LTC2945
Wide Range
I2C Power Monitor
FEATURES
n
n
n
n
n
n
n
n
n
n
n
n
n
DESCRIPTION
Rail-to-Rail Input Range: 0V to 80V
Wide Input Supply Range: 2.7V to 80V
Shunt Regulator for Supplies >80V
Δ∑ ADC with less than ±0.75% Total Unadjusted Error
12-Bit Resolution for Current and Voltages
Internal Multiplier Calculates 24-Bit Power Value
Stores Minimum and Maximum Values
Alerts When Limits Exceeded
Additional ADC Input Monitors an External Voltage
Continuous Scan and Snapshot Modes
Shutdown Mode with IQ < 80µA
Split SDA for Opto-Isolation
Available in 12-Lead 3mm × 3mm QFN and MSOP
Packages
The LTC®2945 is a rail-to-rail system monitor that measures current, voltage, and power. It features an operating
range of 2.7V to 80V and includes a shunt regulator for
supplies above 80V to allow flexibility in the selection of
input supply. The current measurement range of 0V to
80V is independent of the input supply. An onboard 0.75%
accurate 12-bit ADC measures load current, input voltage
and an auxiliary external voltage. A 24-bit power value is
generated by digitally multiplying the measured 12-bit load
current and input voltage data. Minimum and maximum
values are stored and an overrange alert with programmable thresholds minimizes the need for software polling.
Data is reported via a standard I2C interface. Shutdown
mode reduces power consumption to 20µA.
The LTC2945 I2C interface includes separate data input
and output pins for use with standard or opto-isolated I2C
connections. The LTC2945-1 has an inverted data output
for use with inverting opto-isolator configurations.
APPLICATIONS
Telecom Infrastructure
Industrial
n Automotive
n Consumer
n
n
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.
TYPICAL APPLICATION
Wide Range Power Monitor with Onboard ADC and I2C
SENSE+
SENSE–
VDD
0.1µF
NINE I2C
ADDRESSES
TO
LOAD
LTC2945
INTVCC
ALERT
SCL
ADR1
SDAI
ADR0
SDAO
ADIN
GND
I2C
INTERFACE
MEASURED
VOLTAGE
ADC DNL (LSB)
VIN
4V TO 80V
ADC Differential
Nonlinearity (ADIN)
ADC Integral Nonlinearity
(ADIN)
0.3
0.3
0.2
0.2
0.1
0.1
ADC INL (LSB)
0.02Ω
0.0
–0.1
–0.2
0.0
–0.1
–0.2
2945 TA01
–0.3
0
1024
2048
CODE
3072
4096
2945 TA01a
–0.3
0
1024
2048
CODE
3072
4096
2945 TA01b
2945fb
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1
LTC2945
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
VDD Voltage............................................... –0.3V to 100V
SENSE+ Voltage............................................–1V to 100V
SENSE– Voltage......–1V or SENSE+ – 1V to SENSE+ + 1V
INTVCC Voltage (Note 3)............................ –0.3V to 5.9V
ADR1, ADR0, ADIN, ALERT, SDAO, SDAO
Voltage.......................................................... –0.3V to 7V
INTVCC Clamp Current............................................35mA
SCL, SDAI Voltages (Note 4)...................... –0.3V to 5.9V
SCL, SDAI Clamp Current.........................................5mA
Operating Temperature Range
LTC2945C................................................. 0°C to 70°C
LTC2945I..............................................–40°C to 85°C
LTC2945H........................................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10sec)
MS Package Only............................................... 300°C
PIN CONFIGURATION
LTC2945
SENSE –
SENSE+
VDD
TOP VIEW
TOP VIEW
12 11 10
INTVCC 1
13
ADR1 2
ADR0 3
ALERT
8
SDAO
7
SDAI
VDD
INTVCC
ADR1
ADR0
ADIN
GND
6
UD PACKAGE
12-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, qJA = 58.7°C/W
EXPOSED PAD (Pin 13) PCB GND CONNECTION OPTIONAL
LTC2945-1
1
2
3
4
5
6
12
11
10
9
8
7
SENSE+
SENSE–
ALERT
SDAO
SDAI
SCL
MS PACKAGE
12-LEAD PLASTIC MSOP
TJMAX = 125°C, qJA = 135°C/W
SCL
5
GND
ADIN
4
9
SENSE –
SENSE+
VDD
TOP VIEW
TOP VIEW
12 11 10
INTVCC 1
13
ADR1 2
ADR0 3
ALERT
8
SDAO
7
SDAI
VDD
INTVCC
ADR1
ADR0
ADIN
GND
6
SCL
5
GND
ADIN
4
9
UD PACKAGE
12-LEAD (3mm × 3mm) PLASTIC QFN
TJMAX = 125°C, qJA = 58.7°C/W
EXPOSED PAD (Pin 13) PCB GND CONNECTION OPTIONAL
1
2
3
4
5
6
12
11
10
9
8
7
SENSE+
SENSE–
ALERT
SDAO
SDAI
SCL
MS PACKAGE
12-LEAD PLASTIC MSOP
TJMAX = 125°C, qJA = 135°C/W
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2
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LTC2945
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2945CUD#PBF
LTC2945CUD#TRPBF
LFWK
12-Lead (3mm × 3mm) Plastic QFN
0°C to 70°C
LTC2945IUD#PBF
LTC2945IUD#TRPBF
LFWK
12-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC2945HUD#PBF
LTC2945HUD#TRPBF
LFWK
12-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LTC2945CUD-1#PBF
LTC2945CUD-1#TRPBF
LFYX
12-Lead (3mm × 3mm) Plastic QFN
0°C to 70°C
LTC2945IUD-1#PBF
LTC2945IUD-1#TRPBF
LFYX
12-Lead (3mm × 3mm) Plastic QFN
–40°C to 85°C
LTC2945HUD-1#PBF
LTC2945HUD-1#TRPBF
LFYX
12-Lead (3mm × 3mm) Plastic QFN
–40°C to 125°C
LTC2945CMS#PBF
LTC2945CMS#TRPBF
2945
12-Lead Plastic MSOP
0°C to 70°C
LTC2945IMS#PBF
LTC2945IMS#TRPBF
2945
12-Lead Plastic MSOP
–40°C to 85°C
LTC2945HMS#PBF
LTC2945HMS#TRPBF
2945
12-Lead Plastic MSOP
–40°C to 125°C
LTC2945CMS-1#PBF
LTC2945CMS-1#TRPBF
29451
12-Lead Plastic MSOP
0°C to 70°C
LTC2945IMS-1#PBF
LTC2945IMS-1#TRPBF
29451
12-Lead Plastic MSOP
–40°C to 85°C
LTC2945HMS-1#PBF
LTC2945HMS-1#TRPBF
29451
12-Lead Plastic MSOP
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD is from 4V to 80V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SUPPLIES
VDD
VDD Supply Voltage Range
l
4
l
2.7
VINTVCC
INTVCC Supply Voltage Range
5.9
V
IDD
VDD Supply Current
VDD = 48V, INTVCC Open
Shutdown
l
l
0.8
40
1.2
70
mA
µA
ICC
INTVCC Supply Current
INTVCC = VDD = 5V
Shutdown, INTVCC = VDD = 5V
l
l
0.6
20
0.9
80
mA
µA
ICCSRC
INTVCC Linear Regulator Output Current
VDD = 7V
l
VCC
INTVCC Linear Regulator Voltage
7V < VDD < 80V, ILOAD = 1mA (C-, I-Grade)
7V < VDD < 80V, ILOAD = 1mA (H-Grade)
l
l
ΔVCC
INTVCC Linear Regulator Load Regulation
7V < VDD < 80V, ILOAD = 1mA to 10mA
l
4.5
4.5
VCCZ
INTVCC Shunt Regulator Voltage
VDD = 48V, ICC = 1mA
l
ΔVCCZ
INTVCC Shunt Regulator Load Regulation
VDD = 48V, ICC = 1mA to 35mA
l
5.9
VCC(UVL)
INTVCC Supply Undervoltage Lockout
INTVCC Rising, VDD = INTVCC
l
2.2
VDD(UVL)
VDD Supply Undervoltage Lockout
VDD Rising, INTVCC Open (C-, I-Grade)
VDD Rising, INTVCC Open (H-Grade)
l
l
VDDI2C(RST)
VDD I2C Logic Reset
VDD Falling, INTVCC Open (C-, I-Grade)
VDD Falling, INTVCC Open (H-Grade)
VCCI2C(RST)
INTVCC I2C Logic Reset
INTVCC Falling, VDD = INTVCC
80
V
–10
mA
5
5
5.5
5.7
V
V
100
200
mV
6.3
6.7
V
250
mV
2.6
2.69
V
2.9
2.6
3.2
3.2
3.5
3.5
V
V
l
l
2
1.7
2.5
2.5
V
V
l
1.5
1.8
V
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3
LTC2945
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD is from 4V to 80V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
80
V
100
150
2
µA
µA
SENSE INPUTS
VCM
SENSE+, SENSE– Common Mode Voltage
ISENSE+(HI)
48V SENSE+ Input Current
ISENSE–(HI)
48V SENSE– Input Current
SENSE+, SENSE–, VDD = 48V
Shutdown
l
l
20
1
µA
µA
ISENSE+(LO)
0V SENSE+ Source Current
SENSE+, SENSE– = 0V VDD = 48V
Shutdown
l
l
–10
–2
µA
µA
ISENSE–(LO)
0V SENSE– Source Current
SENSE+, SENSE– = 0V, VDD = 48V
Shutdown
l
l
–5
±1
µA
µA
RES
Resolution (No missing codes)
(Note 5)
l
12
VFS
Full-Scale Voltage
∆SENSE (Note 7)
VIN
ADIN
l
l
l
101.7
101.7
2.033
LSB
LSB Step Size
∆SENSE
