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MAX3381EEUP Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX3381EEUP Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 14 page +2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers with ±15kV ESD-Protected I/O and Logic Pins ______________________________________________________________________________________ 11 to IEC 1000-4-2 are generally lower than that measured using the Human Body Model. Figure 6a shows the IEC 1000-4-2 model, and Figure 6b 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 con- nects the probe to the device before the probe is ener- gized. Machine Model The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resis- tance. Its objective is to emulate the stress caused by contact that occurs with handling and assembly during manufacturing. All pins require this protection during manufacturing, not just RS-232 inputs and outputs. Therefore, after PC board assembly, the Machine Model is less relevant to I/O ports. Applications Information Capacitor Selection The capacitor type used for C1–C4 is not critical for proper operation. Polarized or nonpolarized capacitors can be used. The charge pump requires 0.1µF capaci- tors for +3.3V operation. For other supply voltages, see Table 2 for required capacitor values. Do not use val- ues smaller than those listed in Table 2. Increasing the capacitor values (e.g., by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. C2, C3, and C4 can be increased without changing C1’s value. However, do not increase C1 without also increasing the values of C2, C3, C4, and C5 to maintain the proper ratios (C1 to the other capac- itors). When using the minimum required capacitor values, make sure the capacitor value does not degrade excessively with temperature. If in doubt, use capaci- tors with a large nominal value. The capacitor’s equiva- lent series resistance (ESR) usually rises at low temperatures and influences the amount of ripple on V+ and V-. Power-Supply Decoupling In most circumstances, connect a 0.1µF capacitor from VCC to GND. This capacitor is for noise reduction. If the MAX3380E/MAX3381E are used in a data cable appli- cation, add a 47µF capacitor from VCC to ground. The 47µF capacitor is used to ensure that the current need- ed during power-up is supplied to the device. In appli- cations that are sensitive to power-supply noise, decouple VCC to ground with a capacitor of the same value as charge-pump capacitor C1. Connect bypass capacitors as close to the IC as possible. Transmitter Outputs when Recovering from Shutdown Figure 7 shows two transmitter outputs when exiting shutdown mode. As they become active, the two trans- mitter outputs are shown going to opposite RS-232 lev- els (one transmitter input is high, the other is low). Each transmitter is loaded with 3k Ω in parallel with 1000pF. The transmitter outputs display no ringing or undesir- able transients as they come out of shutdown. Note that the transmitters are enabled only when the magnitude of V- exceeds approximately 3V. High Data Rates The MAX3380E/MAX3381E maintain the RS-232 ±5.0V minimum transmitter output voltage even at high data rates. Figure 8 shows a transmitter loopback test cir- cuit. Figure 9 shows a loopback test result for the MAX3380E at 460kbps with true RS-232 output voltage levels (VCC = +4.2V). Figure 10 shows the same test with RS-232-compatible levels (VCC = +2.5V). With data rates as high as 460kbps, the MAX3380E is com- patible with 2.5-Generation GSM standards. VCC (V) C1, C5 (µF) C2, C3, C4 (µF) +2.35 to +3.6 0.1 0.1 +4.5 to +5.5 0.047 0.33 +2.35 to +5.5 0.22 1 Table 2. Minimum Required Capacitor Values VCC = 3.3V, C1–C4 = 0.1 µF, CLOAD = 1000pF 4 µs/div 5V/div 2V/div T2OUT T1OUT FORCEON = FORCEOFF 5V 6V 6V 0 0 Figure 7. Transmitter Outputs when Recovering from Shutdown or Powering Up |
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