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at which point the command register is restored to its power-up default (0x00) and the MAX13037/ MAX13038 enter scan mode. Note that SD is compati- ble with both logic and BAT voltage levels. Having SD compatible to VBAT allows the MAX13037/MAX13038 to retain the settings in the command register as well as input monitoring even when VLO is disabled, provided that SD = VBAT. Applications Information Automotive Considerations Reverse-Battery Tolerance The BATREF and IN0–IN7 inputs can withstand voltages down to -45V without damage so that reverse battery is not an issue. The BAT input should be protected with a reverse-battery diode as shown in the Typical Application Circuit. The shutdown ( SD) and REGON inputs can be controlled from a battery-level source, but should be pro- tected against reverse battery in the application. Power Dissipation Wetting currents and the LDO output current can result in overheating the MAX13037/MAX13038. At the early ther- mal warning threshold of +135°C (typ), wetting currents are disabled. This allows the LDO output to remain enabled if overheating is caused by the wetting currents. At temperatures above +170°C, the LDO is also turned off to avoid damage to the device. It is important to consider the effects of wetting currents on the power dissipated by the MAX13037/MAX13038. For example, assume all inputs are configured for a continuous wetting current of 25mA, all external switch- es have an on-resistance of 1Ω and the battery voltage is +16V. If all switches are simultaneously closed, the corresponding power dissipated due to wetting currents only is (16V - (25mA x 1Ω)) x 25mA x 8 = 3.12W, which is higher than the absolute maximum power dissipation of 2857mW at +70°C. The LDO is a second source of power dissipation. For example, if VLO = +3.3V, ILO = 100mA and VBAT = +16V, the power dissipated by the LDO is (16V - 3.3V) + (0.1) = 1.27W. Both the LDO and wetting currents should be taken into account for correct use of the MAX13037/MAX13038. ESD Protection As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electro- static discharges encountered during handling and assembly. The IN7–IN0 inputs have extra protection against static electricity. Maxim’s engineers have developed state-of-the-art structures to protect these pins against ESD of ±8kV without damage. Human Body Model The MAX13037/MAX13038 IN7–IN0 pins are charac- terized for ±8kV ESD protection using the Human Body Model. Figure 7a shows the Human Body Model, and Figure 7b shows the current waveform it gener- ates when discharged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the device through a 1.5kΩ resistor. Automotive Contact Monitor and Level Shifters with LDO Regulator 18 ______________________________________________________________________________________ CHARGE-CURRENT- LIMIT RESISTOR DISCHARGE RESISTANCE STORAGE CAPACITOR Cs 100pF RC 1M Ω RD 1500 Ω HIGH- VOLTAGE DC SOURCE DEVICE UNDER TEST Figure 7a. Human Body ESD Test Model IP 100% 90% 36.8% tRL TIME tDL CURRENT WAVEFORM PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE) Ir 10% 0 0 AMPERES Figure 7b. Human Body Model Current Waveform |
