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LTC4557 Datasheet(PDF) 9 Page - Linear Technology |
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LTC4557 Datasheet(HTML) 9 Page - Linear Technology |
9 / 12 page 9 LTC4557 4557f APPLICATIO S I FOR ATIO 10kV ESD Protection All smart card pins (CLKA,B, RSTA,B, I/OA,B, VCCA,B and GND) can withstand over 10kV of human body model ESD in-situ. In order to ensure proper ESD protection, careful board layout is required. The GND pad should be tied directly to a ground plane. The VCCA,Bcapacitors should be located very close to the VCCA,B pins and tied immediately to the ground plane. Capacitor Selection A total of four capacitors are required for proper bypassing of the LTC4557. An input bypass capacitor is required at VBATT and DVCC. Output bypass capacitors are required on each of the smart card VCCA,B pins. Due to their extremely low equivalent series resistance (ESR), only multilayer ceramic chip capacitors should be used to ensure proper stability and ESD protection. There are several types of ceramic capacitors available each having considerably different characteristics. For example, X7R/X5R ceramic capacitors have excellent volt- age and temperature stability but relatively low packing density. Y5V ceramic capacitors have apparently higher packing density but poor performance over their rated voltage or temperature ranges. Under certain voltage and temperature conditions Y5V and X7R/X5R ceramic capacitors can be compared directly by case size rather than specified value for a desired minimum capacitance. The VCCA,B outputs should be bypassed to GND with a 1µF capacitor. VBATT should be bypassed with a 0.1µF ceramic capacitor. Capacitors should be placed as close to the LTC4557 as possible for improved ESD tolerance. The following capacitors are recommended for use with the LTC4557: TYPE VALUE CASE SIZE MURATA PART NUMBER CVCC, X5R 1 µF 0603 GRM188R60J105KA01 VCCA/B CDVCC, X5R 0.1 µF 0402 GRM155R61A104KA01 DVCC Compliance Testing Inductance due to long leads on type approval equipment can cause ringing and overshoot that leads to testing problems. Small amounts of capacitance and damping resistors can be included in the application without com- promising the normal electrical performance of the LTC4557 or smart card system. Generally a 100 Ω resistor and a 20pF capacitor will accomplish this as shown in Figure 2. 100 Ω 100 Ω 100 Ω 20pF 20pF 20pF 0.1 µF 1 µF 4557 F02 VCCX CLKX LTC4557 RSTX I/OX SMART CARD SOCKET C1 C3 C2 C7 C5 Figure 2. Additional Components for Improved Compliance Testing |
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