INA220 datasheet(14/35 Pages) TI

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Power-Up Conditions

BASIC ADC FUNCTIONS

Power Measurement

PGA Function

Compatibility with TI Hot Swap Controllers

Filtering and Input Considerations

INA220

SBOS459B – JUNE 2009 – REVISED JUNE 2009 ............................................................................................................................................................. www.ti.com

The

Conversion

Ready

bit

clears

under

these

conditions:

Power-up conditions apply to a software reset via the

1. Writing to the Configuration Register, except

RST bit (bit 15) in the Configuration Register, or the

when configuring the MODE bits for Power Down

Two-Wire bus General Call Reset.

or ADC off (Disable) modes;

2. Reading the Status Register; or

3. Triggering a single-shot conversion with the

The two analog inputs to the INA220, VIN+ and VIN–,

Convert pin.

connect to a shunt resistor in the bus of interest. Bus

voltage is measured at VBUS pin. The INA220 is

typically powered by a separate supply from +3V to

+5.5V. The bus being sensed can vary from 0V to

Current and bus voltage are converted at different

26V.

There

are

special

considerations

for

points in time, depending on the resolution and

power-supply sequencing (for example, a bus voltage

averaging

mode

settings.

For

instance,

when

can be present with the supply voltage off, and

configured for 12-bit and 128 sample averaging, up to

vice-versa). The INA220 senses the small drop

68ms in time between sampling these two values is

across the shunt for shunt voltage, and senses the

possible. Again, these calculations are performed in

voltage with respect to ground from VBUS for the bus

the background and do not add to the overall

voltage.

conversion time.

When the INA220 is in the normal operating mode

(that is, MODE bits of the Configuration Register are

set to '111'), it continuously converts the shunt

If larger full-scale shunt voltages are desired, the

voltage up to the number set in the shunt voltage

INA220 provides a PGA function that increases the

averaging function (Configuration Register, SADC

full-scale range up to 2, 4, or 8 times (320mV).

bits). The device then converts the bus voltage up to

Additionally, the bus voltage measurement has two

the number set

the

bus

voltage

averaging

full-scale ranges: 16V or 32V.

(Configuration Register, BADC bits). The Mode

control in the Configuration Register also permits

selecting modes to convert only voltage or current,

The INA220 is designed for compatibility with hot

either continuously or in response to an event

swap controllers such the TI TPS2490. The TPS2490

(triggered).

uses a high-side shunt with a limit at 50mV; the

All current and power calculations are performed in

INA220 full-scale range of 40mV enables the use of

the background and do not contribute to conversion

the same shunt for current sensing below this limit.

time; conversion times shown in the Electrical

When sensing is required at (or through) the 50mV

Characteristics table can be used to determine the

sense point of the TPS2490, the PGA of the INA220

actual conversion time.

can be set to ÷2 to provide an 80mV full-scale range.

Power-Down mode reduces the quiescent current

and turns off current into the INA220 inputs, avoiding

any supply drain. Full recovery from Power-Down

Measuring current is often noisy, and such noise can

requires

µs. ADC Off mode (set by the

be difficult to define. The INA220 offers several

Configuration

MODE

bits)

stops

all

options for filtering by choosing resolution and

conversions.

averaging

the

Configuration

These

filtering options can be set independently for either

In triggered mode, writing any of the triggered convert

voltage or current measurement.

modes into the Configuration Register (even if the

desired mode is already programmed

into

the

The internal ADC is based on a delta-sigma (

ΔΣ)

front-end with a 500kHz (±30%) typical sampling rate.

This architecture has good inherent noise rejection;

Although the INA220 can be read at any time, and

however, transients that occur at or very close to the

the data from the last conversion remain available,

sampling

rate

harmonics

can

cause

problems.

the Conversion Ready bit (Status Register, CNVR bit)

Because these signals are at 1MHz and higher, they

is provided to help co-ordinate one-shot or triggered

can be dealt with by incorporating filtering at the input

conversions. The Conversion Ready bit is set after all

of the INA220. The high frequency enables the use of

conversions, averaging, and multiplication operations

low-value series resistors on the filter for negligible

are complete.

effects on measurement accuracy. In general, filtering

space

the INA220 input is only necessary if there are

transients at exact harmonics of the 500kHz (±30%)

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