Data Sheet
FEATURES
Hot Swap Controller and Digital Power and
Energy Monitor with PMBus Interface
ADM1278
TYPICAL APPLICATION CIRCUIT
4.5V TO 20V
R
SENSE
Q1
HS+
VCC
VCAP
UV
LDO
MO+
MO–
HS–
±0.3% accurate, 12-bit ADC for I
OUT
, V
IN
, V
OUT
, and temperature
320 ns response time to short circuit
Shutdown on detection of FET health fault
Constant power foldback for tighter FET SOA protection
Remote temperature sensing with programmable warning
and shutdown thresholds
Resistor-programmable 5 mV to 25 mV V
SENSE
current limit
Programmable start-up current limit
1% accurate UV, OV, and PWRGD thresholds
Split hot swap and power monitor inputs to allow additional
external ADC filtering
Reports power and energy consumption over time
Peak detect registers for current, voltage, and power
PROCHOT power throttling capability
PMBus fast mode compliant interface
5 mm × 5 mm, 32-lead LFCSP
+ –
×50
I
SENSE
ADM1278-1
CHARGE
PUMP
V
CP
GATE
DRIVE/
LOGIC
TIMEOUT
GATE
TEMP
PWGIN
1.0V
+
1.0V
–
1.0V
OV
–
+
ISET
PSET
ISTART
REF
SELECT
1.0V
HS–
+
–
CURRENT-
LIMIT
CONTROL
V
CBOS
I
OUT
+
–
VOUT
TIMER
TIMER TIMEOUT
HS+
I
SENSE
VOUT
TEMP
12-BIT
ADC
LOGIC
AND
PMBus
APPLICATIONS
Servers
Power monitoring and control/power budgeting
Telecommunication and data communication equipment
RETRY
ANALOG
VOUT
PGND
GND
PWRGD
FAULT
ENABLE
GPO2/ALERT2
GPO1/ALERT1/CONV
SCL
SDA
ADR1
ADR2
CSOUT
12198-001
Figure 1.
GENERAL DESCRIPTION
The
ADM1278
is a hot swap controller that allows a circuit board
to be removed from or inserted into a live backplane. It also features
current, voltage, power, and temperature readback via an integrated
12-bit analog-to-digital converter (ADC), accessed using a PMBus™
interface. The load current is measured using an internal current
sense amplifier that measures the voltage across a sense resistor
in the power path via the HS+ and HS− pins. A default current
limit of 20 mV is set, but this limit can be adjusted, if required.
The
ADM1278
limits the current through the sense resistor by
controlling the gate voltage of an external N-channel FET in the
power path, via the GATE pin. The sense voltage, and therefore
the load current, is maintained below the preset maximum. The
ADM1278
protects the external FET by limiting the time that
the FET remains on while the current is at its maximum value.
This current-limit time is set by the choice of capacitor connected
to the TIMER pin. In addition, a constant power foldback scheme
is used to control the power dissipation in the MOSFET during
power-up and fault conditions. The level of this power, along
with the TIMER regulation time, can be set to ensure that the
MOSFET remains within safe operating area (SOA) limits.
In case of a short-circuit event, a fast internal overcurrent
detector responds within 320 ns and signals the gate to shut
down. A 1500 mA pull-down device ensures a fast FET response.
The
ADM1278
features overvoltage (OV) and undervoltage (UV)
protection, programmed using external resistor dividers on the
UV and OV pins. A PWRGD signal can be used to detect when
the output supply is valid, using the PWGIN pin to accurately
monitor the output.
The
ADM1278
is available in a 32-lead LFCSP with a RETRY pin
that can be configured for automatic retry or latch-off when an
overcurrent fault occurs.
Table 1. Model Options
Model
ADM1278-1AA
ADM1278-1A
ADM1278-1B
ADM1278-2A
ADM1278-3A
1
ADC Accuracy
±0.3%
±0.7%
±1.0%
±0.7%
±0.7%
SPI Interface
No
No
No
Yes
No
Enable Pin
1
Active high
Active high
Active high
Active high
Active low
Active high relates to the ENABLE pin, and active low relates to the ENABLE pin.
