Datasheet
Genesys 2 FPGA Board Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 6 of 31
3 Power monitoring
I
2
C-interfaced monitoring circuits, INA219 from Texas Instruments, are available on the main power rails. These allow real-time voltage, current,
and power readings in the FPGA. Six such circuits share the same I
2
C bus with different slave addresses. These are summarized in
Table 3, along with recommended configuration values.
Supply
rail
I
2
C device
address
Shunt
resistor
Configuration
register
Calibration
register
Designator
VCC1V0
b1000101
5 mΩ
0x0867
0x4000
IC29
VCC1V5
b1001100
IC33
VCC1V8
b1001000
IC35
VADJ
b1000001
IC34
VCC3V3
b1000100
IC44
VCC5V0
b1000000
IC46
Table 3. Power monitoring circuit parameters.
The configuration and calibration registers are volatile, so they need to be initialized after power-up. After
initialization is done voltage, current, and power values can be read from dedicated registers. It is recommended
to add glitch filters to the I
2
C master controller to avoid spurious start or stop conditions occurring on the bus. This
is especially important when using an external I
2
C master connected to the J18 header (not mounted by default).
For more information on the INA219, see its datasheet
4
.
The principle of operation is measuring bus and shunt voltages using a programmable-gain differential amplifier
and an analog-to-digital converter. The schematic for one such circuit is shown in Figure 3. The two analog inputs
are connected across a shunt resistor placed in series between the power supply and the load. Current consumed
by the load produce a voltage drop across the shunt resistor. This voltage is measured by the INA219 and is used to
calculate the current. In addition, the bus voltage is measured on V- with respect to GND and is the voltage on the
respective power rail. The voltage and current measurements are used to calculate power consumption. If the
INA219 is configured, it will correctly calculate all three parameters. In its default, power-up configuration it
provides bus and shunt voltage only, which can be used to calculate current and power in the FPGA.
INA219
V+ V-
Power supply
OUT
Power rail
SDA
Kintex-7
AF30
SCL
AE30
VCC3V3
Figure 3. Power monitoring circuit
4
http://www.ti.com/lit/gpn/ina219