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ISL83220E Datasheet(PDF) 6 Page - Intersil Corporation |
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ISL83220E Datasheet(HTML) 6 Page - Intersil Corporation |
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6 / 11 page 
6 Power Supply Decoupling In most circumstances a 0.1 µF bypass capacitor is adequate. In applications that are particularly sensitive to power supply noise, decouple VCC to ground with a capacitor of the same value as the charge-pump capacitor C1. Connect the bypass capacitor as close as possible to the IC. Transmitter Output when Exiting Powerdown Figure 3 shows the response of the transmitter output when exiting powerdown mode. As it activates, the transmitter output properly goes to RS-232 levels, with no glitching, ringing, nor undesirable transients. The transmitter is loaded with 3k Ω in parallel with 2500pF. Note that the transmitter enables only when the magnitude of the supplies exceed approximately 3V. High Data Rates The ISL83220E maintains the RS-232 ±5V minimum transmitter output voltages even at high data rates. Figure 4 details a transmitter loopback test circuit, and Figure 5 illustrates the loopback test result at 120kbps. For this test, the transmitter is driving an RS-232 load in parallel with 1000pF, at 120kbps. Figure 6 shows the loopback results for the transmitter driving 1000pF and an RS-232 load at 250kbps. TIME (20 µs/DIV.) 2V/DIV. 5V/DIV. VCC = +3.3V SHDN FIGURE 3. TRANSMITTER OUTPUT WHEN EXITING POWERDOWN C1 - C4 = 0.1 µF TIN = LOW TIN = HIGH FIGURE 4. TRANSMITTER LOOPBACK TEST CIRCUIT FIGURE 5. LOOPBACK TEST AT 120kbps FIGURE 6. LOOPBACK TEST AT 250kbps ISL83220E VCC C1 C2 C4 C3 + + + + 1000pF V+ V- 5k TIN ROUT C1+ C1- C2+ C2- RIN TOUT + VCC 0.1 µF VCC EN SHDN T1IN T1OUT R1OUT 5 µs/DIV. VCC = +3.3V 5V/DIV. C1 - C4 = 0.1 µF T1IN T1OUT R1OUT 2 µs/DIV. 5V/DIV. VCC = +3.3V C1 - C4 = 0.1 µF ISL83220E |
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