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 2.9s. The measurement is averaged and presented on the analog output with a full-scale range of 3V, 2V, 1.5V, or 1.0V.
Features
- Configurable measurement type output: power, current, or bus voltage
- Configurable voltage output (3V, 2V, 1.5V, 1V)
- 100 mV full-scale current sense voltage range
- Second-order delta-sigma ADC with 11-bit or 14-bit resolution
- 1 percent power measurement accuracy
- +/- 0.4 percent 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 3.0V to 5.5V)
- Bus range: 0V to 32V
- 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 |
| SENSE+ | VBUS/VSENSE+ input | AIO40 |
| SENSE- | VSENSE- input | AIO40 |
| 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 of 40 V. |
| AIO2 | Analog Input/Output - this pin is used as an I/O for analog signals. Maximum voltage of 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).
