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.
Features
- 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 |
| 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 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. |
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).
