ina219 datasheet

Supply
Load
R 10W
FILTER
R 10W
FILTER
0.1 F to 1 Fm m
Ceramic Capacitor
Data (SDA)
3.3V Supply
Clock (SCL)
´
Power Register
Current Register
I C-/SMBUS-
Compatible
Interface
2
Voltage Register
V
IN+
V
IN-
ADC
PGA
INA219
GND
A0
A1
Supply Voltage
V
S
R
SHUNT
INA219
www.ti.com SBOS448G –AUGUST 2008–REVISED DECEMBER 2015
8.4 Device Functional Modes
8.4.1 Filtering and Input Considerations
Measuring current is often noisy, and such noise can be difficult to define. The INA219 offers several options for
filtering by choosing resolution and averaging in the Configuration register. These filtering options can be set
independently for either voltage or current measurement.
The internal ADC is based on a delta-sigma (ΔΣ) front-end with a 500-kHz (±30%) typical sampling rate. This
architecture has good inherent noise rejection; however, transients that occur at or very close to the sampling
rate harmonics can cause problems. Because these signals are at 1 MHz and higher, they can be dealt with by
incorporating filtering at the input of the INA219. The high frequency enables the use of low-value series resistors
on the filter for negligible effects on measurement accuracy. In general, filtering the INA219 input is only
necessary if there are transients at exact harmonics of the 500-kHz (±30%) sampling rate (>1 MHz). Filter using
the lowest possible series resistance and ceramic capacitor. Recommended values are 0.1 to 1 μF. Figure 14
shows the INA219 with an additional filter added at the input.
Figure 14. INA219 With Input Filtering
Overload conditions are another consideration for the INA219 inputs. The INA219 inputs are specified to tolerate
26 V across the inputs. A large differential scenario might be a short to ground on the load side of the shunt. This
type of event can result in full power-supply voltage across the shunt (as long the power supply or energy
storage capacitors support it). It must be remembered that removing a short to ground can result in inductive
kickbacks that could exceed the 26-V differential and common-mode rating of the INA219. Inductive kickback
voltages are best dealt with by zener-type transient-absorbing devices combined with sufficient energy storage
capacitance.
In applications that do not have large energy storage electrolytics on one or both sides of the shunt, an input
overstress condition may result from an excessive dV/dt of the voltage applied to the input. A hard physical short
is the most likely cause of this event, particularly in applications with no large electrolytics present. This problem
occurs because an excessive dV/dt can activate the ESD protection in the INA219 in systems where large
currents are available. Testing has demonstrated that the addition of 10-Ω resistors in series with each input of
the INA219 sufficiently protects the inputs against dV/dt failure up to the 26-V rating of the INA219. These
resistors have no significant effect on accuracy.
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