Datasheet

Supply
Load
R 10W
FILTER
R 10W
FILTER
0.1 Fto1 Fm m
CeramicCapacitor
Current
Shunt
Data(SDA)
3.3VSupply
Clock(SCL)
´
PowerRegister
CurrentRegister
I C
Interface
2
VoltageRegister
V
IN+
V
IN-
ADC
PGA
INA219
GND
A0
A1
SupplyVoltage
V
S
INA219
www.ti.com SBOS448F –AUGUST 2008– REVISED SEPTEMBER 2011
Compatibility with TI Hot Swap Controllers
Although the INA219 can be read at any time, and
the data from the last conversion remain available,
The INA219 is designed for compatibility with hot
the Conversion Ready bit (Status Register, CNVR bit)
swap controllers such the TI TPS2490. The TPS2490
is provided to help co-ordinate one-shot or triggered
uses a high-side shunt with a limit at 50mV; the
conversions. The Conversion Ready bit is set after all
INA219 full-scale range of 40mV enables the use of
conversions, averaging, and multiplication operations
the same shunt for current sensing below this limit.
are complete.
When sensing is required at (or through) the 50mV
sense point of the TPS2490, the PGA of the INA219
The Conversion Ready bit clears under these
can be set to ÷2 to provide an 80mV full-scale range.
conditions:
1. Writing to the Configuration Register, except
Filtering and Input Considerations
when configuring the MODE bits for Power Down
or ADC off (Disable) modes;
Measuring current is often noisy, and such noise can
be difficult to define. The INA219 offers several
2. Reading the Status Register; or
options for filtering by choosing resolution and
3. Triggering a single-shot conversion with the
averaging in the Configuration Register. These
Convert pin.
filtering options can be set independently for either
voltage or current measurement.
Power Measurement
The internal ADC is based on a delta-sigma (ΔΣ)
Current and bus voltage are converted at different
front-end with a 500kHz (±30%) typical sampling rate.
points in time, depending on the resolution and
This architecture has good inherent noise rejection;
averaging mode settings. For instance, when
however, transients that occur at or very close to the
configured for 12-bit and 128 sample averaging, up to
sampling rate harmonics can cause problems.
68ms in time between sampling these two values is
Because these signals are at 1MHz and higher, they
possible. Again, these calculations are performed in
can be dealt with by incorporating filtering at the input
the background and do not add to the overall
of the INA219. The high frequency enables the use of
conversion time.
low-value series resistors on the filter for negligible
effects on measurement accuracy. In general, filtering
PGA Function
the INA219 input is only necessary if there are
If larger full-scale shunt voltages are desired, the
transients at exact harmonics of the 500kHz (±30%)
INA219 provides a PGA function that increases the
sampling rate (>1MHz). Filter using the lowest
full-scale range up to 2, 4, or 8 times (320mV).
possible series resistance and ceramic capacitor.
Additionally, the bus voltage measurement has two
Recommended values are 0.1μF to 1.0μF. Figure 20
full-scale ranges: 16V or 32V.
shows the INA219 with an additonal filter added at
the input.
Figure 20. INA219 with Input Filtering
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Product Folder Link(s): INA219