introduction
The LTC3883 is a single-phase synchronous step-down DC/DC controller with a PMBus interface for digital control and monitoring of primary regulator parameters. The device includes an integrated MOSFET gate driver that can operate independently or in conjunction with other Linear Technology devices that support PMBus in digital management systems. The LTC3883 has the following features:
·4.5V~24V input voltage and 0.5V~5.5V output voltage range
• ±0.5% output voltage accuracy over the entire operating temperature range of –40°C to 125°C
• PMBus interface for programmable voltage, current limit, sequencing, margining, OV/UV threshold, frequency synchronization and fault logging
Telemetry readback parameters include VIN, IIN, VOUT, IOUT, temperature, and fault
External voltage divider for setting chip address, default switching frequency and output voltage
·Input current detection and inductor DCR auto calibration
1.8V/30A single-phase digital power supply with IIN detection
Figure 1 shows a 7V to 14V input, 1.8V/30A output application circuit with inductor DCR current sensing. To improve the accuracy of DCR current sensing, the LTC3883 senses the inductor temperature and compensates for the temperature coefficient of the winding resistance. This method ensures the accuracy of the readback current and overcurrent limits. The LTC3883's control loop uses peak current mode control for fast transient response and cycle-by-cycle current limiting. Figure 2 shows a typical waveform for a 10A load step transient with a maximum deviation (relative to the nominal value) of only 60mV.
Figure 1: 1.8V/30A single-phase digital power supply with IIN detection 
Figure 2: Transient performance of a 10A load step
Input current detection
The LTC3883 features input current sensing through a resistor in series with the input side of the buck converter (5mΩ sense resistor as shown in Figure 1). The sense voltage is converted to a power stage input current by the LTC3883's 16-bit internal ADC. In addition, an internal IC sense resistor is responsible for detecting the supply current of the chip on VIN, so it can provide input current measurements at the chip and power stage.
Inductor DCR auto calibration
The problem with conventional inductor DCR current sensing is that DCR tolerances can be as high as ±10%, which greatly limits current readback accuracy. To solve this problem, the LTC3883 uses a proprietary inductor DCR auto-calibration feature. Figure 3 shows a simplified schematic of the circuit. The LTC3883 accurately measures the input current IIN, duty cycle (D), and current sense voltage (VCS) and calibrates the actual DCR value according to the following relationship:
With this automatic calibration method, the output current readback accuracy can be controlled within 3%, independent of the inductor DCR tolerance.
LTpowerPlayTM GUI
All power system management functions are controlled by the PC-based graphical user interface LTpowerPlay, which is compatible with all of Linear Technology's power system management products. With LTpowerPlay, designers can easily set up and control the entire power system without writing a single line of code. With this tool, it's easy to configure any chip on the bus, check system status, read telemetry data, check fault status, and control power sequencing.
Figure 3: DCR Auto Calibration
in conclusion
The LTC3883 combines a best-in-class analog DC/DC controller with complete power system management and high-precision data converters for unprecedented performance and control. Multiple LTC3883s can be used with other Linear Technology PMBus products to optimize multi-rail power systems. The powerful LTpowrPlay software simplifies the development of complex power systems. If dual output is required, the LTC3880 can be used, which also has power system management capabilities.
——This article is selected from the “EE Design†column of “Electronics Technology Special Issue†in March. Please indicate the source, please do not hesitate!
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