Rev. A
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ADM1278
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
Typical Application Circuit ............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 3
Specifications..................................................................................... 4
Power Monitoring Accuracy Specifications .............................. 8
Serial Bus Timing Characteristics .............................................. 8
SPI Timing Characteristics (ADM1278-2) ............................... 9
Absolute Maximum Ratings .......................................................... 10
Thermal Characteristics ............................................................ 10
ESD Caution ................................................................................ 10
Pin Configurations and Function Descriptions ......................... 11
Typical Performance Characteristics ........................................... 17
Theory of Operation ...................................................................... 24
Powering the ADM1278 ............................................................ 24
Hot Swap Current Sense Inputs ................................................ 24
Power Monitor Current Sense Inputs ...................................... 25
Current-Limit Reference ........................................................... 25
Setting the Current Limit (ISET).............................................. 26
Setting a Linear Output Voltage Ramp at Power-Up ............. 26
Start-Up Current Limit .............................................................. 27
Constant Power Foldback.......................................................... 28
Timer ............................................................................................ 28
Hot Swap Retry ........................................................................... 29
FET Gate Drive Clamps ............................................................. 29
Fast Response to Severe Overcurrent ...................................... 29
Undervoltage and Overvoltage ................................................. 29
Power Good ................................................................................. 29
FAULT Pin ................................................................................... 29
ENABLE/ENABLE Input .......................................................... 30
Current Sense Output (CSOUT) .............................................. 30
Remote Temperature Sensing ................................................... 30
SPI Interface ................................................................................ 31
V
OUT
Measurement ..................................................................... 32
FET Health .................................................................................. 32
Power Throttling......................................................................... 32
Power Monitor ............................................................................ 32
PMBus Interface ............................................................................. 34
Device Addressing ...................................................................... 34
Data Sheet
SMBus Protocol Usage ............................................................... 34
Packet Error Checking ............................................................... 34
Partial Transactions on I
2
C Bus ................................................ 35
SMBus Message Formats ........................................................... 35
Group Commands ..................................................................... 37
Hot Swap Control Commands ................................................. 37
ADM1278 Information Commands ........................................ 37
Status Commands ...................................................................... 38
GPO and Alert Pin Setup Commands..................................... 38
Power Monitor Commands ...................................................... 39
Warning Limit Setup Commands ............................................ 40
PMBus Direct Format Conversion .......................................... 40
Voltage and Current Conversion Using LSB Values .............. 41
Alert Pin Behavior .......................................................................... 42
Faults and Warnings .................................................................. 42
Generating an Alert ................................................................... 42
Handling/Clearing an Alert ...................................................... 42
SMBus Alert Response Address ............................................... 43
Example Use of SMBus ARA .................................................... 43
Digital Comparator Mode ......................................................... 43
Typical Application Circuits ..................................................... 43
PMBus Command Reference........................................................ 45
Register Details ............................................................................... 46
Operation Register ..................................................................... 46
Clear Faults Register .................................................................. 46
PMBus Capability Register ....................................................... 46
V
OUT
OV Warning Limit Register............................................. 46
V
OUT
UV Warning Limit Register............................................. 47
I
OUT
OC Warning Limit Register .............................................. 47
OT Fault Limit Register ............................................................. 47
OT Warning Limit Register ...................................................... 47
V
IN
OV Warning Limit Register ............................................... 47
V
IN
UV Warning Limit Register ............................................... 48
P
IN
OP Warning Limit Register ................................................ 48
Status Byte Register .................................................................... 48
Status Word Register .................................................................. 49
V
OUT
Status Register ................................................................... 50
I
OUT
Status Register ..................................................................... 50
Input Status Register .................................................................. 50
Temperature Status Register ..................................................... 51
Rev. A | Page 2 of 61
Data Sheet
Manufacturer Specific Status Register ......................................51
Read E
IN
Register .........................................................................52
Read V
IN
Register ........................................................................52
Read V
OUT
Register ......................................................................53
Read I
OUT
Register .......................................................................53
Read Temperature 1 Register .....................................................53
Read P
IN
Register .........................................................................53
PMBus Revision Register ...........................................................53
Manufacturer ID Register ..........................................................54
Manufacturer Model Register....................................................54
Manufacturer Revision Register................................................54
Manufacturer Date Register.......................................................54
Peak I
OUT
Register ........................................................................54
Peak V
IN
Register .........................................................................55
Peak V
OUT
Register ......................................................................55
Power Monitor Control Register ...............................................55
ADM1278
Power Monitor Configuration Register ................................... 55
Alert 1 Configuration Register .................................................. 56
Alert 2 Configuration Register .................................................. 57
Peak Temperature Register ........................................................ 57
Device Configuration Register .................................................. 57
Power Cycle Register .................................................................. 58
Peak P
IN
Register ......................................................................... 59
Read P
IN
(Extended) Register .................................................... 59
Read E
IN
(Extended) Register .................................................... 59
Hysteresis Low Level Register ................................................... 59
Hysteresis High Level Register .................................................. 59
Hysteresis Status Register........................................................... 60
Start-Up I
OUT
Limit Register ...................................................... 60
Outline Dimensions ........................................................................ 61
Ordering Guide ........................................................................... 61
REVISION HISTORY
12/14—Rev. 0 to Rev. A
Changes to Features Section, General Description Section,
and Applications Section .................................................................. 1
Added Table 1, Renumbered Sequentially ..................................... 1
Changes to POWER_CYCLE Command Section ......................37
Change to Power Cycle Register Section......................................58
6/14—Revision 0: Initial Version
Rev. A | Page 3 of 61
ADM1278
SPECIFICATIONS
Data Sheet
V
CC
= 4.5 V to 20 V, V
CC
≥ V
HS+
and V
MO+
, V
HS+
= 2 V to 20 V, V
SENSE_HS
= (V
HS+
− V
HS−
) = 0 V, T
A
= −40°C to +85°C, unless otherwise noted.