VIN
ADIN
TUE
Total Unadjusted Error (Note 6)
∆SENSE
VIN
ADIN
l
l
l
±0.75
±0.75
±0.75
%
%
%
VOS
Offset Error
∆SENSE
VIN
ADIN
l
l
l
±3.1
±1.5
±1.1
LSB
LSB
LSB
INL
Integral Nonlinearity
∆SENSE
VIN
ADIN
l
l
l
±3
±2
±2
LSB
LSB
LSB
sT
Transition Noise (Note 5)
∆SENSE
VIN
ADIN
fCONV
Conversion Rate (Continuous Mode)
tCONV
Conversion Time (Snapshot Mode)
RADIN
IADIN
l
SENSE+, SENSE–, V
Shutdown
DD = 48V
0
l
l
ADC
Bits
102.4
102.4
2.048
103.1
103.1
2.063
25
25
0.5
mV
V
V
µV
mV
mV
1.2
0.3
10
µVRMS
mVRMS
µVRMS
l
6
7.5
9
Hz
∆SENSE
VIN, ADIN
l
l
60
30
66
33
72
36
ms
ms
ADIN Pin Input Resistance
VDD = 48V, ADIN = 3V
l
3
10
ADIN Pin Input Current
VDD = 48V, ADIN = 3V
l
MΩ
±1
µA
I2C INTERFACE (VDD = 48V)
VADR(H)
ADR0, ADR1 Input High Threshold
l
2.1
2.4
2.7
V
VADR(L)
ADR0, ADR1 Input Low Threshold
l
0.3
0.6
0.9
V
IADR(IN)
ADR0, ADR1 Input Current
±13
µA
ADR0, ADR1 = 0V, 3V
l
IADR(IN,Z)
Allowable Leakage When Open
±7
µA
VOD(OL)
SDAO, SDAO, ALERT Output Low Voltage
ISDAO, ISDAO, IALERT = 8mA
l
0.15
0.4
V
ISDA,SCL(IN)
SDAI, SDAO, SDAO, SCL Input Current
SDAI, SDAO, SDAO, SCL = 5V
l
0
±1
µA
VSDA,SCL(TH)
SDAI, SCL Input Threshold
VSDA,SCL(CL)
SDAI, SCL Clamp Voltage
IALERT(IN)
ALERT Input Current
l
l
1.5
1.9
2.2
V
ISDAI, ISCL = 3mA
l
5.9
6.4
6.9
V
ALERT = 5V
l
0
±1
µA
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LTC2945
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VDD is from 4V to 80V unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I2C INTERFACE TIMING
fSCL(MAX)
Maximum SCL Clock Frequency
400
kHz
tLOW
Minimum SCL Low Period
0.65
1.3
µs
tHIGH
Minimum SCL High Period
50
600
ns
tBUF(MIN)
Minimum Bus Free Time Between Stop/Start
Condition
0.12
1.3
µs
tHD,STA(MIN)
Minimum Hold Time After (Repeated) Start
Condition
140
600
ns
tSU,STA(MIN)
Minimum Repeated Start Condition Set-Up
Time
30
600
ns
tSU,STO(MIN)
Minimum Stop Condition Set-Up Time
tHD,DATI(MIN)
Minimum Data Hold Time Input
tHD,DATO(MIN)
Minimum Data Hold Time Output
tSU,DAT(MIN)
Minimum Data Set-Up Time
tSP(MAX)
Maximum Suppressed Spike Pulse Width
tRST
Stuck Bus Reset Time
CX
SCL, SDAI Input Capacitance (Note 5)
30
600
ns
–100
0
ns
600
900
ns
30
100
ns
50
110
250
ns
25
33
300
SCL or SDAI Held Low
5
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
ground, unless otherwise noted.
Note 3: An internal shunt regulator limits the INTVCC pin to a minimum of
5.9V. Driving this pin to voltages beyond 5.9V may damage the part. This
pin can be safely tied to higher voltages through a resistor that limits the
current below 35mA.
ms
10
pF
Note 4: Internal clamps limit the SCL and SDAI pins to a minimum of 5.9V.
Driving these pins to voltages beyond the clamp may damage the part. The
pins can be safely tied to higher voltages through resistors that limit the
current below 5mA.
Note 5: Guaranteed by design and not subject to test.
Note 6:
( ACTUAL CODE −IDEAL CODE) × 100%
TUE =
4096
where IDEAL CODE is derived from a straight line passing through Code 0
at 0V and Theoretical Code of 4096 at VFS.
Note 7: ∆SENSE is defined as VSENSE+ – VSENSE –
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5
LTC2945
TYPICAL PERFORMANCE CHARACTERISTICS
800
VDD Supply Current
70
VDD = 48V, TA = 25°C, unless noted.
VDD Supply Current in Shutdown
600
INTVCC Supply Current
700
650
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
60
750
50
40
30
575
550
525
20
600
0
20
40
60
VDD SUPPLY VOLTAGE (V)
10
80
0
20
40
60
VDD SUPPLY VOLTAGE (V)
2945 G01
5.2
22.5
INTVCC Load Regulation
5.5
12.5
2
3
4
5
VCC SUPPLY VOLTAGE (V)
5.0
4.9
4.8
6
0
2
4
6
LOAD CURRENT (mA)
8
0.1
0.1
–0.3
1024
2048
CODE
3072
4096
2945 G07
0
20
40
60
VDD SUPPLY VOLYAGE (V)
2945 G06
0.02
0.0
–0.1
–0.3
80
ADC Total Unadjusted Error
(ADIN)
–0.2
0
3.0
10
ADC TOTAL UNADJUSTED ERROR (%)
0.2
ADC DNL (LSB)
ADC INL (LSB)
0.2
–0.2
4.0
ADC Differential Nonlinearity
(ADIN)
0.3
–0.1
4.5
2945 G05
0.3
0.0
INTVCC Line Regulation
3.5
2945 G04
ADC Integral Nonlinearity (ADIN)
6
5.0
INTVCC VOLTAGE (V)
15.0
3
4
5
VCC SUPPLY VOLTAGE (V)
2945 G03
5.1
INTVCC VOLTAGE (V)
SUPPLY CURRENT (µA)
20.0
17.5
2
2945 G02
INTVCC Supply Current in
Shutdown
10.0
500
80
0
1024
2048
CODE
3072
4096
2945 G08
0.01
0
–0.01
–0.02
0
1024
2048
CODE
3072
4096
2945 G09
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LTC2945
TYPICAL PERFORMANCE CHARACTERISTICS
ADC Integral Nonlinearity
(∆SENSE)
VDD = 48V, TA = 25°C, unless noted.
ADC Differential Nonlinearity
(∆SENSE)
0.4
ADC Total Unadjusted Error
(∆SENSE)
0.50
ADC TOTAL UNADJUSTED ERROR (%)
0.3
0.2
ADC DNL (LSB)
ADC INL (LSB)
0.2
0.0
0.1
0.0
–0.1
–0.2
–0.2
–0.4
0
1024
2048
CODE
3072
–0.3
4096
0
1024
3072
2048
CODE
2945 G10
4096
0.25
0.00
–0.25
–0.50
0
1024
2048
CODE
3072
2945 G12
2945 G11
SDAO, SDAO, ALERT Loaded
Output Low Voltage
INTVCC Shunt Regulator Load
Regulation
SCL, SDAI Loaded Clamp Voltage
0.4
4096
6.6
6.6
6.5
0.2
INTVCC VOLTAGE (V)
VSDA,SCL(CL) (V)
VSDA,ALERT(OL) (V)
0.3
6.4
6.3
6.2
0.1
6.4
6.2
6.1
0.0
0
2
4
6
ISDA,ALERT (mA)
8
6.0
0.01
10
0.10
1.00
6.0
10.00
0
ILOAD (mA)
2945 G13
10
20
30
VCC SHUNT CURRENT (mA)
2945 G14
SENSE+ Input Current
2945 G15
ADRO, ADR1 Voltage with Current
Sink or Source
SENSE– Input Current
150
40
10
3.0
8
2.5
6
2.0
70
VADR (V)
ISENSE– (µA)
ISENSE+ (µA)
110
4
1.5
2
1.0
0
0.5
30
–10
0
20
40
VSENSE+ (V)
60
80
2945 G16
–2
0
20
40
VSENSE+ (V)
60
80
2945 G17
0.0
–10
–5
0
IADR (µA)
5
10
2945 G18
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7
LTC2945
PIN FUNCTIONS
ADIN: ADC Input. The onboard ADC measures voltages
between 0V and 2.048V. Tie to ground if unused.
ADR1, ADR0: I2C Device Address Inputs. Connecting these
pins to INTVCC, GND or leaving the pins open configures
one of nine possible addresses. See Table 1 in Applications
Information section for details.
ALERT: Fault Alert Output. Open drain logic output that
is pulled to ground after an ADC conversion resulted in
a fault to alert the host controller. A fault alert is enabled
by setting the corresponding bit in the ALERT register
as shown in Table 4. This device is compatible with the
SMBus alert protocol. See Applications Information. Tie
to ground if unused.
EXPOSED PAD (Pin 13, DD Package Only): Exposed pad
may be left open or connected to device ground. For best
thermal performance, connect to a large PCB area.
GND: Device Ground.
INTVCC: Internal Low Voltage Supply Input/Output. This
pin is used to power internal circuitry. It can be configured as a direct input for a low voltage supply, as linear
regulator from higher voltage supply connected to VDD,
or as a shunt regulator. Connect this pin directly to a 2.7V
to 5.9V supply if available. When INTVCC is powered from
an external supply, short the VDD pin to INTVCC. If VDD
is connected to a 4V to 80V supply, INTVCC becomes the
5V output of an internal series regulator that can supply
up to 10mA to external circuitry. For even higher supply
voltages or if a floating topology is desired, INTVCC can
be used as a 6.3V shunt regulator. Connect the supply to
INTVCC through a shunt resistor that limits the current to
less than 35mA. An undervoltage lockout circuit disables
the ADC when the voltage at this pin drops below 2.5V.
Connect a bypass capacitor between 0.1µF and 1µF from
this pin to ground.
