The LMQ644xx is a wide-input, synchronous, buck DC/DC converter for high-current single or dual outputs. The device uses an interleaved, stackable, current-mode control architecture for easy loop compensation, fast transient response, excellent load and line regulation, and accurate current sharing stackable up to six phases for higher output currents up to 36 A.

A high-side switch minimum on-time of 55 ns allows large step-down ratios, enabling the direct conversion from 12-V, 24-V, or automotive inputs to low-voltage rails for reduced system complexity and design cost. The LMQ644xx supports input voltage dips as low as 3 V, at nearly 100% duty cycle. If the minimum on-time or minimum off-time does not support the desired conversion ratio, the frequency is reduced. This action automatically allows regulation to be maintained during load dump and with very low dropout during cranking.

Power the bias of LMQ644xx from the output of the converter for lower input quiescent current and power loss. Achieving 9-μA no-load quiescent current in dual output configuration to extend operating run-time in battery-powered systems.

The LMQ644xx has been designed for low EMI. The device includes the following:

• Reduction of noise at the fundamental switching frequency through interleaving

  • To reduce input capacitor ripple current and EMI filter size, the device can be configured to operate in a stack of either two, four or six phases with corresponding phase shift interleave operation based on the number of phases. For example, in a 4 phase setup, a 90° out-of-phase clock output setup works well for cascaded, multi-channel, or multi-phase power stages. Phase relationship is maintained in light load operation for low output voltage ripple.
• Pin-enabled dual random spread spectrum (DRSS)
  • Dual Random Spread Spectrum (DRSS) frequency hopping is set to ±10% (typical), drastically reducing peak emissions through a combination of triangular and pseudorandom modulation.
• Symmetrical V_IN pinout for low input inductance
• Operation over a frequency range above and below AM radio band
  • Resistor-adjustable switching frequency adjustable from 100 kHz to 2.2 MHz can be synchronized to an external clock source to eliminate beat frequencies in noise-sensitive applications.
• Internal input capacitors for EMI reduction
  • Each phase has two 22-nF input bypass capacitors configured in series for improved system reliability.

Together, these features can eliminate shielding and other expensive EMI mitigation measures.

The device also includes the following features:

• Internal fixed soft start or adjustable soft start using an external capacitor with monotonic start-up into prebiased loads
• Open-drain Power-Good flags with built-in delayed release for fault reporting and output monitoring
• Independent enable inputs
• Integrated VCC bias supply regulator
• Hiccup-mode overload protection
• Thermal shutdown protection with automatic recovery

The LMQ644xx comes in a 5-mm × 4-mm Enhanced HotRod QFN 24-pin package with enlarged corner terminals for improved BLR and wettable flanks, allowing for optical inspection and allowing use in reliability-conscious environments