Table 2.
Parameter
1
POWER SUPPLY
Operating Voltage Range
Undervoltage Lockout
Undervoltage Hysteresis
Quiescent Current
UV PIN
Input Current
UV Threshold
A Grade and AA Grade
B Grade Only
UV Threshold Hysteresis
UV Glitch Filter
UV Propagation Delay
OV PIN
Input Current
OV Threshold
A Grade and AA Grade
B Grade Only
OV Threshold Hysteresis
OV Glitch Filter
OV Propagation Delay
HS+ AND HS− PINS
Input Current
Input Imbalance
MO+ AND MO− PINS
Input Current
VCAP PIN
Internally Regulated Voltage
A Grade and AA Grade
B Grade Only
ISET PIN
Reference Select Threshold
Internal Reference
Gain of Current Sense
Amplifier
Recommended Maximum
Operating Range
Input Current
GATE PIN
GATE Drive Voltage
Symbol
V
CC
UVLO
I
CC
I
UV
UV
TH
0.99
0.97
45
2
1.0
1.0
60
5
Min
4.5
2.4
90
Typ
Max
20
2.7
120
5.5
50
1.01
1.03
75
7
8
50
0.99
0.97
45
1.5
1.0
1.0
60
3.0
1.01
1.03
75
3.5
4.0
150
5
25
Unit
V
V
mV
mA
nA
V
V
mV
μs
μs
nA
V
V
mV
μs
μs
μA
μA
nA
Test Conditions/Comments
V
CC
rising
GATE on and power monitor running
UV ≤ 3.6 V
UV falling
UV falling
50 mV overdrive
UV low to GATE pull-down active
OV ≤ 3.6 V
OV rising
OV rising
50 mV overdrive
OV high to GATE pull-down active
Per individual pin; V
HS+
, V
HS−
= 20 V
I
ΔSENSE
= (I
+
− I
−
)
Per individual pin; V
MO+
, V
MO−
= 20 V
UV
HYST
UV
GF
UV
PD
I
OV
OV
TH
OV
HYST
OV
GF
OV
PD
I
SENSEx
I
ΔSENSE
I
MO±
V
VCAP
2.68
2.66
V
ISETRSTH
V
CLREF
AV
CSAMP
V
ISET
I
ISET
ΔV
GATE
10
8
7
−20
45
5
750
1.35
2.7
2.7
1.5
1
50
2.72
2.74
1.65
V
V
V
V
V/V
V
nA
0 µA ≤ I
VCAP
≤ 100 µA; C
VCAP
= 1 μF
0 µA ≤ I
VCAP
≤ 100 µA; C
VCAP
= 1 μF
If V
ISET
> V
ISETRSTH
, an internal 1 V reference (V
CLREF
) is used
Accuracies included in total sense voltage accuracies
Accuracies included in total sense voltage accuracies
5 mV to 25 mV V
SENSE
current limit
V
ISET
≤ V
VCAP
Maximum voltage on the gate is always clamped to ≤31 V
ΔV
GATE
= V
GATE
− V
OUT
20 V ≥ V
CC
≥ 8 V; I
GATE
≤ 5 μA
V
HS+
= V
CC
= 5 V; I
GATE
≤ 5 μA
V
HS+
= V
CC
= 4.5 V; I
GATE
≤ 1 μA
V
GATE
= 0 V
V
GATE
≥ 2 V; V
ISET
= 1.0 V; (V
HS+
− V
HS−
) = 30 mV
V
GATE
≥ 2 V
V
GATE
≥ 12 V; V
CC
≥ 12 V
V
CC
= 0 V, V
GATE
= 2 V
0.25
1.25
100
12
GATE Pull-Up Current
GATE Pull-Down Current
Regulation
Slow
Fast
GATE Holdoff Resistance
I
GATEUP
I
GATEDN
I
GATEDN_REG
I
GATEDN_SLOW
I
GATEDN_FAST
14
10
9
−30
75
15
2250
V
V
V
μA
μA
mA
mA
Ω
60
10
1500
20
Rev. A | Page 4 of 61
Data Sheet
Parameter
1
HOT SWAP SENSE VOLTAGE
Hot Swap Sense Voltage
Current Limit
A Grade and AA Grade
B Grade Only
Constant Power Inactive
A Grade and AA Grade
Symbol
V
SENSECL
19.75
19.6
24.75
19.75
14.75
24.6
19.6
14.6
20
20
25
20
15
25
20
15
20.25
20.4
25.25
20.25
15.25
25.4
20.4
15.4
mV
mV
mV
mV
mV
mV
mV
mV
Min
Typ
Max
Unit
Test Conditions/Comments
ADM1278
B Grade Only
Constant Power Active
A Grade and AA Grade
9.25
4.65
1.7
9
4.6
1.4
V
ISTARTCL
4.7
3.7
4.5
3.5
V
ISTARTCL_CLAMP
1.6
1.4
0.6
2
2
0.88
2.4
2.6
1.12
