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MAX4551ESE Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX4551ESE Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 16 page ±15kV ESD-Protected, Quad, Low-Voltage, SPST Analog Switches 8 _______________________________________________________________________________________ Applications Information MAX4551/MAX4552/MAX4553 ±15kV ESD Protection The MAX4551/MAX4552/MAX4553 are ±15kV ESD-pro- tected according to IEC 1000-4-2 at their NC/NO pins. To accomplish this, bidirectional SCRs are included on- chip between these pins and the GND pin. In normal operation, these SCRs are off and have negligible effect on the performance of the switches. When there is an ESD strike at these pins, however, the voltages at these pins go Beyond-the-Rails™ and cause the corre- sponding SCR(s) to turn on in a few nanoseconds and bypass the surge safely to ground. This method is superior to using diode clamps to the supplies because unless the supplies are very carefully decoupled through low ESR capacitors, the ESD current through the diode clamp could cause a significant spike in the supplies. This may damage or compromise the reliabili- ty of any other chip powered by those same supplies. In the MAX4551/MAX4552/MAX4553, there are diodes to the supplies in addition to the SCRs at the NC/NO pins, but there is a resistance in series with these diodes to limit the current into the supplies during an ESD strike. The diodes are present to protect these pins from overvoltages that are not as a result of ESD strikes like those that may occur due to improper power-supply sequencing. Once the SCR turns on because of an ESD strike, it continues to be on until the current through it falls below its “holding current.” The holding current is typi- cally 110mA in the positive direction (current flowing into the NC/NO pin) and 95mA in the negative direction at room temperature (see SCR Holding Current vs. Temperature in the Typical Operating Characteristics). The system should be designed such that any sources connected to these pins are current limited to a value below these to make sure the SCR turns off when the ESD event gets over to resume normal operation. Also, keep in mind that the holding current varies significant- ly with temperature. At +85°C, which represents the worst case, the holding currents drop to 70mA and 65mA in the positive and negative directions respec- tively. Since these are typical numbers, to get guaran- teed turn-off of the SCRs under all conditions, the sources connected to these pins should be current lim- ited to not more than half these values. When the SCR is latched, the voltage across it is about ±3V, depend- ing on the polarity of the pin current. The supply volt- ages do not affect the holding currents appreciably. The sources connected to the COM side of the switches do not need to be current limited since the switches are made to turn off internally when the corresponding SCR(s) get latched. Even though most of the ESD current flows to GND through the SCRs, a small portion of it goes into the supplies. Therefore, it is a good idea to bypass the supply pins with 100nF capacitors directly to the ground plane. ESD protection can be tested in various ways. Trans- mitter outputs and receiver inputs are characterized for protection to the following: • ±15kV using the Human Body Model • ±8kV using the Contact Discharge method speci- fied in IEC 1000-4-2 (formerly IEC 801-2) • ±15kV using the Air-Gap Discharge method speci- fied in IEC 1000-4-2 (formerly IEC 801-2). ESD Test Conditions Contact Maxim for a reliability report that documents test setup, methodology, and results. Human Body Model Figure 8 shows the Human Body Model, and Figure 9 shows the current waveform it generates when dis- charged into a low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of inter- est, which is then discharged into the test device through a 1.5k Ω resistor. IEC 1000-4-2 The IEC 1000-4-2 standard covers ESD testing and performance of finished equipment; it does not specifi- cally refer to integrated circuits. The MAX4551/MAX4552/ MAX4553 enable the design of equipment that meets Level 4 (the highest level) of IEC 1000-4-2, without additional ESD protection components. The major difference between tests done using the Human Body Model and IEC 1000-4-2 is higher peak current in IEC 1000-4-2. Because series resistance is lower in the IEC 1000-4-2 ESD test model (Figure 10), the ESD withstand voltage measured to this standard is generally lower than that measured using the Human Body Model. Figure 11 shows the current waveform for the ±8kV IEC 1000-4-2 Level 4 ESD Contact Discharge test. The Air-Gap test involves approaching the device with a charged probe. The Contact Discharge method connects the probe to the device before the probe is energized. Beyond-the-Rails is a trademark of Maxim Integrated Products. |
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