1 Introduction

In real life, we often have such a scenario, when we connect the computer through the USB or HDMI interface to connect external devices, hard disks or monitors, we do not cut off the power supply of the PC, the external device is directly unplugged or plugged in, which is called hot-swap with power for this type of use scenario. Hot-swap allows users to remove and replace damaged hard drives, power supplies, or boards without shutting down the system or cutting off the power supply, thereby improving the system's timely disaster recovery ability, scalability, and flexibility. However, in the process of hot-swap, transient peak current and voltage occurrence is likely, if not protected, this causes the rear circuit to be damaged by the impact of transient high power. As shown in Figure 1-1, this is a typical application scenario for hot-swappable protection chips.

Because the ultrasonic equipment needs to select different probes according to different detection objects, there are hot-swap scenarios, in this application, to maintain the stability and reliability of the entire ultrasonic system in the application process, hot-swap protection chips are necessary. LM5067 is a negative voltage hot-swap protection chip launched by TI in 2020. The voltage operating range of LM5067 is -9V to -80V, while the negative voltage range of conventional ultrasonic emission systems is typically -9V to -64V. In terms of specifications, LM5067 meets the current application scenario. The internal block diagram of the L M5067 is shown in Figure 1-2, which can set the UVLO (Undervoltage lockout) and OVLO (Overvoltage lockout) to protect the post stage circuit. The specification of the LM5067 indicates the absolute maximum voltage value of the UVLO pin can not exceed VEE+17V. If exceeded, permanent damage can occur.

In a practical application, the system needs to have a dynamic change in the operating voltage, ranging from -9V to -64V. The LM5067 can be set with the voltage thresholds of UVLO and OVLO using the external resistor divider ratio as shown in Figure 1-3. UVLO pin voltage can be expressed as Equation 1.

When VCC = 0V, VEE = -9V, the resistor-to-voltage ratio must be at least 9:2.5 to meet the voltage of the UVLO pin minimum voltage greater than 2.5V, according to the calculation, when VCC=0V, VEE=-64V, the voltage of the UVLO pin can reach 17.7V, which is beyond the normal voltage working range of the chip. To solve this problem, we can change the voltage of the UVLO pin through the external circuit.