SCL: I2C Bus Clock Input. Data at the SDAI pin is shifted
in or out on rising edges of SCL. This pin is driven by an
open-collector output from a master controller. An external
pull-up resistor or current source is required and can be
placed between SCL and VDD or INTVCC. The voltage at
SCL is internally clamped to 6.4V (5.9V minimum)
SDAI: I2C Bus Data Input. Used for shifting in address,
command or data bits. This pin is driven by an opencollector output from a master controller. An external
pull-up resistor or current source is required and can be
placed between SDAI and VDD or INTVCC. The voltage at
SDAI is internally clamped to 6.4V (5.9V minimum)
SDAO: I2C Bus Data Output. Open-drain output used for
sending data back to the master controller or acknowledging
a write operation. An external pull-up resistor or current
source is required.
SDAO: Inverted I2C Bus Data Output. Open-drain output
used for sending data back to the master controller or
acknowledging a write operation. Data is inverted for
convenience of opto-isolation. An external pull-up resistor
or current source is required.
SENSE+: Supply Voltage and Current Sense Input. Used as
a supply and current sense input for the internal current
sense amplifier. The voltage at this pin is monitored by the
onboard ADC with a full-scale input range of 102.4V. See
Figure 16 for recommended Kelvin connection.
SENSE–: Current Sense Input. Connect an external sense
resistor between SENSE+ and SENSE–. The differential
voltage between SENSE+ and SENSE– is monitored by the
onboard ADC with a full-scale sense voltage of 102.4mV.
VDD: High Voltage Supply Input. This pin powers an internal
series regulator with input voltages ranging from 4V to
80V and produces 5V at INTVCC when the input voltage
is above 7V. Connect a bypass capacitor between 0.1µF
and 1µF from this pin to ground if external load is present on the INTVCC pin. The onboard 12-bit ADC can be
configured to monitor the voltage at VDD with a full-scale
input range of 102.4V.
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LTC2945
BLOCK DIAGRAM
SENSE+
VDD
SENSE–
ADR0
ADR1
ALERT
DECODER
+
VSTBY
20X
–
5.7V
VSTBY
GEN
INTV CC
2
IC
735k
SDAO/SDAO
(LTC2945 / LTC2945-1)
VREF = 2.048V
735k
LOGIC
SDAI
VSTBY
12
MUX
6.3V
15k
6.4V
12-BIT ADC
SCL
REGISTERS
15k
6.4V
ADIN
GND
2945 BD
2945fb
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9
LTC2945
TIMING DIAGRAM
SDA
tSU,DAT
tHD,DATO
tHD,DATI
tSU,STA
tSP
tHD,STA
tSP
tBUF
tSU,STO
2945 TD
SCL
tHD,STA
REPEATED START
CONDITION
REPEATED START
CONDITION
STOP
CONDITION
START
CONDITION
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LTC2945
OPERATION
The LTC2945 accurately monitors current, voltage, and
power of any supply rail from 0V to 80V. An internal linear
regulator allows the LTC2945 to operate directly from a
4V to 80V rail, or from an external supply voltage between
2.7V and 5.9V. Quiescent current is less than 0.9mA in
normal operation. Enabling shutdown mode via the I2C
interface reduces the quiescent current to below 80μA.
The LTC2945 includes a shunt regulator for operation from
supply voltages above 80V.
The onboard 12-bit analog-to-digital converter (ADC) runs
either continuously or on-demand using snapshot mode.
In the default continuous scan mode, the ADC repeatedly
measures the differential voltage between SENSE+ and
SENSE– (full-scale 102.4mV) the voltage at the SENSE+
or VDD pin (full-scale 102.4V), and the voltage at the ADIN
pin (full-scale 2.048V). The conversion results are stored
in onboard registers.
In snapshot mode, the LTC2945 performs a single measurement of one selected voltage or current. Snapshot
mode is enabled by setting the snapshot mode enable bit
in the CONTROL register via the I2C interface. A status bit
in the CONTROL register monitors the ADC’s conversion;
when complete, the conversion result is stored in the corresponding data registers.
Onboard logic tracks the minimum and maximum values
for each ADC measurement, calculates power data by
digitally multiplying the stored current and voltage data,
and triggers a user-configurable alert by pulling the ALERT
pin low when the ADC measured value falls outside the
programmed window thresholds. All logic outputs are
stored in onboard registers. The LTC2945 includes an
I2C interface to access the onboard data registers and to
program the alert threshold and control registers. Two
three-state pins, ADR1 and ADR0, are decoded to allow
nine device addresses (see Table 1). The SDA pin is split
into SDAI (input) and SDAO (output, LTC2945) or SDAO
(output, LTC2945-1) to facilitate opto-isolation.
APPLICATIONS INFORMATION
The LTC2945 offers a compact and complete solution for
high- and low-side power monitoring. With an input common mode range of 0V to 80V and a wide input supply
operating voltage range from 2.7V to 80V, this device is
ideal for a large variety of power management applications
including automotive, industrial and telecom infrastructure.
The basic application circuit shown in Figure 1 provides
monitoring of high side current with a 0.02Ω resistor
(5.12A full-scale), input voltage (102.4V full-scale) and an
external voltage (2.048V full-scale), all using an internal
12-bit resolution ADC.
RSNS
0.02Ω
VIN
4V TO 80V
SENSE+
VDD
C2
0.1µF
INTVCC
SENSE–
LTC2945
ADR1
R1
2k
GND
R3
2k
VDD
SDA µP
SDAI
SDAO
ADIN
R2
2k
SCL
SCL
INT
ALERT
ADR0
3.3V
VOUT
VADIN
GND
2945 F01
Figure 1. Monitoring High Side Current and Voltages
Using the LTC2945
Data Converter
The LTC2945 features an onboard, 12-bit Δ∑ ADC that inherently averages input noise over the measurement window.
The ADC continuously monitors three voltages in sequence:
∆SENSE first, VDD or VSENSE+ second, and VADIN third. The
differential voltage between SENSE+ and SENSE– is monitored with 25μV resolution (102.4mV full-scale) to allow
accurate measurement across very low value shunt resistors.
The supply voltage at VDD or SENSE+ is directly measured
with 25mV resolution (102.4V full-scale). The voltage at
the uncommitted ADIN pin is measured with 0.5mV resolution (2.048V full-scale) to allow monitoring of an arbitrary
external voltage. A 12-bit digital word corresponding to
each measured voltage is stored in two adjacent registers
For more information www.linear.com/LTC2945
2945fb
11
LTC2945
APPLICATIONS INFORMATION
out of the six total ADC data registers (∆SENSE MSB/LSB,
VIN MSB/LSB, and ADIN MSB/LSB), with the eight MSBs
in the first register and the four LSBs in the second (see
Table 2). The lowest 4 bits in the LSB registers are set to 0.
These data registers are updated immediately following the
corresponding ADC conversion, giving an effective refresh
rate of 7.5Hz in continuous scan mode.
The data converter also features a snapshot mode which
makes a measurement of a single selected voltage (either
∆SENSE, VDD or VSENSE+, or VADIN). To make a snapshot
measurement, set CONTROL register bit A7 and write the
two-bit code of the desired ADC channel to A6 and A5 (Table
3) using a Write Byte command. When the Write Byte command is completed, the ADC converts the selected voltage
and the Busy Bit (A3 in the CONTROL register) will be set to
indicate that the conversion is in progress. After completing
the conversion, the ADC will halt and the Busy Bit will reset
to indicate that the data is ready. To make another snapshot
measurement, rewrite the CONTROL register.
Flexible Power Supply to LTC2945
The LTC2945 can be externally configured to flexibly derive
power from a wide range of supplies. The LTC2945 includes
an onboard linear regulator to power the low-voltage internal
circuitry connected to the INTVCC pin from high VDD voltages.
The regulator operates with VDD voltages from 4V to 80V,
and produces a 5V output capable of supplying 10mA at the
INTVCC pin when VDD is greater than 7V. The regulator is
disabled when die temperature rises above 150°C, and the
output is protected against accidental shorts. Bypass capacitors between 0.1μF and 1μF at both the VDD and INTVCC pins
are recommended for optimal transient performance. Note
that operation with high VDD voltages can cause significant
power dissipation, and care is required to ensure the operating
junction temperature stays below 125°C. For improved power
dissipation, use the QFN package and solder the exposed pad
to a large copper region for improved thermal resistance.
Figure 2a shows the LTC2945 being used to monitor an input
supply that ranges from 4V to 80V. No secondary supply
is needed since VDD can be connected directly to the input
supply. If the LTC2945 is used to monitor an input supply of
0V to 80V, it can derive power from a wide range secondary
supply connected to the VDD pin as shown in Figure 2b. The
SENSE pins can be biased independent of the part’s supply
voltage. Alternatively, if a low voltage supply is present it
can be connected to the INTVCC pin as shown in Figure 2c
to minimize on-chip power dissipation. When INTVCC is
powered from a secondary supply, connect VDD to INTVCC.
For supply voltages above 80V, the shunt regulator at
INTVCC can be used in both high and low side configurations to provide power to the LTC2945 through an external
shunt resistor, RSHUNT. Figure 3a shows a high side power
monitor with an input monitoring range beyond 80V in a
high side shunt regulator configuration. The device ground
is separated from ground through RSHUNT and clamped at
6.3V below the input supply. Note that due to the different
ground levels, the I2C signals from the part need to be level
shifted for communication with other ground referenced
components. The bus voltage can be measured with the
ADIN pin as shown in Figure 3a. To mitigate the effect of VBE
mismatch in the PNP mirror, select R1 (=R2) to drop 1V at
the operating voltage. For details on the power calculation,
refer to the Power Calculation and Configuration section.
Figure 3b shows a high side rail-to-rail power monitor which
derives power from a greater than 80V secondary supply.
