
SENSE
+
SENSE
–
SDAO
ADC
+
ADC
–
22 GATE
21 SOURCE
20 FB
29
19 GND
18 GPIO1
17 GPIO2
16 GPIO3
15
ALERT
9 10 11 12 13 14
ADR0
ADR1
ADR2
SDAI
SCL
V
DD
UV
ON 1
OV 2
GND 3
WP 4
INTV
CC
5
TIMER 6
CLKOUT 7
CLKIN 8
Supply Voltage V
DD
.................................... –0.3V to 45V
Input Voltages
GATE – SOURCE (Note 3) ...................... –0.3V to 10V
SENSE
+
, ADC
+
, SENSE
–
...... V
DD
– 4.5V to V
DD
+ 0.3V
ADC
–
........................................... –0.3V to V
DD
+ 0.3V
SOURCE................................................. –0.3V to 45V
ADR0-2, TIMER .....................–0.3V to INTV
CC
+ 0.3V
CLKIN. .................................................. –0.3V to 5.5V
UV, OV, FB, WP, ON, GPIO1-3,
SCL, SDAI ............................................. .–0.3V to 45V
Output Voltages
GATE, GPIO1-3,
ALERT,
SDAO................ –0.3V to 45V
CLKOUT ................................... –0.3 to INTV
CC
+ 0.3V
Output Current INTV
CC
(V
DD
> 4V) ........................25mA
Operating Ambient Temperature Range
LTC4281C ................................................ 0°C to 70°C
LTC4281I..............................................–40°C to 85°C
Storage Temperature Range .................. –65°C to 125°C
28 27 26 25 24 23
UFD PACKAGE
28-LEAD (4mm
×
5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 29) PCB CONNECTION OPTIONAL
orDer inForMaTion
LEAD FREE FINISH
LTC4281CUFD#PBF
LTC4281IUFD#PBF
TAPE AND REEL
LTC4281CUFD#TRPBF
LTC4281IUFD#TRPBF
PART MARKING*
4281
4281
PACKAGE DESCRIPTION
28-Lead (4mm
×
5mm) Plastic QFN
28-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
4281f
2
For more information
www.linear.com/LTC4281
LTC4281
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
DD
= 12V unless otherwise noted.
SYMBOL
Supplies
V
DD
I
DD
V
DD(UVL)
V
DD(HYST)
INTV
CC
INTV
CC(UVL)
INTV
CC(HYST)
Current Limit
∆V
SENSE
Current Limit Voltage DAC Zero-Scale
Current Limit Voltage DAC Full-Scale
Current Limit Voltage DAC INL
Fast Current Limit Comparator Offset
I
SENSE
–
I
SENSE
+
Gate Drive
∆V
GATE
I
GATE
Gate Drive (V
GATE
– V
SOURCE
) (Note 3)
Gate Pull-Up Current
Gate Pull-Down Current
Gate Fast Pull-Down Current
t
PHL(FAST)
V
GATE
Comparator Inputs
I
IN
V
TH-R
V
TH-F
V
TH-R
V
TH-F
V
TH
V
HYST
V
TH
V
TH
V
HYST
t
PHL
UV, OV, FB, ON WP Input Current
V
DD
, SOURCE Rising Threshold Voltages for
UV, Power Good (Note 6)
V
DD
, SOURCE Falling Threshold Voltages for
UV, Power Good (Note 6)
V
DD
Rising Threshold Voltages of OV (Note 6)
V
DD
Falling Threshold Voltages of OV (Note 6)
UV, OV, FB, ON Rising Threshold
UV, OV, FB, ON Hysteresis
FET-Bad FAULT V
DS
Threshold
WP Pin Threshold Voltage
WP Pin Hysteresis
Turn-Off Propagation Delay
ON, UV, OV Turn-Off
Falling
V = 1.2V
5%
10%
15%
5%
10%
15%
5%
10%
15%
5%
10%
15%
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
PARAMETER
Input Supply Range
Input Supply Current
Input Supply Undervoltage Lockout
CONDITIONS
l
l
MIN
2.9
TYP
MAX
33
UNITS
V
mA
V
mV
V
V
mV
mV
mV
mV
mV
LSB
mV
µA
µA
V
µA
mA
A
µs
V
µA
%
%
%
%
%
%
%
%
%
%
%
%
V
mV
mV
V
mV
µs
4281f
3.5
2.65
15
3.1
2.45
50
12.25
3.4
32.88
8.81
–0.05
2.7
40
3.3
2.6
110
12.5
3.75
34.37
10.31
0
