INA209_15 Datasheet, PDF (16/50 Pages) Texas Instruments – High-Side Measurement, Bi-Directional Current/Power Monitor with I2C Interface

INA209
SBOS403B – JUNE 2007 – REVISED MARCH 2009 ......................................................................................................................................................... www.ti.com
When the INA209 is in the normal operating mode
(that is, MODE bits of the Configuration Register are
set to '111'), it continuously converts the shunt
voltage up to the number set in the shunt voltage
averaging function (Configuration Register, SADC
bits). The device then converts the bus voltage up to
the number set in the bus voltage averaging
(Configuration Register, BADC bits). The Mode
control in the Configuration Register also permits
selecting modes to convert only voltage or current,
either continuously or in response to an event
(triggered).
All current and power calculations are performed in
the background and do not contribute to conversion
time; conversion times shown in the Electrical
Characteristics table can be used to determine the
actual conversion time.
Power-Down mode reduces the quiescent current
and turns off current into the INA209 inputs, avoiding
any supply drain. Full recovery from Power-Down
requires 40µs. ADC Off mode (set by the
Configuration Register, MODE bits) stops all
conversions.
In triggered mode, the external Convert line becomes
active. Convert commands are initiated by taking the
Convert line low for a minimum of 4µs. The Convert
line may be connected high when unused. Any
re-trigger of the Convert line during a conversion is
ignored, and the Convert line state is disregarded
until the conversion ends. There are several available
triggered modes; however, all conversions are
performed repeatedly up to the number set in the
Averaging function (Configuration Register, BADC
and SADC bits).
If the Convert line is held low, writing any of the
triggered convert modes into the Configuration
Register (even if the desired mode is already
programmed into the register) triggers a single-shot
conversion.
Although the INA209 can be read at any time, and
the data from the last conversion remain available,
the Conversion Ready bit (Status Register, CNVR bit)
is provided to help co-ordinate one-shot or triggered
conversions. The Conversion Ready bit is set after all
conversions, averaging, and multiplication operations
are complete.
The Conversion Ready bit clears under these
conditions:
1. Writing to the Configuration Register, except
when configuring the MODE bits for Power Down
or ADC off (Disable) modes;
2. Reading the Status Register; or
3. Triggering a single-shot conversion with the
Convert pin.
Power Measurement
Current and bus voltage are converted at different
points in time, depending on the resolution and
averaging mode settings. For instance, when
configured for 12-bit and 128 sample averaging, up to
68ms in time between sampling these two values is
possible. Again, these calculations are performed in
the background and do not add to the overall
conversion time.
Peak-Hold Registers
Shunt voltage peak registers hold the lowest and
highest converted reading for the shunt value. The
shunt value may be either positive or negative; as a
result, there is a need for a sign bit in either register.
For instance, the Shunt Voltage Positive Peak
Register in most systems records a positive voltage;
in most unidirectional current measurement
applications, the Shunt Voltage Negative Peak
Register also records a positive voltage. However,
certain conditions can occur in normally unidirectional
systems that cause a negative polarity across the
shunt; these events are recorded in the Shunt
Voltage Negative Peak Register.
Peak-hold registers do not record conditions that
trigger a Critical Comparator shutdown. A Critical
Comparator shutdown occurs within 5µs of detecting
a critical condition, while the ADC conversion
necessary to record a peak-hold requires 532µs.
Therefore, a system shutdown removes the fault
before the analog-to-digital conversion (ADC) can
record it.
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