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Power Measurement

Peak-Hold Registers

INA209

SBOS403B – JUNE 2007 – REVISED MARCH 2009 .........................................................................................................................................................

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When the INA209 is in the normal operating mode The Conversion Ready bit clears under these

(that is, MODE bits of the Configuration Register are conditions:

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

1. Writing to the Configuration Register, except

voltage up to the number set in the shunt voltage

when configuring the MODE bits for Power Down

averaging function (Configuration Register, SADC

or ADC off (Disable) modes;

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

2. Reading the Status Register; or

the number set in the bus voltage averaging

3. Triggering a single-shot conversion with the

(Configuration Register, BADC bits). The Mode

Convert pin.

control in the Configuration Register also permits

selecting modes to convert only voltage or current,

either continuously or in response to an event

(triggered).

Current and bus voltage are converted at different

points in time, depending on the resolution and

All current and power calculations are performed in

averaging mode settings. For instance, when

the background and do not contribute to conversion

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

time; conversion times shown in the Electrical

68ms in time between sampling these two values is

Characteristics table can be used to determine the

possible. Again, these calculations are performed in

actual conversion time.

the background and do not add to the overall

Power-Down mode reduces the quiescent current

conversion time.

and turns off current into the INA209 inputs, avoiding

any supply drain. Full recovery from Power-Down

requires 40 µ s. ADC Off mode (set by the

Configuration Register, MODE bits) stops all Shunt voltage peak registers hold the lowest and

conversions. highest converted reading for the shunt value. The

shunt value may be either positive or negative; as a

In triggered mode, the external Convert line becomes

result, there is a need for a sign bit in either register.

active. Convert commands are initiated by taking the

For instance, the Shunt Voltage Positive Peak

Convert line low for a minimum of 4 µ s. The Convert

line may be connected high when unused. Any

in most unidirectional current measurement

re-trigger of the Convert line during a conversion is

applications, the Shunt Voltage Negative Peak

ignored, and the Convert line state is disregarded

until the conversion ends. There are several available

certain conditions can occur in normally unidirectional

triggered modes; however, all conversions are

systems that cause a negative polarity across the

performed repeatedly up to the number set in the

shunt; these events are recorded in the Shunt

Averaging function (Configuration Register, BADC

Voltage Negative Peak Register.

and SADC bits).

Peak-hold registers do not record conditions that

If the Convert line is held low, writing any of the

trigger a Critical Comparator shutdown. A Critical

triggered convert modes into the Configuration

Comparator shutdown occurs within 5 µ s of detecting

a critical condition, while the ADC conversion

programmed into the register) triggers a single-shot

necessary to record a peak-hold requires 532 µ s.

conversion.

Therefore, a system shutdown removes the fault

before the analog-to-digital conversion (ADC) can

Although the INA209 can be read at any time, and

record it.

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.

Product Folder Link(s): INA209