PAC1921 Current Power Sensor

PAC1921 is a high-side current/power sensor with a 2-wire bus and a configurable analog output that can present power, current, or voltage. The PAC1921 is designed for power measurement and diagnostic systems that cannot allow for latency when performing high-speed power management. Measurements are accumulated in large lossless registers, allowing for integration periods of 500 μs to 2.9 s. The measurement is averaged and presented on the analog output with a full-scale range of 3 V, 2 V, 1.5 V, or 1.0 V.

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  • Configurable measurement type output: power, current, or bus voltage
  • Configurable voltage output (3 V, 2 V, 1.5 V, 1 V)
  • 100 mV full-scale current sense voltage range
  • Second-order delta-sigma ADC with 11-bit or 14-bit resolution
  • 1% power measurement accuracy
  • +/- 0.4% current measurement accuracy (Max.)
  • 0.9 ms - 2,900 ms effective sampling interval
  • Auto-zero offset
  • Auto sleep state: automatically shifts to low-power state (3.5 μA)
  • VDD = 3.3 V nominal (operational range 3.0 V to 5.5 V)
  • Bus range: 0 V to 32 V
  • No input filters required
  • Interface: SMBus/I²C

Target Applications

  • Diagnostic Equipment
  • Servers
  • Power Supplies
  • Industrial and Power Management Systems
  • Notebook and Desktop Computers

Block Diagram


Pin Descriptions

Symbol Function Type
VDD Positive Power Supply Voltage Power
OUT Output Voltage Measurement AIO5
GND Ground Power
ADDR_SEL Select SMBus/I²C Address AIO2
RESERVED Reserved for future use (connect to VDD for SMBus functionality) DI (5 V)
READ/INT Controls power states DI
SM_DATA SM_DATA: SMBus/I²C Data - requires pull-up resistor DIOD
SM_CLK SM_CLK: SMBus/I²C Clock - requires pull-up resistor DI (5 V)
EP Not internally connected but recommend grounding N/A
Pin Type Description
Power This pin is used to power to the device.
AIO40 Analog Input/Output - this pin is used as an I/O for analog signals. Maximum voltage is 40 V.
AIO2 Analog Input/Output - this pin is used as an I/O for analog signals. Maximum voltage is 2 V.
DI Digital Input - this pin is used for digital inputs.
DIOD Digital Input/Output Open-Drain - this pin is used for digital I/O and is open-drain.
PAC1921 - A World First in High-Side Current/Power Sensors

Application Example

The figure below shows a system diagram using the PAC1921 in SMBus mode. The OUT pin supplies data for systems that cannot tolerate the latencies inherent in embedded communications buses. MCU-based systems, such as PIC® Microcontrollers (MCUs) equipped with Analog-to-Digital Converters (ADC) inputs can sample the value presented on the OUT pin for immediate use in thermal or power control algorithms. Output values are also available in a digital format via the SMBus interface. The PAC1921 contains a high-side precision current-sensing circuit and a precision bus voltage measurement circuit. The current-sensing circuit contains a differential amplifier that continuously measures the voltage (VSENSE) developed across an external sense resistor (RSENSE) to represent the high-side supply current. The full-scale range of VSENSE is from 0 mV to 100 mV. For power, the current and voltage data are multiplied and accumulated, scaled with two digital gain parameters, then applied to the OUT pin through a 10-bit DAC and a gain output buffer for the output Full-Scale-Range (FSR).

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