Design of Protection Circuit for Internal ESD Diode of MAX2140

When a MAX2140 SDARS receiver is hot-plugged (plugged in or disconnected), it may invalidate its internal electrostatic discharge (ESD) protection diode, which is not the standard operation of the device. However, this situation can occur in many applications, especially in the automotive industry, where hot-plug operations are often performed. This paper analyses the possible causes of ESD diode failure due to hot-plug operation, and helps to design a reasonable circuit to prevent diode failure.

Summary

Non-standard operation of the MAX2140 SDARS receiver is sometimes required for assembly, testing, and troubleshooting. One example is the hot-plug operation, which connects or disconnects the device directly from the circuit without switching off the power supply. Hot-plug operations are particularly common in automotive electronics because of the modular design of components, the distance between modules, and the need for multiple systems to work simultaneously, modules often need to be reconnected.

How Hot Plug Operation Causes Diode Failure

Hot-plug operations can cause transient changes, including higher voltage, surge current, ringing, and polarity inversion. Behind these transient processes are physical phenomena such as energy exchange, limited charging/discharging time and self-excitation.
Figure 1 shows a hot-plug operation for MAX2140.

During hot-plug operation, the cable connector produces a voltage drop (as shown by the red arrow in the figure). At the same time, the bypass capacitance inside the antenna module is in short-circuit state. This results in a higher potential in the MAX2140 electrical ground than in the antenna module electrical ground. The internal ESD diode of MAX2140 is connected to the ground pin 16 of the IC, so this ground potential difference will generate a short positive voltage on the diode. The spike in the forward voltage may exceed the device rating, which is called electrical overload (EOS). The forward voltage of the diode is specified to be -0.3V to +4.3V (VCC_xx to GND, VINANT to GND, AGCPWM to GND, VOUTANT to GND). The design simulation shows that -1.3V, 72 mA current allows short time operation.

Design to Prevent Failure of ESD Diode

The way to prevent EOS varies depending on the application. Some general design improvements are recommended here:

Avoid using too many reactances, such as energy storage elements, bypass capacitance, RF noise suppression inductance, long connection lines, etc.

Make surge current bypass: Provide a shorter direct grounding path for each module; Increase the external diode so that it is parallel to the internal diode; Connect the diode across a large coil.

Sequential power supply: turn on the power supply sequentially; Recommend programmable latency for internal users (Maxim has many power sequencing products).

The following design example (Figure 2) shows the MAX2140 with a local loop, and the added Schottky diode can bypass the surge current.

Specific design improvement measures are:

The cable between the MAX2140 receiver and the antenna module has only 0.5 resistance and no inductance.
Antenna module has a 100 μ F's bypass capacitance.
The 5V power supply for the antenna module is provided by the MAX2140 receiver.
Readers may ask, in the first 40 μ S What is the voltage drop of the current through the capacitor and the cable during the transient process. These values can be derived from the following expressions:

This example has a voltage of 6.25V at a current of 12.5A, which far exceeds the transient indices allowed by the internal ESD diode. Adding a Schottky diode can bypass most surge currents in the transient process. A Schottky diode suitable for pulse application can be selected. Based on the design of Figure 2, when the surge current is reduced to an acceptable range with an appropriate capacitance, a short cable can significantly reduce the impedance and voltage drop.

conclusion

Problems with non-standard use of devices, such as hot-plug operation of MAX2140 receivers, need to be addressed in appropriate ways. In order to successfully implement non-standard use of devices, the product must be carefully designed and tested with Maxim support and consent.