Jian Li and Gina Le, Linear Technology
Design Note 524
Digital Power System Management: Set, Monitor, Change, and Log Power
Managing power and implementing flexibility in a high rail count circuit board can be challenging, requiring hands-on probing with digital voltmeters and oscilloscopes, and often rework of PCB components. To simplify power management, especially from a remote location, there is a trend to configure and monitor power via a digital communications bus. Digital power system management (PSM) enables on-demand telemetry capability to set, monitor, change and log power parameters.
Dual μModule Regulator with Precision READ/WRITE of Power Parameters
The LTM4676 is a dual 13 A output constant frequency switching mode DC/DC μModule (micromodule) regulator (Figure 1). In addition to delivering power at a point-of-load, the LTM4676 features configurability and telemetry-monitoring of power and power management parameters over PMBus – an open standard I2C-based digital serial interface protocol. The LTM4676 combines best-in-class analog switching regulator performance with precision mixed signal data acquisition. It features ±1% maximum DC output voltage error and ±2.5% current read back accuracy over temperature (TJ = –40 °C to 125 °C), and integrated 16-bit delta-sigma ADC and EEPROM.
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| Figure 1. | LTM4676: Dual 13 A Output μModule Regulator with PMBus Interface. |
The LTM4676’s 2-wire serial interface allows outputs to be margined, tuned and ramped up and down at programmable slew rates with sequencing delay times. Input and output currents and voltages, output power, temperature, uptime and peak values are readable. The device is comprised of fast, dual analog control loops, precision mixed signal circuitry, EEPROM, power MOSFETs, inductors and supporting components housed in a 16 mm × 16 mm × 5.01 mm BGA (ball grid array) package.
The LTM4676 operates from a 4.5 V to 26.5 V input supply and steps down VIN to two outputs ranging from 0.5 V to 5.4 V. Two outputs can current share to provide up to 26 A (i.e., 13 A + 13 A as one output).
Internal or External Compensation
The LTM4676 offers both internal or external compensation, which can optimize the transient response over a wide operating range. Figure 2 shows that the peak-to-peak output voltage is only 94 mV with a 50% load step.
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| Figure 2. | Transient Response of the LTM4676 in Figure 1 at VIN = 12V, VOUT1 = 1.8 V, IO = 6.5 A ~ 13 A |
Current Share for up to 100 A at 1 VOUT
The LTM4676 uses a constant frequency peak current mode control architecture, which offers a cycle-by-cycle current limit and easy current sharing among multiple phases. Paralleling modules can achieve much higher output current capability. For example, four LTM4676 μModule regulators can be paralleled to provide up to 100 A output current. Figure 3 shows the thermal picture.
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| Figure 3. | Four LTM4676 Current Sharing: Thermal Picture at VIN = 12 V, VOUT = 1.0 V/100 A, 300 LFM Airflow. |
With 300 LFM of airflow, the hot spot temperature rise is only 64.3 °C. The even thermal distribution among modules is due to excellent current sharing performance. Figure 4 is a photo of the demo board with four LTM4676 μModule regulators assembled to provide 100 A at 1 V.
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| Figure 4. | Four LTM4676, Each in a 16 mm × 16 mm × 5.01 mm LGA Package Deliver 100 A at 1 VOUT. |
Conclusion
Linear Technology’s digital power system management (PSM) products provide users with critical power-related data. One can access load current, input current, output voltages, compute power consumption, efficiency, and access other power management parameters via a digital bus. This enables predictive analytics, minimizes operating costs, increases reliability and ensures smart energy management decisions can be made.
On-demand digital control and monitoring of system power with the LTM4676 eliminates PCB layout and circuit component manipulation and accelerates system characterization, optimization and data mining during prototyping, deployment and field operation.
