INA239 datasheet(15/47 Pages) TI

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7.3.3 Low Bias Current

The INA239-Q1 features very low input bias current which provides several benefits. The low input bias current

of the INA239-Q1 reduces the current consumed by the device in both active and shutdown state. Another

benefit of low bias current is that it allows the use of input filters to reject high-frequency noise before the signal

is converted to digital data. In traditional digital current-sense amplifiers, the addition of input filters comes at

the cost of reduced accuracy. However, as a result of the low bias current, the reduction in accuracy due to

input filters is minimized. An additional benefit of low bias current is the ability to use a larger shunt resistor to

accurately sense smaller currents. Use of a larger value for the shunt resistor allows the device to accurately

monitor currents in the sub-mA range.

The bias current in the INA239-Q1 is the smallest when the sensed current is zero. As the current starts to

increase, the differential voltage drop across the shunt resistor increases which results in an increase in the bias

current as shown in Input Bias Current vs. Differential Input Voltage.

7.3.4 High-Precision Delta-Sigma ADC

The integrated ADC is a high-performance, low-offset, low-drift, delta-sigma ADC designed to support

bidirectional current flow at the shunt voltage measurement channel. The measured inputs are selected through

the high-voltage input multiplexer to the ADC inputs as shown in Figure 7-1. The ADC architecture enables

lower drift measurement across temperature and consistent offset measurements across the common-mode

voltage, temperature, and power supply variations. A low-offset ADC is preferred in current sensing applications

to provide a near 0-V offset voltage that maximizes the useful dynamic range of the system.

The INA239-Q1 can measure the shunt voltage, bus voltage, and die temperature, or a combination of any

based on the selected MODE bits setting in the ADC_CONFIG register. This permits selecting modes to convert

only the shunt voltage or bus voltage to further allow the user to configure the monitoring function to fit the

specific application requirements. When no averaging is selected, once an ADC conversion is completed, the

converted values are independently updated in their corresponding registers where they can be read through

the digital interface at the time of conversion end. The conversion time for shunt voltage, bus voltage, and

temperature inputs are set independently from 50 µs to 4.12ms depending on the values programmed in the

ADC_CONFIG register. Enabled measurement inputs are converted sequentially so the total time to convert

all inputs depends on the conversion time for each input and the number of inputs enabled. When averaging

is used, the intermediate values are subsequently stored in an averaging accumulator, and the conversion

sequence repeats until the number of averages is reached. After all of the averaging has been completed, the

final values are updated in the corresponding registers that can then be read. These values remain in the data

output registers until they are replaced by the next fully completed conversion results. In this case, reading the

data output registers does not affect a conversion in progress.

The ADC has two conversion modes—continuous and triggered—set by the MODE bits in ADC_CONFIG

the output registers as described above in an indefinite loop. In triggered-conversion mode, the ADC will convert

the input measurements as described above, after which the ADC will go into shutdown mode until another

single-shot trigger is generated by writing to the MODE bits. Writing the MODE bits will interrupt and restart

triggered or continuous conversions that are in progress. Although the device can be read at any time, and

the data from the last conversion remains available, the Conversion Ready flag (CNVRF bit in DIAG_ALRT

is completed.

The Conversion Ready flag (CNVRF) clears under these conditions:

• Writing to the ADC_CONFIG register (except for selecting shutdown mode); or

• Reading the DIAG_ALRT Register

While the INA239-Q1 device is used in either one of the conversion modes, a dedicated digital engine is

calculating the current and power values in the background as described in Section 7.3.2. All of the calculations

are performed in the background and do not contribute to conversion time.

For applications that must synchronize with other components in the system, the INA239-Q1 conversion can be

delayed by programming the CONVDLY bits in CONFIG register in the range between 0 (no delay) and 510

www.ti.com

INA239-Q1

SLYS028A – MAY 2020 – REVISED JUNE 2021

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