0
0
0
10
–15
0.5
0.3
5
90
12.5
–20
1.3
0.9
0.5
8
0
–5
–10
–15
–10
–15
–20
10
15
20
5
10
15
1.26
23
150
1.26
2
10
–7.5
–12.5
–17.5
–12.5
–17.5
–22.5
12.5
17.5
22.5
7.5
12.5
17.5
1.28
43
200
1.28
20
25
8
2.75
75
3.5
2.7
175
12.75
4.1
35.87
11.81
0.05
±15
±1
130
13.5
–30
3
3
1
10
±1
–10
–15
–20
–15
–20
–25
15
20
25
10
15
20
1.3
63
270
1.3
35
45
V
DD
Rising
l
l
l
Input Supply Undervoltage Lockout Hysteresis
Internal Regulator Voltage
INTV
CC
Undervoltage Lockout
INTV
CC
Undervoltage Lockout Hysteresis
V
FB
= 1.3V, I
LIM
= 000
V
FB
= 0V, I
LIM
= 000
V
FB
= 1.3V, I
LIM
= 111
V
FB
= 0V, I
LIM
= 111
INTV
CC
Rising
l
l
l
l
l
l
l
l
SENSE
–
Pin Input Current
SENSE
+
Pin Input Current
V
SENSE–
= 12V
V
SENSE+
= 12V
V
DD
= 2.9V to 33V, I
GATE
= –1µA
Gate On, V
GATE
= 0V
Gate Off, V
GATE
= 10V
∆V
SENSE
=100mV,
∆V
GATE
= 10V
∆V
SENSE
=0mV Step to 100mV, C = 10nF
l
l
l
l
l
l
l
l
Overcurrent to GATE Low
∆V
GATE
FET Off Threshold
For more information
www.linear.com/LTC4281
3
LTC4281
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
DD
= 12V unless otherwise noted.
SYMBOL
t
PHL
t
D
Crystal Oscillator
V
TH
f
MAX
I
CLKIN
I
CLKOUT
V
TH
V
HYST
V
OL
I
OH
t
PHL
CLKIN Pin Rising Threshold
Maximum CLKIN Pin Input Frequency
CLKIN Pin Input Current
CLKOUT Pin Output Current
GPIO,
ALERT
Threshold
GPIO,
ALERT
Hysteresis
GPIO,
ALERT
Output Low Voltage
GPIO,
ALERT
Leakage Current
Stress Condition to GPIO2 Low Propagation
Delay
TIMER Low Threshold
TIMER High Threshold
I
TIMER
Doc
I
SOURCE
I
ADC
–
I
ADC
+
ADC
RESOLUTION
V
OS
TUE
ADC Resolution (No Missing Codes)
ADC Offset Error, Percent of Full-Scale
ADC Total Unadjusted Error (Note 5)
∆V
ADC
, SOURCE, V
DD
, GPIO
POWER
ENERGY (Internal Timebase)
ENERGY (Crystal/External Timebase)
∆V
ADC
, SOURCE, V
DD
, GPIO
POWER
ENERGY (Internal Timebase)
ENERGY (Crystal/External Timebase)
∆V
ADC
= ADC
+
– ADC
–
SOURCE/V
DD
= 24V Range
SOURCE/V
DD
= 12V Range
SOURCE/V
DD
= 5V Range
SOURCE/V
DD
= 3.3V Range
GPIO
l
l
l
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
PARAMETER
Fast Turn On Propagation Delay
Debounced Turn On Propagation Delay
CONDITIONS
ON Pin Turn On
UV, OV Turn On
l
l
MIN
10
45
0.4
–10
–150
1.26
2
TYP
25
50
1
MAX
45
55
2
25
10
150
UNITS
µs
ms
V
MHz
µA
µA
V
mV
V
µA
µs
V = 0V to 3.3V
V = 0V to 3.3V
Falling
I = 3mA
V = 33V
GATE Low or V
DS
= 1V
l
l
GPIO Pin Functions
l
l
l
l
l
1.28
20
0.3
0
1.31
35
0.4
±1
35
5
13
TIMER Pin Functions
V
TH
Falling
Rising
V = 0V
V = 1.3V
l
l
l
l
l
0.11
1.25
–18
3
0.045
70
0.15
1.28
–20
5
0.08
180
0
25
0.19
1.31
–22
7
0.11
350
±1
110
V
V
µA
µA
%
µA
µA
µA
Bits
TIMER Pull-Up Current
TIMER Pull-Down Current
Overcurrent Auto-Retry Duty Cycle
SOURCE Input Current
ADC
–
Input Current
ADC
+
Input Current
SOURCE, ADC Pin Currents
V = 12V
V
ADC
– = 33V
V
ADC
+ = 33V
l
l
l
12/16
±0.25
±0.7
±1.0
±5.1
±1.0
±0.7
±1.0
±5.1
±1.0
40
33.28
16.64
8.32
5.547
1.28
0.2
±5
%
%
%
%
%
%
%
%
%
mV
V
V
V
V
V
LSB
FSE
ADC Full-Scale Error
V
FS
ADC Full-Scale Range
INL
ADC Integral Nonlinearity, 12-Bit Mode
4281f
4
For more information
www.linear.com/LTC4281
LTC4281
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
DD
= 12V unless otherwise noted.