The voltage at INTVCC is clamped at 6.3V above ground in a
low side shunt regulator configuration to power the part. In
low side power monitors, the device ground and the current
sense inputs are connected to the negative terminal of the
input supply and the ADIN pin can be used to measure the
bus voltage with an external resistive divider as shown in
Figure 3c. The low side shunt regulator configuration allows
operation with input supplies above 80V by clamping the
voltage at INTVCC. RSHUNT should be sized according to the
following equation:
VS(MAX ) – 5.9V
VS(MIN) – 6.7V
≤RSHUNT ≤
35mA
1mA + ILOAD(MAX )
where VS(MAX) and VS(MIN) are the operating maximum
and minimum of the supply. ILOAD(MAX) is the maximum
(1)
external current load that is connected to the shunt regulator. The shunt resistor must also be rated to safely dissipate
the worst-case power. As an example, consider the –48V
Telecom System where the supply operates from –36V to
–72V and the shunt regulator is used to supply an external
load up to 4mA. RSHUNT needs to be between 1.9k and
5.9k according to the above equation, and for reduced
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LTC2945
APPLICATIONS INFORMATION
RSNS
VIN
4V TO 80V
SENSE+
RSNS
VIN
>80V
R1
VOUT
SENSE–
R2
INTVCC SENSE+
Q1
LTC2945
VDD
ADIN
LTC2945
R3
INTVCC
C2
SENSE–
R4
GND
2945 F03a
GND
RSHUNT
2945 F02a
Figure 3a. LTC2945 Derives Power
Through High-Side Shunt Regulator
Figure 2a. LTC2945 Derives Power from
the Supply Being Monitored
RSNS
VIN
0V TO 80V
SENSE+
SENSE–
SENSE+
>80V
VDD
4V TO 80V
RSNS
VIN
0V TO 80V
VOUT
RSHUNT
VOUT
SENSE–
INTVCC
VDD
LTC2945
LTC2945
C2
INTVCC
C2
GND
GND
2945 F02b
2945 F03b
Figure 2b. LTC2945 Derives Power from
a Wide Range Secondary Supply
Figure 3b. LTC2945 Derives Power Through Low-Side
Shunt Regulator in High-Side Current Sense Topology
GND
RSHUNT
RSNS
VIN
0V TO 80V
SENSE+
VOUT
INTVCC
SENSE–
VDD
INTVCC
2.7V TO 5.9V
VDD
R1
C2
GND
LTC2945
C2
LTC2945
ADIN
R2
SENSE–
SENSE+
GND
2945 F03a
VNEG
>–80V
2945 F02c
Figure 2c. LTC2945 Derives Power from
a Low Voltage Secondary Supply
RSNS
VOUT
Figure 3c. LTC2945 Derives Power Through Low-Side
Shunt Regulator in Low-Side Current Sense Topology
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13
LTC2945
APPLICATIONS INFORMATION
GND
VDD
INTVCC
C2
GND
LTC2945
SENSE–
VNEG
–4V TO –80V
SENSE+
2945 F03b
RSNS
VOUT
Figure 3d. LTC2945 Derives Power from the Supply
Being Monitored in Low-Side Current Sense Topology
power dissipation, a larger resistance is advantageous.
The worst-case power dissipated in an RSHUNT of 5.4k is
calculated to be 0.8W. So, three 0.5W rated 1.8k resistors
in series would suffice for this example.
If the supply input is nominally below 80V and transient
is limited to below 100V, the shunt resistor is not required
and VDD can be connected to GND of the supply as shown
in Figure 3d.
Supply Undervoltage Lockout
During power-up, the internal I2C logic and the ADC are
enabled when either VDD or INTVCC rises above its undervoltage lockout threshold. During power-down, the ADC is
disabled when VDD and INTVCC fall below their respective
undervoltage lockout thresholds. The internal I2C logic is
reset when VDD and INTVCC fall below their respective I2C
reset thresholds.
The onboard linear regulator is disabled in shutdown mode
to conserve power. If low IQ mode is not required and the
regulator is used to power I2C bus-related circuitry such as
opto-couplers or pull-ups, ensure bit A1 in the CONTROL
register is masked off during software development. In such
applications, the user is advised that accidentally disabling
the regulator would prevent I2C communication from the
master and cause the LTC2945 to disengage from the system.
The LTC2945 would then have to be reset by cycling its power
to come out of shutdown. It is recommended that external
regulators be used in such applications if powering down
the LTC2945 is desirable. Quiescent current drops below
80µA in shutdown mode with the internal regulator disabled.
Power Calculation and Configuration
The LTC2945 calculates power by multiplying the measured
current with the measured voltage. In continuous mode, the
differential voltage between SENSE+ and SENSE– is measured
to obtain load current data. The supply voltage data for multiplication can be selected between VDD, SENSE+, or ADIN.
SENSE+ is selected by default as it is normally connected
to the supply voltage. In negative supply voltage systems
such as shown in Figure 3d, the device ground (GND pin
of LTC2945) and SENSE– are connected to the supply and
VDD measures the supply voltage at GND with respect to the
device ground. For negative supply voltages of more than
80V, use external resistors to divide down the voltage to suit
the ADIN measurement range. In the CONTROL register,
• write bits A2=1, A0=1 to select SENSE+ (Default)
• write bits A2=0, A0=1 to select VDD
Shutdown Mode
• write bits A2=1, A0=0 to select ADIN
The LTC2945 includes a low quiescent current shutdown
mode, controlled by bit A1 in the CONTROL register
(Table 3). Setting A1 puts the part in shutdown mode,
powering down the ADC and internal reference. The internal
I2C bus remains active, and although the ADR1 and ADR0
pins are disabled, the device will retain the most recently
programmed I2C bus address. All on-board registers retain their contents and can be accessed through the I2C
interface. To re-enable ADC conversions, reset bit A1 in
the CONTROL register. The analog circuitry will power up
and all registers will retain their contents.
More details on the CONTROL register can be found in
Table 3.
Once the ADC conversions are complete, a 24-bit power
value is generated by digitally multiplying the 12-bit load
current data with the 12-bit supply voltage data. 1LSB of
power is 1LSB of voltage multiplied by 1LSB of ∆SENSE
(current). The result is held in the three adjacent POWER
registers (Table 2). The POWER registers initialize with
undefined data and subsequently refresh at a frequency
of 7.5Hz in continuous scan mode. In snapshot mode, the
POWER registers are not refreshed.
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LTC2945
APPLICATIONS INFORMATION
Storing Minimum and Maximum Values
The LTC2945 compares each measurement including the
calculated power with the stored values in the respective
MIN and MAX registers for each parameter (Table 2). If
the new conversion is beyond the stored minimum or
maximum values, the MIN or MAX registers are updated
with the new values. The MIN and MAX of the registers are
refreshed at the end of their respective ADC conversions
in both continuous scan mode and snapshot mode. They
are also refreshed if the ADC registers are written via the
I2C bus with values beyond the stored values. To initiate
a new peak hold cycle, write all 1’s to the MIN registers
and all 0’s to the MAX registers via the I2C bus. These
registers will be updated when the next respective ADC
conversion is done.
The LTC2945 also includes MIN and MAX THRESHOLD
registers (Table 2) for the measured parameters including
the calculated power. At power-up, the maximum thresholds are set to all 1’s and minimum thresholds are set to
all 0’s, effectively disabling them. The thresholds can be
reprogrammed to any desired value via the I2C bus.
Fault Alert and Resetting Faults
As soon as a measured quantity falls below the minimum
threshold or exceeds the maximum threshold, the LTC2945
sets the corresponding flag in the STATUS register and
latches it into the FAULT register (see Figure 4). The ALERT
pin is pulled low if the appropriate bit in the ALERT register
is set. More details on the alert behavior can be found in
the Alert Response Protocol section.
An active fault indication can be reset by writing zeros
to the corresponding FAULT register bits or by reading
the FAULT CoR register (Table 2), which clears all FAULT
register bits. All FAULT register bits are also cleared if the
VDD and INTVCC fall below their respective I2C logic reset
threshold. Note that faults that are still present, as indicated in the STATUS registers, will immediately reappear.
I2C Interface
The LTC2945 is a read-write slave device and supports
the SMBus Read Byte, Write Byte, Read Word and Write
Word protocols. The LTC2945 also supports extended
Read and Write commands that allow reading or writing
more than two bytes of data. When using the Read/Write
Word or extended Read and Write commands, the bus
master issues an initial register address and the internal
register address pointer automatically increments by 1
after each byte of data is read or written. After the register
address reaches 31h, it will roll over to 00h and continue
incrementing. A Stop condition resets the register address
pointer to 00h. The data formats for the above commands
are shown in Figures 6 to 11.
I2C Device Addressing
Nine distinct I2C bus addresses are configurable using the
three-state pins ADR0 and ADR1, as shown in Table 1.
ADR0 and ADR1 should be tied to INTVCC, to GND, or left
floating (NC) to configure the lower four address bits.
During low power shutdown, the address select state
is latched into memory powered from standby supply.
Address bits a6, a5 and a4 are permanently set to (110)
and the least significant bit is the R/W bit. In addition, all
LTC2945 devices will respond to a common Mass Write
address (1100 110)b; this allows the bus master to write
to several LTC2945s simultaneously, regardless of their
individual address settings. The LTC2945 will also respond
to the standard ARA address (0001100)b if the Alert pin
is asserted; see the Alert Response Protocol section for
more details. The LTC2945 will not respond to the ARA
address if no alerts are pending.
Start and Stop Conditions
When the I2C bus is idle, both SCL and SDA are in the high
state. A bus master signals the beginning of a transmission
with a Start condition by transitioning SDA from high to
low while SCL stays high. When the master has finished
communicating with the slave, it issues a Stop condition
by transitioning SDA from low to high while SCL stays
high. The bus is then free for another transmission.
The LTC2945 includes an I2C/SMBus-compatible interface to provide access to the onboard registers. Figure 5
shows a general data transfer format using the I2C bus.
2945fb
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15
LTC2945
APPLICATIONS INFORMATION
STATUS
MEASURED
DATA
DIGITAL
COMPARATOR
LOGIC
THRESHOLD
DATA
FAULT
LATCH
ENA_ALERT_RESPONSE
ALERT
RESET
2945 F04
Figure 4. LTC2945 Fault Alert Generation Blocks
SDA
a6 - a0
SCL
b7 - b0
1-7
8
9
1-7
b7 - b0
8
9
1-7
8
9
S
P
START
CONDITION
ADDRESS
R/W
ACK
DATA
ACK
DATA
STOP
CONDITION
ACK
2945 F05
Figure 5. General Data Transfer over I2C
S
ADDRESS W A
COMMAND
1 1 0 a3:a0 0 0
X X b5:b0
FROM MASTER TO SLAVE
FROM SLAVE TO MASTER
A DATA A P
0 b7:b0 0
S
2945 F06
A: ACKNOWLEDGE (LOW)
A: NOT ACKNOWLEDGE (HIGH)
R: READ BIT (HIGH)
ADDRESS W A
COMMAND
1 1 0 a3:a0 0 0
X X b5:b0
A DATA
COMMAND
X X b5:b0
A DATA A DATA A P
0 b7:b0 0 b7:b0 0
2945 F07
W: WRITE BIT (LOW)
S: START CONDITION
P: STOP CONDITION
Figure 6. LTC2945 Serial Bus SDA Write Byte Protocol
S
ADDRESS W A
1 1 0 a3:a0 0 0
Figure 7. LTC2945 Serial Bus SDA Write Word Protocol
A DATA A
...
