Our goal? 90% efficiency!

The LTC7852/LTC7852-1 are designed to achieve high efficiency. Each phase of the LTC7852 does not use an internal gate driver and can generate a PWM output that connects to a power module, DrMOS, or an external gate driver and discrete MOSFET. DrMOS devices integrate gate drivers and MOSFETs in one package to achieve an overall smaller solution size and higher efficiency. They are mainly suitable for 12 V input voltage. The external gate driver and MOSFET have excellent thermal performance and can operate at higher input voltages. The LTC7852 uses a sub-mΩ DCR sensing architecture to accurately sense current with a DCR value of only 0.2 mΩ, which can significantly reduce conduction losses. The LTC7852-1 is designed to be used with DrMOS devices, which provide their own current sensing signal.

Each output is differentially sensed over a voltage range of 0.5 V to 2.0 V (2.0 V limit applies only to LTC7852), with an overall regulation accuracy of ±0.5%. Because the LTC7852 and LTC7852-1 are biased from an external 5 V supply, rather than from the input voltage, the converter's input voltage range is not limited by the IC. Its switching frequency range is 250 kHz to 1.25 MHz, but its 40 ns minimum on-time enables high step-down ratios.

3+3, 4+2, and 5+1 dual output phase configurations can be selected via the PHCFG pin. In the 3+3 configuration, two outputs can be paralleled for a 6-phase converter with a maximum load current of 240 A. Using one 6-phase controller instead of two 3-phase controllers or three 2-phase controllers greatly simplifies the design and layout. Only two controllers are required to achieve up to 12-phase operation.

The LTC7852 is available in a 5 mm × 6 mm GQFN package, and the LTC7852-1 is available in a 4 mm × 5 mm QFN package.

Figure 1 shows a 6-phase 1.0 V/200 A LTC7852 converter switching at 400 kHz with a 12 V input. The power stage for each phase consists of a 5 mm × 5 mm DrMOS and a 0.25 µH ferrite inductor with a typical DCR of 0.325 mΩ, resulting in a full-load efficiency of 90.0% (Figure 2). At full load at room temperature, the hotspot temperature is 78°C with 200 LFM airflow (Figure 3). The temperature difference between the inductors is less than 6°C due to strict current sharing.

The LTC7852 uses a proprietary peak current mode sub-mΩ DCR sensing architecture to improve the signal-to-noise ratio of the current sense signal. A DCR sensing filter in the inductor provides an amplified AC signal to the SNSP and SNSN pins. A second filter is cascaded with the first to provide a DC signal to the SNSP and SNSAVG pins. The LTC7852 amplifies the DC signal and sums it with the AC signal to reconstruct the signal. The reconstructed signal is 5 times the original signal, allowing stable and clean operation at DCR values ​​as low as 0.2 mΩ.

The LTC7852's IMON1 and IMON2 signals generate signals proportional to the load current of the corresponding channel and use the V1P5 pin as a voltage reference. This signal can be used by a power monitor or ADC and microcontroller for load detection.

Cycle-by-cycle current limiting is an inherent advantage of the peak current mode architecture. Hiccup mode current limiting provides additional protection. If an overcurrent fault occurs for more than 32 cycles, the converter stops switching for a period of time set by the soft-start capacitor. After this interval, switching operation resumes through soft-start. As shown in Figure 4, during the fault period, the converter switches in relatively short cycles, which greatly reduces the thermal stress on the MOSFETs and inductors.

The LTC7852/LTC7852-1 is a flexible, high performance, 6-phase dual output buck controller designed to provide high efficiency and highly reliable power via DrMOS, power modules, or external gate drivers and MOSFETs. Features include: sub-mΩ DCR sensing (LTC7852), selectable phase configuration, 0.5 V reference with ±0.5% total regulation accuracy, differential output sensing, 250 kHz to 1.25 MHz switching frequency range, and hiccup mode current limit protection.

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