SYMBOL
V
FS
PARAMETER
Alarm Threshold Full-Scale Range
(256 •
V
LSB
)
CONDITIONS
∆V
ADC
SOURCE/V
DD
= 24V
SOURCE/V
DD
= 12V
SOURCE/V
DD
= 5V
SOURCE/V
DD
= 3.3V
GPIO
V = 1.28V
12-Bit Mode, Internal Clock
16-Bit Mode, Internal Clock
l
l
l
elecTrical characTerisTics
MIN
TYP
40
33.28
16.64
8.32
5.547
1.28
MAX
UNITS
mV
V
V
V
V
V
MΩ
R
GPIO
f
CONV
I
2
C Interface
V
ADR(H)
I
ADR(IN,Z)
V
ADR(L)
I
ADR(IN)
V
SDA,SCL(TH)
I
SDA,SCL(OH)
V
SDAO(OL)
I
SDAO(OH)
f
SCL(MAX)
t
BUF(MIN)
t
HD,STA(MIN)
t
SU,STA(MIN)
t
SU,STO(MIN)
t
HD,DATI(MIN)
t
HD,DATO
t
SU,DAT(MIN)
t
SP(MAX)
C
X
t
D(STUCK)
Endurance
Retention
t
WRITE
GPIO ADC Sampling Resistance
Conversion Rate
1
14.5
0.906
INTV
CC
– 0.8
0.2
1.5
2
15.26
0.954
INTV
CC
– 0.5
0.5
1.7
0.3
0
16
1
INTV
CC
– 0.2
±3
0.8
±80
2.0
±1
0.4
±1
Hz
Hz
V
µA
V
µA
V
µA
V
µA
kHz
ADRn Input High Threshold
ADRn Allowable Leakage in Open State
ADRn Input Low Threshold
ADRn Input Current
SDAI, SCL Input Threshold
SDAI, SCL Input Current
SDAO, Output Low Voltage
SDAO, Pin Input Leakage Current
Maximum SCL Clock Frequency
Bus Free Time Between STOP/START Condition
Hold Time After (Repeated) START Condition
Repeated START Condition Set-Up Time
STOP Condition Set-Up Time
Data Hold Time (Input)
Data Hold Time (Output)
Data Set-Up Time
Maximum Suppressed Spike Pulse Width
SCL, SDA Input Capacitance
I
2
C Stuck Bus Timeout
(Notes 7, 8)
(Notes 7, 8)
Write Operation Time
(Note 4)
SCL, SDA = 5.0V
I = 3mA
V
SDAO
= 33V
ADR = 0V, ADR = INTV
CC
l
l
l
l
l
l
l
l
I
2
C Interface Timing
l
l
l
l
l
l
l
l
l
l
l
400
1000
0.12
30
30
140
30
1.3
600
600
600
100
900
600
250
10
35
µs
us
ns
ns
ns
ns
ns
ns
pF
ms
Cycles
Years
300
50
25
10,000
20
1
500
30
110
30
EEPROM Characteristics
l
l
l
2.2
4
ms
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 pins are positive. All voltages are referenced to
GND unless otherwise specified.
Note 3:
An internal clamp limits the GATE pin to a minimum of 11V above
SOURCE. Driving this pin to voltages beyond the clamp may damage the
device.
Note 4:
Guaranteed by design and not subject to test.
Note 5:
TUE is the maximum ADC error for any code, given as a
percentage of full scale.
Note 6:
UV, OV and FB internal thresholds are given as a percent
difference from the configured operating voltage.
Note 7:
EEPROM endurance and retention are guaranteed by design,
characterization and correlation with statistical process controls.
Note 8:
EEPROM endurance and retention will be degraded when T
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