DATA
0 b7:b0 0 b7:b0 0
...
b7:b0 0
A P
S
ADDRESS W A
COMMAND
1 1 0 a3:a0 0 0
X X b5:b0
A S
ADDRESS
0
1 1 0 a3:a0 1 0 b7:b0 1
R A DATA A P
2945 F08
2945 F09
Figure 8. LTC2945 Serial Bus SDA Write Page Protocol
S
ADDRESS W A
COMMAND
1 1 0 a3:a0 0 0
X X b5:b0
Figure 9. LTC2945 Serial Bus SDA Read Byte Protocol
A S
ADDRESS
0
1 1 0 a3:a0 1 0 b7:b0 0 b7:b0 1
R A DATA A DATA A P
2945 F10
Figure 10. LTC2945 Serial Bus SDA Read Word Protocol
S
ADDRESS W A
COMMAND
1 1 0 a3:a0 0 0
X X b5:b0
A S
ADDRESS
R A DATA A DATA
...
DATA A P
0
1 1 0 a3:a0 1 0 b7:b0 0 b7:b0
...
b7:b0 1
2945 F11
Figure 11. LTC2945 Serial Bus SDA Read Page Protocol
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LTC2945
APPLICATIONS INFORMATION
Stuck-Bus Reset
The LTC2945 I2C interface features a stuck bus reset timer
to prevent it from holding the bus lines low indefinitely if
the SCL signal is interrupted during a transfer. The timer
starts when either SCL or SDAI is low, and resets when
both SCL and SDAI are pulled high. If either SCL or SDAI
are low for over 33ms, the stuck-bus timer will expire and
the internal I2C interface and the SDAO pin pulldown logic
will be reset to release the bus. Normal communication
will resume at the next Start command.
Acknowledge
The acknowledge signal is used for handshaking between
the transmitter and the receiver to indicate that the last
byte of data was received. The transmitter always releases
the SDA line during the acknowledge clock pulse. The
LTC2945 will pull the SDA line low on the 9th clock cycle
to acknowledge receipt of the data. If the slave fails to
acknowledge by leaving SDA high, then the master can
abort the transmission by generating a Stop condition.
When the master is receiving data from the slave, the
master must acknowledge the slave by pulling down the
SDA line during the 9th clock pulse to indicate receipt of
a data byte. After the last byte has been received by the
master, it will leave the SDA line high (not acknowledge)
and issue a Stop condition to terminate the transmission.
Write Protocol
The master begins a write operation with a Start condition
followed by the seven-bit slave address and the R/W bit
set to zero. After the addressed LTC2945 acknowledges
the address byte, the master then sends a command byte
that indicates which internal register the master wishes to
write. The LTC2945 acknowledges this and then latches the
lower six bits of the command byte into its internal register
address pointer. The master then delivers the data byte and
the LTC2945 acknowledges once more and writes the data
into the internal register pointed to by the register address
pointer. If the master continues sending additional data
bytes with a Write Word or extended Write command, the
additional data bytes will be acknowledged by the LTC2945,
the register address pointer will automatically increment by
one, and data will be written as above. The write operation
terminates and the register address pointer resets to 00h
when the master sends a Stop condition.
Read Protocol
The master begins a read operation with a Start condition
followed by the 7-bit slave address and the R/W bit set
to zero. After the addressed LTC2945 acknowledges the
address byte, the master then sends a command byte
that indicates which internal register the master wishes to
read. The LTC2945 acknowledges this and then latches the
lower six bits of the command byte into its internal register
address pointer. The master then sends a repeated Start
condition followed by the same 7-bit address with the R/W
bit now set to 1. The LTC2945 acknowledges and sends
the contents of the requested register. The transmission
terminates when the master sends a Stop condition. If the
master acknowledges the transmitted data byte, as in a
Read Word command, the LTC2945 will send the contents
of the next register. If the master keeps acknowledging,
the LTC2945 will keep incrementing the register address
pointer and sending out data bytes. The read operation
terminates and the register address pointer resets to 00h
when the master sends a Stop condition.
Alert Response Protocol
When any of the fault bits in the FAULT register are set, a
bus alert is generated if the appropriate bit in the ALERT
register has been set. This allows the bus master to select
which faults will generate alerts. At power-up, the ALERT
register is cleared (no alerts enabled) and the ALERT pin is
high. If an alert is enabled, the corresponding fault causes
the ALERT pin to pull low. The bus master responds to the
alert in accordance with the SMBus alert response protocol
by broadcasting the Alert Response Address (0001100)b,
and the LTC2945 replies with its own address and releases
its ALERT pin as shown in Figure 12. The ALERT line is also
released if the FAULT or FAULT CoR registers are read (see
Table 2) since the faulting event can be identified by the
content in these registers. The ALERT signal is not pulled
low again until the Fault register indicates a different fault
has occurred or the original fault is cleared and it occurs
again. Note that this means repeated or continuing faults
will not generate additional alerts until the associated
FAULT register bits have been cleared.
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17
LTC2945
APPLICATIONS INFORMATION
If two or more LTC2945s on the same bus are generating
alerts when the ARA is broadcasted, the bus master will
repeat the alert response protocol until the ALERT line
is released. The device with the highest priority (lowest
address) will reply first and the device with the lowest
priority (highest address) will reply last.
ALERT
S RESPONSE R A
ADDRESS
0001100 1 0
DEVICE
ADDRESS
a7:a0
A P
1
2945 F12
Figure 12. LTC2945 Serial Bus SDA Alert Response Protocol
Opto-Isolating the I2C Bus
I2 C
device is complicated
Opto-isolating a standard
by the bidirectional SDA pin. The LTC2945/LTC2945-1
minimize this problem by splitting the standard I2C SDA
line into SDAI (input) and SDAO (output, LTC2945) or
SDAO (inverted output, LTC2945-1). The SCL is an input
only pin and does not require special circuitry to isolate.
For conventional non-isolated I2C applications, use the
LTC2945 and tie the SDAI and SDAO pins together to form
a standard I2C SDA pin.
Low speed isolated interfaces that use standard opendrain opto-isolators typically use the LTC2945 with the
SDAI and SDAO pins separated as shown in Figure 13.
Connect SDAI to the output of the incoming opto-isolator
with a pullup resistor to INTVCC or a local 5V supply; connect SDAO to the cathode of the outgoing opto-isolator
with a current-limiting resistor in series with the anode.
The input and output must be connected together on the
isolated side of the bus to allow the LTC2945 to participate
in I2C arbitration. Note that maximum I2C bus speed will
generally be limited by the speed of the opto-couplers
used in this application.
Both low and high side shunt regulators can supply up to
34mA of current to drive opto-isolator and pullup resistors as shown in Figure 14 and 15. For identical SDAI/SCL
pullup resistors the maximum load is:
1
2
ILOAD(MAX)= 6.7 +
R1 R3
(2)
RSHUNT can then be calculated using Equation 1. Note that
both LTC2945 and LTC2945-1 can be used in the shunt
regulator applications mentioned.
Figure 16 shows an alternate connection for use with lowspeed opto-couplers and the LTC2945-1. This circuit uses
a limited-current pullup on the internally clamped SDAI
pin and clamps the SDAO pin with the input diode of the
outgoing opto-isolator, removing the need to use INTVCC
for biasing in the absence of an auxiliary low voltage supply. For proper clamping:
VS(MAX ) – 5.9V
VS(MIN) – 6.9V
≤R4 ≤
(3)
5mA
0.5mA
As an example, a supply that operates from 36V to 72V
would require the value of R4 to be between 13k and 58k.
The LTC2945-1 must be used in this application to ensure
that the SDAO signal polarity is correct.
The LTC2945-1 can also be used with high-speed optocouplers with push-pull outputs and inverted logic as
shown in Figure 17. The incoming opto-isolator draws
power from the INTVCC, and the data output is connected
directly to the SDAI pin with no pullup required. Ensure
the current drawn does not exceed the 10mA maximum
capability of the INTVCC pin. The SDAO pin is connected
to the cathode of the outgoing optocoupler with a current
limiting resistor connected back to INTVCC. An additional
discrete N-channel MOSFET is required at the output of
the outgoing optocoupler to provide the open-drain pulldown that the I2C bus requires. Finally, the input of the
incoming opto-isolator is connected back to the output
as in the low-speed case.
Layout Considerations
A Kelvin connection between the sense resistor RSNS and
the LTC2945 is recommended to achieve accurate current
sensing (Figure 18). The recommended minimum trace
width for 1oz copper foil is 0.02” per amp to ensure the
trace stays at a reasonable temperature. Using 0.03” per
amp or wider is preferred. Note that 1oz copper exhibits
a sheet resistance of about 530μΩ per square.
