Jian Li, Yingyi Yan and Marvin Macairan, Linear Technology
Design Note 542
Introduction
The LTM4675 is a dual 9 A or single 18 A step-down μModuleR (micromodule) DC/DC regulator featuring remote configurability and telemetry monitoring of power system management (PSM) parameters over PMBus – an open standard I2C-based digital interface protocol. Its 16 mm × 11.9 mm × 3.51 mm BGA package includes analog control loops, precision mixed-signal circuitry, EEPROM, power MOSFETs, inductors and supporting components. It features a wide 4.5 V to 17 V input voltage range, and a 0.5 V to 5.5 V output voltage range with ±0.5% DC accuracy over temperature. LTM4675’s power outputs can be digitally adjusted, margined and powered up/down at programmable slew rates and sequencing delay times. Maximum turn-on time is 70 ms. Telemetry read back parameters include VIN, IIN, VOUT, IOUT, temperature, running peak values, uptime, faults and warnings. Current read back accuracy is ±2.5% at 9 A load over temperature.
The LTM4675 facilitates the design of high efficiency, high power density and high reliability solutions for telecom, datacom and storage systems, plus industrial and instrumentation power supplies. The LTM4675 is offered in a 16 mm × 11.9 mm × 3.51 mm BGA package available with SnPb or RoHS compliant terminal finish.
Dual 9A μModule Regulator with Digital Power System Management
Figure 1 shows a typical LTM4675 application. The input voltage range is 5.75 V to 17 V, and the outputs are 1 V/ 9A and 1.8 V/9 A. Figure 2 shows the efficiency for each output of the LTM4675 for a variety of output voltages vs load current. The LTM4675 can achieve high efficiency over a wide operating range, with high reliability. Figure 3 shows that the maximum case temperature is 84.1 °C when the module is running with a 12 V input, 1 V/9 A and 1.8 V/9 A outputs, without airflow.
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| Figure 1. | 9 A, 1 V and 9 A, 1.8 V Output DC/DC μModule Regulator with Serial Interface. |
The LTM4675 offers internal compensation or external compensation, which can be used to optimize the transient response to load current steps over a wide operating range.
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| Figure 2. | LTM4675 Single Channel Efficiency at VIN = 12 V. |
The LTM4675 supports a PMBus-compliant SMBus serial interface up to 400 kHz. Readable data includes input and output voltages, currents, temperatures, running peak values, uptime, faults, warnings and an onboard EEPROM fault log record. Writable data and configurable parameters include output voltage, voltage sequencing and margining, digital soft-start/ stop ramp, OV/UV/OT, UVLO, frequency and phasing. The LTM4675 guarantees high accuracy telemetry read back with an integrated 16-bit ΔΣ ADC.
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| Figure 3. | Thermal Performance of LTM4675 at VIN = 12 V, VOUT0 = 1 V/9 A, VOUT1 = 1.8 V/9 A, No Airflow, Tested on DC2053A. Maximum Temperature Rise = 61.1°C, TA = 23 °C. |
Multi-Module Operation for High Current Applications
The LTM4675 utilizes a constant frequency peak current mode control architecture, which enables cycle-by-cycle current limit and easy current sharing among phases when the channels are operated in parallel. For higher output current capability, it’s easy to parallel multiple LTM4675 modules. Furthermore, the LTM4675 can be used as a master to drive non- PSM power modules to provide much higher output current. For example, the LTM4675 can drive three LTM4630s to provide up to 125 A output current. Figure 4 shows the thermal picture of this application. With 400 LFM of airflow, the hot spot temperature rise is only 66.2 °C. The uniform thermal distribution among the modules is due to excellent current sharing performance.
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| Figure 4. | Thermal Picture at VIN = 12 V, VO = 1.0 V/125 A, 400 LFM Airflow, Maximum Temperature Rise = 66.2 °C, TA = 23 °C. |
Conclusion
LTM4675 is a high efficiency and high power density μModule regulator with built-in digital power system management. With all of the features mentioned above, the LTM4675 is ideal for telecom, datacom and storage systems, industrial and instrumentation applications.
