Achieving nano I_Q in automotive DC/DC converters

There are many always-on automotive applications such as sensors, e-call systems and zone control units where long standby time and high efficiency at light loads are very crucial. The LMQ66430-Q1 buck converter is designed to overcome these challenges, achieving >85% efficiency at 1mA loads and allowing an unloaded typical current consumption of 1.5µA at 13.5V_IN. The IC runs an impedance check at startup on the VOUT/FB pin. If no external feedback resistors are detected, the device will automatically use an internal feedback network that sets a fixed 3.3V or 5V output voltage, which helps minimize leakages through the feedback network and reduces I_Q. The LMQ66430-Q1 uses an internal low-dropout regulator (LDO) to provide power to the internal circuitry for the IC. Rather than powering the LDO with input voltage and taking the efficiency hit, the LMQ66430-Q1 leverages the same voltage from the VOUT/FB pin to power the internal LDO, which then biases all internal circuitry in order to minimize the total I_Q.

Another buck converter, the TPS62903-Q1, uses an R2D interface to set the output voltage, enabling a reduction in leakage current. The TP62903-Q1 seamlessly transitions to power-save mode as the load decreases. In this state, the IC operates in pulse-frequency modulation (PFM) mode by reducing the switching frequency to maintain high efficiency, as shown in Figure 6 under light-load conditions. This reduces the typical I_Q to 4µA.