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LTC2945
APPLICATIONS INFORMATION
3.3V
5V
R4
10k
SDAI
R5
0.82k
R6
0.51k
R7
10k
VDD
LTC2945
µP
1/2 MOCD207M
SDA
GND
GND
SDAO
1/2 MOCD207M
2945 F13
Figure 13. Opto-Isolation of a 10kHz I2C Interface Between LTC2945 and Microcontroller (SCL Omitted for Clarity)
GND
RSHUNT
3.3V
R3
1k
R1
10k
R2
0.51k
R4
10k
SDAI
INTVCC
VDD
VDD
LTC2945
VEE
C1
1µF
µP
1/2 MOCD207M
SDA
GND
GND
SENSE–
VEE
SDAO
SENSE+
1/2 MOCD207M
2945 F14
VOUT
RSNS
0.02Ω
Figure 14. Low Speed 10kHz Opto-Isolators Powered from Low-Side Shunt Regulator
RSNS
0.02Ω
VIN
SENSE+
3.3V
VOUT
SENSE–
R3
1k
R1
10k
R2
1k
R4
10k
SDAI
INTVCC
VDD
VDD
LTC2945-1
C1
1µF
µP
1/2 MOCD207M
SDA
SDAO
GND
GND
1/2 MOCD207M
2945 F15
RSHUNT
Figure 15. Low Speed 10kHz Opto-Isolators Powered from High-Side Shunt Regulator
For more information www.linear.com/LTC2945
2945fb
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LTC2945
APPLICATIONS INFORMATION
3.3V
48V
R4
20k
R5
7.5k
R6
0.51k
R7
10k
SDAI
VDD
LTC2945-1
µP
1/2 MOCD207M
SDAO
GND
SDA
GND
1/2 MOCD207M
2945 F16
Figure 16. Opto-Isolation of a 1.5kHz I2C Interface Between LTC2945-1 and Microcontroller (SCL Omitted for Clarity)
VIN
48V
C1
1µF
INTVCC
VDD
C2
1µF
1/2 ACPL-064L*
R5
2k
3.3V
VCC
LTC2945-1
M1
GND
SDAO
R6
2k
BS170
R7
2k
VDD
VCC
µP
ISO_SDA
SDAI
GND
GND
SDA
GND
2945 F17
1/2 ACPL-064L*
* CMOS OUTPUT
Figure 17. Opto-Isolation of I2C Interface with Low Power, High Speed Opto-couplers (SCL Omitted for Clarity)
RSNS
TO
LOAD
12
2
11
3
10
4
9
5
8
6
7
SENSE –
1
SENSE+
VIN
2945 F18
Figure 18. Recommended Layout for Kelvin Connection
2945fb
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LTC2945
APPLICATIONS INFORMATION
Table 1. LTC2945 Device Addressing
HEX
DEVICE
ADDRESS
DESCRIPTION
h
LTC2945
ADDRESS
PINS
BINARY DEVICE ADDRESS
a6
a5
a4
a3
a2
a1
a0
R/W
ADR1
ADR0
Mass Write
CC
1
1
0
0
1
1
0
0
X
X
Alert Response
19
0
0
0
1
1
0
0
1
X
X
0
CE
1
1
0
0
1
1
1
X
H
L
1
D0
1
1
0
1
0
0
0
X
NC
H
2
D2
1
1
0
1
0
0
1
X
H
H
3
D4
1
1
0
1
0
1
0
X
NC
NC
4
D6
1
1
0
1
0
1
1
X
NC
L
5
D8
1
1
0
1
1
0
0
X
L
H
6
DA
1
1
0
1
1
0
1
X
H
NC
7
DC
1
1
0
1
1
1
0
X
L
NC
8
DE
1
1
0
1
1
1
1
X
L
L
Table 2. LTC2945 Register Addresses and Contents
REGISTER
ADDRESS
REGISTER NAME
READ/WRITE
00h
CONTROL (A)
R/W
01h
ALERT (B)
R/W
02h
STATUS (C)
R
DESCRIPTION
Controls ADC Operation Mode and Test Mode
DEFAULT
05h
Selects Which Faults Generate Alerts
00h
System Status Information
00h
03h
FAULT (D)
R/W
Fault Log
00h
04h
FAULT CoR (E)
CoR
Same Data as Register D, D Content Cleared on Read
00h
05h
POWER MSB2
R/W**
Power MSB2 Data
XXh
06h
POWER MSB1
R/W**
Power MSB1 Data
XXh
07h
POWER LSB
R/W**
Power LSB Data
XXh
08h
MAX POWER MSB2
R/W**
Maximum Power MSB2 Data
00h
09h
MAX POWER MSB1
R/W**
Maximum Power MSB1 Data
00h
0Ah
MAX POWER LSB
R/W**
Maximum Power LSB Data
00h
0Bh
MIN POWER MSB2
R/W**
Minimum Power MSB2 Data
FFh
0Ch
MIN POWER MSB1
R/W**
Minimum Power MSB1 Data
FFh
0Dh
MIN POWER LSB
R/W**
Minimum Power LSB Data
FFh
0Eh
MAX POWER THRESHOLD MSB2
R/W
Maximum Power Threshold MSB2 to Generate Alert
FFh
0Fh
MAX POWER THRESHOLD MSB1
R/W
Maximum Power Threshold MSB1 to Generate Alert
FFh
10h
MAX POWER THRESHOLD LSB
R/W
Maximum Power Threshold LSB to Generate Alert
FFh
11h
MIN POWER THRESHOLD MSB2
R/W
Minimum Power Threshold MSB2 to Generate Alert
00h
12h
MIN POWER THRESHOLD MSB1
R/W
Minimum Power Threshold MSB1 to Generate Alert
00h
13h
MIN POWER THRESHOLD LSB
R/W
Minimum Power Threshold LSB to Generate Alert
00h
14h
∆SENSE MSB
R/W**
∆SENSE MSB Data
XXh
15h
∆SENSE LSB
R/W**
∆SENSE LSB Data
X0h
16h
MAX ∆SENSE MSB
R/W**
Maximum ∆SENSE MSB Data
00h
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21
LTC2945
APPLICATIONS INFORMATION
17h
MAX ∆SENSE LSB
R/W**
Maximum ∆SENSE LSB Data
00h
18h
MIN ∆SENSE MSB
R/W**
Minimum ∆SENSE MSB Data
FFh
19h
MIN ∆SENSE LSB
R/W**
Minimum ∆SENSE LSB Data
FOh
1Ah
MAX ∆SENSE THRESHOLD MSB
R/W
Maximum ∆SENSE Threshold MSB to Generate Alert
FFh
1Bh
MAX ∆SENSE THRESHOLD LSB
R/W
Maximum ∆SENSE Threshold LSB to Generate Alert
FOh
1Ch
MIN ∆SENSE THRESHOLD MSB
R/W
Minimum ∆SENSE Threshold MSB to Generate Alert
00h
1Dh
MIN ∆SENSE THRESHOLD LSB
R/W
Minimum ∆SENSE Threshold LSB to Generate Alert
00h
1Eh
VIN MSB
R/W**
ADC VIN MSB Data
XXh
1Fh
VIN LSB
R/W**
ADC VIN LSB Data
X0h
20h
MAX VIN MSB
R/W**
Maximum VIN MSB Data
00h
21h
MAX VIN LSB
R/W**
Maximum VIN LSB Data
00h
22h
MIN VIN MSB
R/W**
Minimum VIN MSB Data
FFh
23h
MIN VIN LSB
R/W**
Minimum VIN LSB Data
FOh
24h
MAX VIN THRESHOLD MSB
R/W
Maximum VIN Threshold MSB to Generate Alert
FFh
25h
MAX VIN THRESHOLD LSB
R/W
Maximum VIN Threshold LSB to Generate Alert
FOh
26h
MIN VIN THRESHOLD MSB
R/W
Minimum VIN Threshold MSB to Generate Alert
00h
27h
MIN VIN THRESHOLD LSB
R/W
Minimum VIN Threshold LSB to Generate Alert
00h
28h
ADIN MSB
R/W**
ADIN MSB Data
XXh
29h
ADIN LSB
R/W**
ADIN LSB Data
X0h
2Ah
MAX ADIN MSB
R/W**
Maximum ADIN MSB Data
00h
2Bh
MAX ADIN LSB
R/W**
Maximum ADIN LSB Data
00h
2Ch
MIN ADIN MSB
R/W**
Minimum ADIN MSB Data
FFh
2Dh
MIN ADIN LSB
R/W**
Minimum ADIN LSB Data
FOh
2Eh
MAX ADIN THRESHOLD MSB
R/W
Maximum ADIN Threshold MSB to Generate Alert
FFh
2Fh
MAX ADIN THRESHOLD LSB
R/W
Maximum ADIN Threshold LSB to Generate Alert
FOh
30h
MIN ADIN THRESHOLD MSB
R/W
Minimum ADIN Threshold MSB to Generate Alert
00h
31h
MIN ADIN THRESHOLD LSB
R/W
Minimum ADIN Threshold LSB to Generate Alert
00h
*Register address MSBs b7-b6 are ignored. ** Writable if bit A4 is set
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LTC2945
APPLICATIONS INFORMATION
Table 3. CONTROL Register A (00h) - Read/Write
BIT
NAME
OPERATION
A7
ADC Snapshot Mode Enable
Enables ADC Snapshot Mode; 1 = Snapshot Mode Enabled. Only channel selected by A6 and A5 is
measured by the ADC. After the conversion, the BUSY bit is reset and the ADC is halted.
