In harsh automotive environments, external resistors limit I_Q at the system level. Given requirements to prevent leakage, resistors are usually limited to lower than 100 kΩ. But you don’t have to abandon your low-I_Q and I_SHDN ambitions. An external feedback divider monitoring 12 V will result in an I_Q in the >100 µA range. You could use an internal feedback divider with higher resistance to reduce the divider current, but at the cost of losing programmability.

The LM5123-Q1 wide V_IN boost controller achieves lower I_Q by swapping the classical external feedback resistor and internal low-voltage reference, thus enabling low-value resistors at little expense. With this innovative placement of the voltage reference and feedback resistor, the 300-µA I_Q in the previous example drops by more than a factor of 20, see Figure 22.

Similar to the LM5123-Q1, the LMR43610/20 36-V, 1-A/2-A buck converter utilizes a novel approach to minimizing I_Q by integrating the feedback network. The LMR43610/20 runs an impedance check at startup on the VOUT/FB pin, which senses the presence of an external feedback network that engineers can employ to leverage the adjustable output voltage feature. If no external feedback resistors are detected, the device will automatically utilize the integrated feedback network that sets a fixed 3.3-V or 5-V output voltage. This minimizes leakages through the feedback network and lowers I_Q

Many switch-mode power devices like LMR43610/20 use an internal LDO to provide power to the internal circuitry for the IC. Low-voltage applications will typically supply this internal LDO directly from the input voltage. However, this method of powering the internal LDO poses a unique challenge in designs that operate across wide input voltage as the power loss from the LDO is directly proportional to input voltage.

To address it, rather than drawing power from the input, the LMR43610/20 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_VIN. This decreases the internal LDO current by a factor of V_OUT / (V_IN * η1). These features, paired with the methods discussed throughout this paper, enable the LMR43610/20 to have best-in-class I_Q of <3 μA (max.) at 150°C T_J, and light-load efficiency of almost 90% at 1 mA for nominal 12-V_IN, 3.3-V_OUT, 2.2-MHz conversions.