mV
mV
mV
5
4
5
4
5.3
4.3
5.5
4.5
mV
mV
mV
mV
10
5
2
10
5
2
10.75
5.35
2.3
11
5.4
2.6
mV
mV
mV
mV
mV
mV
B Grade Only
V
ISET
> 1.65 V; V
GATE
= (V
HS+
+ 3 V); I
GATE
= 0 μA
V
ISET
> 1.65 V; V
GATE
= (V
HS+
+ 3 V); I
GATE
= 0 μA
V
GATE
= (V
HS+
+ 3 V); I
GATE
= 0 μA; V
DS
= (HS−) − V
OUT
V
ISET
= 1.25 V; V
DS
< 2 V
V
ISET
= 1.0 V; V
DS
< 2 V
V
ISET
= 0.75 V; V
DS
< 2 V
V
ISET
= 1.25 V; V
DS
< 2 V
V
ISET
= 1.0 V; V
DS
< 2 V
V
ISET
= 0.75 V; V
DS
< 2V
FET power limit = (V
PSET
× 8)/(50 × R
SENSE
); constant power
active when V
DS
> (V
PSET
× 8)/I
SET
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 4 V
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 8 V
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 20 V
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 4 V
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 8 V
V
ISET
> 1.65 V; V
PSET
= 0.25 V; V
DS
= 20 V
STRT_UP_IOUT_LIM = 3; V
ISET
> 1.65 V
V
ISTART
= 0.2 V
STRT_UP_IOUT_LIM = 3; V
ISET
> 1.65 V
V
ISTART
= 0.2 V
V
ISTART
= 0 V or STRT_UP_IOUT_LIM = 0
V
ISTART
= 0 V or STRT_UP_IOUT_LIM = 0
Circuit breaker trip voltage, V
CB
= V
SENSECL
− V
CBOS
Start-Up Current Limit
A Grade and AA Grade
B Grade Only
Start-Up Current-Limit Clamp
A Grade and AA Grade
B Grade Only
Circuit Breaker Offset
SEVERE OVERCURRENT
Voltage Threshold
A Grade and AA Grade
V
CBOS
V
SENSEOC
B Grade Only
Short Glitch Filter Duration
Long Glitch Filter Duration
(Default)
Response Time
Short Glitch Filter
Long Glitch Filter
ISTART PIN
Active Range
Gain of Current Sense Amplifier
Input Current
TIMER PIN
TIMER Pull-Up Current
Power-On Reset (POR)
Overcurrent (OC) Fault
23
28
38
43
20
25
35
40
100
530
25
30
40
45
25
30
40
45
27
32
42
47
30
35
45
50
220
900
mV
mV
mV
mV
mV
mV
mV
mV
ns
ns
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (125%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (150%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (200%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; default at power-up (225%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (125%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (150%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; optional select PMBus (200%)
V
ISET
> 1.65 V; V
PSET
> 1.1 V; default at power-up (225%)
V
SENSE_HS
step = 18 mV to (2 mV above V
SENSEOC_MAX
)
V
SENSE_HS
step = 18 mV to (2 mV above V
SENSEOC_MAX
)
200
630
0.1
AV
CSAMP
I
ISTART
50
320
1000
1.25
100
ns
ns
V
V/V
nA
V
SENSE_HS
step = 18 mV to (2 mV above V
SENSEOC_MAX
)
V
SENSE_HS
step = 18 mV to (2 mV above V
SENSEOC_MAX
)
Tie ISTART to VCAP to disable start-up current limit
Accuracies included in total sense voltage accuracies
V
ISTART
≤ V
VCAP
I
TIMERUPPOR
I
TIMERUPFLT
−2
−57
−3
−60
−4
−63
µA
µA
Initial power-on reset; V
TIMER
= 0.5 V
Overcurrent fault; 0.2 V ≤ V
TIMER
≤ 1 V
Rev. A | Page 5 of 61
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