0 = Snapshot Mode Disabled (Continuous Scan Mode. Default)
A6
ADC Channel Label for Snapshot Mode ADC Channel Label for Snapshot Mode
A5
A6
A5
ADC Channel
0
0
∆SENSE (Default)
0
1
VIN
1
0
ADIN
A4
Test Mode Enable
Test Mode Halts ADC Operation and Enables Writes to Internal ADC/LOGIC Registers;
1 = Enable Test Mode, 0 = Disable Test Mode (Default)
A3
ADC Busy in Snapshot Mode
ADC Current Status; 1 = ADC Converting, 0 = ADC Conversion Completed (Default), Not Writable
A2
VIN Monitor
Enables VDD or SENSE+ Voltage Monitoring; 1 = Monitor SENSE+ Voltage (Default),
0 = Monitor VDD Voltage
A1
Shutdown Enable
Enables Low-IQ / Shutdown Mode; 1 = Enable Shutdown, 0 = Normal Operation (Default)
A0
Multiplier Select
Selects ADIN or SENSE+/VDD (depends on A2) data for digital multiplication with SENSE data;
1 = Select SENSE+/VDD (Default), 0 = Select ADIN
Table 4. ALERT Register B (01h) - Read/Write
BIT
B7
NAME
Maximum POWER Alert
B6
Minimum POWER Alert
B5
Maximum ∆SENSE Alert
B4
Minimum ∆SENSE Alert
B3
Maximum VIN Alert
B2
Minimum VIN Alert
B1
Maximum ADIN Alert
B0
Minimum ADIN Alert
OPERATION
Enables Alert When POWER Calculation Data is > Maximum Power Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When POWER Calculation Data is < Minimum Power Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC ∆SENSE Measurement Data is > Maximum ∆SENSE Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC ∆SENSE Measurement Data is < Minimum ∆SENSE Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC VIN Measurement Data is > Maximum VIN Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC VIN Measurement Data is < Minimum VIN Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC ADIN Measurement Data is > Maximum ADIN Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
Enables Alert When ADC ADIN Measurement Data is < Minimum ADIN Threshold;
1 = Enable Alert,
0 = Disable Alert (Default)
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23
LTC2945
APPLICATIONS INFORMATION
Table 5. STATUS Register C (02h) - Read
BIT
C7
NAME
POWER Overvalue Present
C6
POWER Undervalue Present
C5
∆SENSE Overvalue Present
C4
∆SENSE Undervalue Present
C3
VIN Overvalue Present
C2
VIN Undervalue Present
C1
ADIN Overvalue Present
C0
ADIN Undervalue Present
OPERATION
Indicates POWER Overvalue When POWER is > Maximum Power Threshold;
1 = POWER Overvalue,
0 = POWER Not Overvalue
Indicates POWER Undervalue When POWER is < Minimum Power Threshold;
1 = POWER Undervalue,
0 = POWER Not Undervalue
Indicates ∆SENSE Overvalue When ∆SENSE is > Maximum ∆SENSE Threshold;
1 = ∆SENSE Overvalue,
0 = ∆SENSE Not Overvalue
Indicates ∆SENSE Undervalue When ∆SENSE is < Minimum ∆SENSE Threshold;
1 = ∆SENSE Undervalue,
0 = ∆SENSE Not Undervalue
Indicates VIN Overvalue When VIN is > Maximum VIN Threshold;
1 = VIN Overvalue,
0 = VIN Not Overvalue
Indicates VIN Undervalue When VIN is < Minimum VIN Threshold;
1 = VIN Undervalue,
0 = VIN Not Undervalue
Indicates ADIN Overvalue When ADIN is > Maximum ADIN Threshold;
1 = ADIN Overvalue,
0 = ADIN Not Overvalue
Indicates ADIN Undervalue When ADIN is < Minimum ADIN Threshold;
1 = ADIN Undervalue,
0 = ADIN Not Undervalue
Table 6. FAULT Register D (03h) - Read/Write
BIT
D7
NAME
POWER Overvalue Fault
Occurred
D6
POWER Undervalue Fault
Occurred
D5
∆SENSE Overvalue Fault
Occurred
D4
∆SENSE Undervalue Fault
Occurred
D3
VIN Overvalue Fault
Occurred
D2
VIN Undervalue Fault
Occurred
D1
ADIN Overvalue Fault
Occurred
D0
ADIN Undervalue Fault
Occurred
OPERATION
Indicates POWER Overvalue Fault When POWER was > Maximum Power Threshold;
1 = POWER Overvalue Fault Occurred,
0 = No POWER Overvalue Faults
Indicates POWER Undervalue Fault When POWER was < Minimum Power Threshold;
1 = POWER Undervalue Fault Occurred,
0 = No POWER Undervalue Faults
Indicates ∆SENSE Overvalue Fault When ΔSENSE was > Maximum ∆SENSE Threshold;
1 = ∆SENSE Overvalue Fault Occurred,
0 = No ∆SENSE Overvalue Faults
Indicates ∆SENSE Undervalue Fault When ∆SENSE was < Minimum ∆SENSE Threshold;
1 = ∆SENSE Undervalue Fault Occurred,
0 = No ∆SENSE Undervalue Faults
Indicates VIN Overvalue Fault When VIN was > Maximum VIN Threshold;
1 = VIN Overvalue Fault Occurred,
0 = No VIN Overvalue Faults
Indicates VIN Undervalue Fault When VIN was < Minimum VIN Threshold;
1 = VIN Undervalue Fault Occurred,
0 = No VIN Undervalue Faults
Indicates ADIN Overvalue Fault When ADIN was > Maximum ADIN Threshold;
1 = ADIN Overvalue Fault Occurred,
0 = No ADIN Overvalue Faults
Indicates ADIN Undervalue Fault When ADIN was < Minimum ADIN Threshold;
1 = ADIN Undervalue Fault Occurred,
0 = No ADIN Undervalue Faults
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LTC2945
APPLICATIONS INFORMATION
Table 7. ADC, ADC MIN/MAX, MIN/MAX ADC THRESHOLD Register Data Format: MSB Bytes-Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (11)
Data (10)
Data (9)
Data (8)
Data (7)
Data (6)
Data (5)
Data (4)
*Set Bit A4 before writing to ADC and MIN/MAX ADC Registers
Table 8. ADC, ADC MIN/MAX, MIN/MAX THRESHOLD Register Data Format: LSB Bytes-Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (3)
Data (2)
Data (1)
Data (0)
Reserved**
Reserved**
Reserved**
Reserved**
* Set Bit A4 before writing to ADC and MIN/MAX ADC Registers
** Read as ‘0’
Table 9. POWER, MIN/MAX POWER, MIN/MAX POWER THRESHOLD Register Data Format: MSB2 Bytes- Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (23)
Data (22)
Data (21)
Data (20)
Data (19)
Data (18)
Data (17)
Data (16)
* Set Bit A4 before writing to POWER and MIN/MAX POWER Registers
Table 10. POWER, MIN/MAX POWER, MIN/MAX POWER THRESHOLD Register Data Format: MSB1 Bytes- Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (15)
Data (14)
Data (13)
Data (12)
Data (11)
Data (10)
Data (9)
Data (8)
* Set Bit A4 before writing to POWER and MIN/MAX POWER Registers
Table 11. POWER, MIN/MAX POWER, MIN/MAX POWER THRESHOLD Register Data Format: LSB Bytes- Read/Write*
BIT (7)
BIT (6)
BIT (5)
BIT (4)
BIT (3)
BIT (2)
BIT (1)
BIT (0)
Data (7)
Data (6)
Data (5)
Data (4)
Data (3)
Data (2)
Data (1)
Data (0)
* Set Bit A4 before writing to POWER and MIN/MAX POWER Registers
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25
LTC2945
TYPICAL APPLICATIONS
A Wide Range Supply Monitor
RSNS
0.02Ω
VIN
0V TO 80V
SENSE+
2.7V TO 5.9V
VOUT
SENSE–
R1
2k
R2
2k
R3
2k
SCL
INTVCC
SDA
ADR1
SDAO
INT
VADIN
ADIN
GND
3.3V
VOUT
SENSE–
R1
2k
R2
2k
R3
2k
VDD
SCL
SCL
INTVCC
SDAI
SDA
ADR1
SDAO
VDD
µP
C2
0.1µF
ALERT
ADR0
SENSE+
VDD
SCL
LTC2945
RSNS
0.02Ω
VIN
4V TO 80V
3.3V
SDAI
VDD
C2
0.1µF
Wide Range Supply Monitor with Wide Range VDD Input
LTC2945
GND
INT
ALERT
ADR0
GND
µP
VADIN
ADIN
GND
2945 TA02
2945 TA03
Dual Supply Monitor with Common Opto-coupler for Galvanic Isolation
3.3V
R8
0.51k
RSNS1
0.02Ω
VIN1
24V
SENSE+
C1
1µF
VCC1
VDD
SENSE–
SCL
ADR1
SDAO
ALERT
ADIN
GND
RSNS2
0.02Ω
C4
0.1µF
µP
VCC2
VADIN1
R6
1k
VCC2
HCPL063L
SDAI
SENSE+
VDD
R12
10k
VDD
ADR0
VIN2
48V
R11
10k
VCC
LTC2945
GND
C3
1µF
R5
V
10k CC1
R10
10k
SCL
INTVCC
C2
0.1µF
VOUT1
R4
10k
R9
0.51k
R7
1k
3.3V
VCC
SDA
VOUT2
SENSE–
SCL
INT
GND
LTC2945
INTVCC
GND
HCPL063L
SDAI
SDAO
ALERT
ADR1
ADR0
GND
ADIN
VADIN2
2945 TA04
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LTC2945
TYPICAL APPLICATIONS
Power Monitoring in –48V System Using Low Side Sensing (1.5kHz I2C Interface)
–48V
RTN
R1
20k
R2
20k
3.3V
C2
0.1µF
VDD INTVCC ADR1
C1
1µF
R4
1k
R7
0.51k
R3
1k
R8
0.51k
R9
10k
R10
10k
R11
10k
VDD
SCL
LTC2945
SCL
SDAI
µP
VEE
MOCD207M
GND
SDA
ADIN
SDAO
ADR0
INT
GND
ALERT
SENSE –
VEE
–48V INPUT
SENSE+
MOCD207M
CONTROL REGISTER A2 = 0
VOUT
RSNS
0.02Ω
2945 TA05
Power Monitoring in –48V Harsh Environment Using INTVCC Shunt Regulator to Tolerate 200V Transients
–48V
RTN
RSHUNT
3 × 1.8k IN SERIES
R12
100
Q1
PZTA42
D1
1N4148WS
C2
1µF
VDD
R4
1k
INTVCC
ADR1
R5
735k
R1
1k
R2
1k
VEE
R7
0.51k
R8
0.51k
R9
1k
R10
1k
R11
10k
VDD
VCC
LTC2945
C1
1µF
R3
0.51k
3.3V
SCL
SCL
SDAI
ADIN
SDA
GND
R6
15k
HCPL-063L V
EE
µP
3.3V
VCC
GND
ADR0
SDAO
INT
ALERT
SENSE –
VEE
–48V INPUT
GND
SENSE+
GND
2945 TA06
HCPL-063L
CONTROL REGISTER A0 = 0
RSNS
0.02Ω
VOUT
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LTC2945
TYPICAL APPLICATIONS
Power Monitoring in –48V System Using External Linear Regulator to Supply Opto-couplers and SCL/SDA Resistive Pull-Ups
LT3010-5
–48V
RTN
IN
C3
0.1µF
OUT
C2
1µF
SHDN SENSE
GND
5V
VEE
R7
0.5k
VDD
R4
1k
ADR1
INTVCC
R1
1k
R2
10k
R8
0.51k
R9
1k
R10
1k
R11
10k
VDD
VCC
SCL
LTC2945
C1
1µF
R3
0.51k
SCL
SDAI
SDA
GND
PS9817-2
GND
µP
5V
VEE
VCC
ADIN
SDAO
ADR0
INT
ALERT
SENSE –
GND
SENSE+
GND
2945 TA07
PS9817-2
CONTROL REGISTER A2 = 0
VEE
–48V INPUT
VOUT
RSNS
0.02Ω
Wide Range Dual Supply Monitor with Single LTC2945
D1
BAT54
RSNS1
0.02Ω
SUPPLY B
4.5V TO 80V
RIN1
1k
SUPPLY A
4.5V TO 80V
–INF –INS
C1
0.1µF
RSNS
0.02Ω
RIN2
1k
D2
BAT54
+IN
C3
0.1µF
RSHUNT*
V+
LTC6102
OUT
RADIN
20k
V–
SENSE–
LTC2945
SCL
INTVCC
ADR1
C2
0.1µF
VREG
SENSE+
VDD
TO
LOAD
ADIN
ADR0
SDAI
GND
I2C
INTERFACE
SDAO
ALERT
2945 TA08
CONTROL REG
A2
VOLTAGE
DATA
CURRENT POWER
DATA
DATA
SUPPLY A
1
SENSE+
∆SENSE INTERNALLY GENERATED
SUPPLY B
0
VDD**
ADIN
USE EXTERNAL µP TO MULTIPLY VOLTAGE (VDD)
AND CURRENT (ADIN) DATA
* SELECT RSHUNT ACCORDING TO THE EQUATION IN THE “FLEXIBLE POWER SUPPLY TO LTC2945” SECTION.
