DEMO MANUAL DC1697A
LTC2945
Wide Range I
2
C Power Monitor
DESCRIPTION
Demonstration circuit 1697A features the
LTC2945.
The
LTC2945 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 sup-
ply. The current common mode 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 I
2
C interface. The
demo board is populated for a 5A application. This can
be changed by populating R1 accordingly.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1697A
L,
LT, LTC, LTM, QuikEval, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
BOARD PHOTO
TO DC590
4V TO 80V
LOAD
dc1697A F01
Figure 1. Proper Test Equipment Setup
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DEMO MANUAL DC1697A
QUICK START PROCEDURE
Jumper Settings
VDD_SEL:
Selects the V
DD
source. It can be set to VIN,
INTVCC or EXTVDD (which requires a voltage to be present
at the EXTVDD turret.) Please see Hardware Setup sec-
tion for examples of how these different jumper settings
are used.
SDA:
Connects or separates the SDAI to SDAO pins. For use
with QuikEval
™
, leave it on TIE. The pins can be separated
in order to test applications using optoisolation.
ADR0, ADR1:
Selects the I
2
C slave address of the LTC2945.
Any changes here should also be made inside of QuikEval
for communications to persist.
External Connections
Signal connections are made via the row of turret posts
along the edges of the board.
GND:
(4 turrets)These turrets are connected directly to
the ground planes.
VIN:
Used as a supply and current sense input for the
internal current sense amplifier. Depending on the
configuration of VDD_SEL, can also be tied to EXTVDD.
EXTVDD:
High Voltage Supply Input. This pin powers an
internal series regulator with input voltages ranging from
5V to 80V and produces 5V for INTVCC when above 7V.
INTVCC:
Internal Low Voltage Supply Input/Output. This
turret is used to power internal circuitry and can be con-
figured as a direct input, as a linear regulator from a higher
voltage connected to V
DD
or as a shunt regulator. Please
see LTC2945 data sheet for more details.
ADIN:
ADC input measured by the onboard ADC. Can
measure between 0V and 2.048V.
VPU:
Pull up voltage for the
ALERT
LED. Connected on this
board to a 5V isolated supply on the DC590. If a DC590
is not used and the DC1697A is operated independently,
a 5V supply should be provided here.
Digital Connections
SCL:
I
2
C Clock turret
SDA/SDAI:
I
2
C Bus Data input, can be tied to SDAO through
the SDA Jumper.
SDAO:
I
2
C Bus Data output. Should be connected to SDAI.
ALERT:
Fault Alert Output. Connected to
ALERT
LED. Open
Drain logic output that is pulled to ground after an event
resulting in a fault occurs.
LEDs
ALERT:
Will light up red on an ALERT condition. Can also
be monitored on the
ALERT
turret.
INTVCC:
Will light up green when INTVCC is providing
power.
Operating Principles
The DC1697A was designed to be connected to the DC590
and controlled through the QuikEval suite of software. All
thresholds can be set and ADC registers read back through
the QuikEval interface, which was designed to provide a
convenient way to evaluate the LTC2945.
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DEMO MANUAL DC1697A
HARDWARE SETUP
Due to having separate V
DD
and SENSE pins, the LTC2945
offers great flexibility in terms of supply options. The fol-
lowing are some examples of how to connect and set up the
DC1697A based on different supply input configurations.
In order for the DC1697A to function, power must be
applied. If the VDD_SEL jumper is set to VIN, then V
DD
and
V
IN
are connected as shown in Figure 2. At this point, as
long as 4V to 80V is provided at VIN the part will function
correctly. However, should VDD_SEL be tied to EXTVDD
then a separate voltage source should be provided at the
EXTVDD turret. Should VDD_SEL be tied to INTVCC then,
if VIN is less than 7V, a 5V supply should be provided at
the INTVCC turret.
If the system is connected properly, the INTVCC green
LED should be lit and the
ALERT
red LED should be off.
Jumper VDD_SEL Set to VIN to Tie V
DD
to VIN
4V TO 80V
LOAD
dc1697A F02
Figure 2. DC1697A Is Powered from Supply Being Monitored
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DEMO MANUAL DC1697A
HARDWARE SETUP
INTVCC can also be used as a 6.3V shunt regulator. For
supplies greater than 80V, simply connect power through
a shunt resister for high or low shunt configuration as
shown in Figure 3 and 4 respectively. For this configuration,
ensure VDD_SEL is set to INTVCC.
The 5k shunt resistor shown provides 15mA to INTVCC at
80V. The allowable range of resistance for a given input
range is given by the following formula:
V
S(MAX)
– 5.9V
V
S(MIN)
– 6.7V
≤
R
SHNT
≤
35mA
1mA
+I
LOAD(MAX)
The DC590 provides isolation and level shifting, as the
I
2
C interface is operating at 5.9V to 6.7V below the supply
being monitored.
Jumper VDD_SEL Set to INTVCC With A Resistor Connected from DC1697 GND to Circuit Ground
> 80V
dc1697A F03
5k
Figure 3. Powering DC1697A Using High-Side Shunt Regulator to Allow for Input Voltage Higher Than 80V
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DEMO MANUAL DC1697A
HARDWARE SETUP
Jumper VDD_SEL Set to INTVCC with a Resistor Connected to INTVCC
0V TO 80V
LOAD
> 80V
5k
dc1697A F04
Figure 4. Powering DC1697A Through Low-Side Shunt Regulator in High-Side Current Sense Topology
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