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A look inside Linear's synchronous step-down regulator

01 Apr 2016  | Steve Taranovich

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Current mode control in power supply architectural design brings a number of advantages. These include improved load/line regulation, cycle-by-cycle current limiting and protection, and balanced flux.

A recent product in the market that offers current mode control is Linear Technology Corp.'s LTC7130, a constant frequency peak current mode synchronous step-down DC/DC converter including temperature-compensated ultra-low DC Resistance (DCR) current sensing and clock synchronisation. This design architecture eases compensation for power supply designers and allows for a simpler capability of directly paralleling multiple ICs for higher current capability. Signal-to-noise ratio (SNR) of the current sense signal has been enhanced in this architecture which allows for the the use of a very low DC resistance power inductor which maximises efficiency in a high current design.

The integrated low RDS(on) MOSFETs allow for a smaller solution with less board real estate needed.

Light load performance

The regulator can be directed to run at a high efficiency Burst Mode, a constant-frequency pulse-skipping mode or a forced continuous conduction mode via the MODE/PLLIN pin.

Added performance

The DC/DC's 90ns minimum on-time enables a high step-down ratio power supply at high frequency operation. The operating frequency can be varied from 250kHz to 770kHz and synchronised to an external clock. The IC's total differential output voltage accuracy is ±0.5% over the full –40°C to 125°C operating junction temperature range.

Added features

Some additional features include a high speed differential remote sense amplifier, programmable output current limit, output short-circuit protection with soft recovery, programmable soft-start/tracking, EXTVCC for reduced power dissipation and a fault indicator for output UV/OV conditions.

Current sensing

AC and DC currents are accurately and effectively sensed in this device which can operate with a very tiny sense signal from a low value of inductor DCR (The DC copper winding resistance of the inductor) of 1 mΩ or lower in high current inductors.

Enabling a wide variety of applications

The improved SNR also improves switching jitter often found in low DCR applications and also improves the accuracy of the current limit function. The IC's 4.5V to 20V input range is useful in a wide variety of applications, including most intermediate bus voltages, and is compatible with many battery types. The integrated N-channel MOSFETs can deliver continuous load currents up to 20A at output voltages spanning 0.6V to 5.5V, this is perfect for point-of-load applications like high current / low voltage DSP / FPGA / ASIC reference designs. Other applications include telecom/datacom systems, distributed power architectures and general high power density systems.

Demo board

The LTC7130 has a nice demo board, the DC2341A. See the 20A buck below with mΩ inductor DCR sensing with an input range of 4.5V to 20V and a Vout of 1.5V@20A.

Thermal performance

The DC2341A demo board has a really good thermal design. See figure below.

Thermal derating has been shown to be excellent both with and without airflow and heatsinks. See image below.

Package, grades and pricing

The IC is available in a thermally-enhanced 6.25mm × 7.5mm × 2.22mm BGA package, with both RoHS lead-free and leaded SnPb (63/37) finishes. The E-and I-grades are guaranteed from –40°C to 125°C operating junction temperature range. The 1,000-piece price starts at $7.95 each for the E grade.

Pricing is for budgetary use only and may differ due to local duties, taxes, fees and exchange rates.




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