** VOLTAGE DATA HAS AN OFFSET VALUE DUE TO D1’S DROP, IF DESIRABLE THIS CAN BE COMPENSATED THROUGH SOFTWARE.
2945fb
28
For more information www.linear.com/LTC2945
LTC2945
TYPICAL APPLICATIONS
Ruggedized 4V to 70V High Side Power Monitor with Surge Protection Up to 200V
RSNS
0.02Ω
VIN
SENSE +
VOUT
SENSE–
INTVCC
VDD
R12
100Ω
R4
1k
LTC2945
T1
SMAJ70A
DIODES, INC
Q1
PZTA42
R1
1k
R3
0.51k
3.3V
C2
1µF
R2
1k
R8
0.51k
R7
0.51k
FGND
R9
1k
R10
1k
R11
10k
VDD
VCC
SCL
C1
0.1µF
SCL
SDAI
SDA
GND
HCPL-063L
FGND
µP
3.3V
VCC
ADR1
ADR0
SDAO
ADIN
INT
ALERT
GND
GND
GND
2945 TA09
HCPL-063L
FGND
M1
BSP149
R5
1Ω
Isolated Wide Range I2C Power Monitor
LTM2883-3I
3.3V
ON
GND
V+
AV+
V–
AV–
VCC2
AVCC2
DI1
SDA
SCL
DNC
DO2
DO1
GND
O1
SDA2
SCL2
DNC
I2
I1
GND2
VCC
VL
1µF
10k
VCC
µP
SDA
SCL
INT
GND
10k
RSNS
0.02Ω
VIN
0V TO 80V
SENSE+
VOUT
SENSE–
LTC2945
R2
10k
C2
0.1µF
VDD
INTVCC
SDAO
SDAI
SCL
ALERT
ADIN
VADIN
ADR1
ADR0
GND
2945 TA09a
2945fb
For more information www.linear.com/LTC2945
29
LTC2945
TYPICAL APPLICATIONS
Wide Range –4V to –500V Negative Power Monitor (10kHz I2C Interface)
RTN
M1
BSP135
R5
750k
R13
10k
R4
1k
R3
1k
R1
2k
R2
2k
VDD
R6
750k
3.3V
C1
0.1µF
VEE
R7
0.51k
R8
0.51k
R9
10k
R10
10k
R11
10k
VDD
SCL
Z1
4.7V
LTC2945
SCL
SDAI
VEE
ADIN
GND
R12
5k
SDA
ADR1
SDAO
INT
ADR0
C2
0.1µF
µP
MOCD207M
SENSE –
+
SENSE
CONTROL REGISTER A2 = 0
VEE
RSNS
0.02Ω
GND
2945 TA10
ALERT
INTVCC
MOCD207M
VOUT
2945fb
30
For more information www.linear.com/LTC2945
LTC2945
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MS Package
12-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1668 Rev A)
0.889 ±0.127
(.035 ±.005)
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
0.65
(.0256)
BSC
0.42 ±0.038
(.0165 ±.0015)
TYP
12 11 10 9 8 7
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
DETAIL “A”
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
0° – 6° TYP
0.406 ±0.076
(.016 ±.003)
REF
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
0.18
(.007)
SEATING
PLANE
1 2 3 4 5 6
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
0.650
(.0256)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MS12) 0213 REV A
2945fb
For more information www.linear.com/LTC2945
31
LTC2945
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UD Package
12-Lead Plastic QFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1855 Rev Ø)
0.70 ±0.05
3.50 ±0.05
1.65 ±0.05
2.10 ±0.05 (4 SIDES)
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ± 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
PIN 1 NOTCH R = 0.20 TYP
OR 0.25 × 45° CHAMFER
R = 0.115
TYP
0.75 ±0.05
11
12
PIN 1
TOP MARK
(NOTE 6)
0.40 ±0.10
1
2
1.65 ±0.10
(4-SIDES)
(UD12) QFN 0709 REV Ø
0.200 REF
0.00 – 0.05
NOTE:
1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
0.25 ±0.05
0.50 BSC
2945fb
32
For more information www.linear.com/LTC2945
LTC2945
REVISION HISTORY
REV
DATE
DESCRIPTION
A
09/13
Added Limits to Full-Scale Voltage
4
Removed Note 5 from I2C Interface Timing
5
B
9/15
PAGE NUMBER
Added Note 5 to SCL, SDAI Input Capacitance
5
Added ADIN and Resistive Divider Information with Regards to Figure 3a and Figure 3c
12
Revised Figure 3a and Figure 3c
13
Revised Figure 13 and Figure 17
19, 20
Revised Bottom Figure
26
Top Figure: Replaced SMAJ78A with SMAJ70A and Changed C2 Connection from VEE to FGND
29
Added “Isolated Wide Range I2C Power Monitor” Figure
29
Added H-grade
2, 3
2945fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LTC2945
33
LTC2945
TYPICAL APPLICATION
3.3V Input Supply Monitor with 12V VDD Input
RSNS
0.02Ω
VIN
3.3V
SENSE+
VDD
12V
ADR1
C2
0.1µF
R1
2k
R2
2k
R3
2k
IN–
VDD
SCL
SDAI
SDA
RIN1
1k
GND
ADIN
SENSE+
INT
VADIN
IN+
VDD
GND
2945 TA12
2.7V TO 5.9V
INTVCC
RIN2
1k
RSNS
0.02Ω
VIN
0V TO 44V
µP
SDAO
ALERT
ADR0
VOUT
V–
SCL
LTC2945
INTVCC
LT6105
V+
3.3V
VOUT
SENSE–
Rail-to-Rail Bidirectional Current and Power Monitor
TO
LOAD
SENSE–
LTC2945
SCL
I2C
INTERFACE
SDAI
SDAO
ADR1
ALERT
ADR0
ADIN
RADIN
20k
GND
2945 TA11
CONTROL REG
A2
VOLTAGE
DATA
CURRENT
DATA
POWER
DATA
FORWARD
1
SENSE+
∆SENSE
INTERNALLY GENERATED
REVERSE
1
SENSE+
ADIN
USE EXTERNAL µP TO
MULTIPLY VOLTAGE (SENSE+)
AND CURRENT (ADIN) DATA
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC4151
High Voltage I2C Current and Voltage Monitor
7V to 80V Operation, 12-Bit Resolution with ±1.25% TUE
LT6105
Rail-to-Rail Input Current Sense Amplifier
Very Wide Input Common Mode Range, 2.85V to 36V Operation
LTC2450
Easy-to-Use, Ultra-Tiny 16-Bit ADC
GND to VCC Single-Ended Input Range, 0.02 LSB RMS Noise, 2 LSB INL
(No Missing Codes), 2 LSB Offset Error, 4 LSB Full-Scale Error
LTC4215
Single Channel, Hot Swap Controller with I2C Monitoring
8-Bit ADC, Adjustable Current Limit and Inrush, 2.9V to 15V Operation
LTC4222
Dual Channel, Hot Swap Controller with I2C Monitoring
10-Bit ADC, Adjustable Current Limit and Inrush, 2.9V to 29V Operation
8-Bit ADC, Adjustable Current Limit and Inrush, 8.5V to 80V Operation
LTC4260
Positive High Voltage Hot Swap Controller with I2C Monitoring
LTC4261
Negative High Voltage Hot Swap Controller with I2C Monitoring 10-Bit ADC, Floating Topology, Adjustable Inrush
LTC2940
Power and Current Monitor
Four-Quadrant Multiplication, ±5% Power Accuracy, 4V to 80V Operation
LTC2970
Dual I2C Power Supply Monitor and Margining Controller
14-Bit ADC with ±0.5% TUE, Dual 8-Bit DACs
LTC2974
Quad Digital Power Supply Manager with EEPROM
16-Bit ADC with ±0.25% TUE, Supervise/Sequence/Monitor/Margin/
Trim, Configuration/Fault Logging EEPROM, I2C, Supervise/Monitor
Current and Temperature
LTC2978
Octal Digital Power Supply Manager with EEPROM
16-Bit ADC with ±0.25% TUE, Supervise/Sequence/Monitor/Margin/
Trim, Configuration/Fault Logging EEPROM, I2C
2945fb
34 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC2945
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC2945
LT 0915 REV B • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2012
工商网监
湘ICP备2023018690号
