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ICL3227E Datasheet(PDF) 11 Page - Intersil Corporation |
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ICL3227E Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 19 page  11 Ready Output (ICL3225E and ICL3227E Only) The Ready output indicates that the ICL322XE is ready to transmit. Ready switches low whenever the device enters powerdown, and switches back high during power-up when V- reaches -4V or lower. Capacitor Selection The charge pumps require 0.1 µF capacitors for 3.3V operation. For other supply voltages refer to Table 3 for capacitor values. Do not use values smaller than those listed in Table 3. Increasing the capacitor values (by a factor of 2) reduces ripple on the transmitter outputs and slightly reduces power consumption. C2, C3, and C4 can be increased without increasing C1’s value, however, do not increase C1 without also increasing C2, C3, and C4 to maintain the proper ratios (C1 to the other capacitors). When using minimum required capacitor values, make sure that capacitor values do not degrade excessively with temperature. If in doubt, use capacitors with a larger nominal value. The capacitor’s equivalent series resistance (ESR) usually rises at low temperatures and it influences the amount of ripple on V+ and V-. 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. Operation Down to 2.7V ICL32XXE transmitter outputs meet RS-562 levels (±3.7V), at full data rate, with VCC as low as 2.7V. RS-562 levels typically ensure inter operability with RS-232 devices. Transmitter Outputs when Exiting Powerdown Figure 10 shows the response of two transmitter outputs when exiting powerdown mode. As they activate, the two transmitter outputs properly go to opposite RS-232 levels, with no glitching, ringing, nor undesirable transients. Each transmitter is loaded with 3k Ω in parallel with 2500pF. Note that the transmitters enable only when the magnitude of the supplies exceed approximately 3V. Mouse Driveability The ICL3245E is specifically designed to power a serial mouse while operating from low voltage supplies. Figure 11 shows the transmitter output voltages under increasing load current. The on-chip switching regulator ensures the transmitters will supply at least ±5V during worst case conditions (15mA for paralleled V+ transmitters, 7.3mA for single V- transmitter). High Data Rates The ICL32XXE maintain the RS-232 ±5V minimum transmitter output voltages even at high data rates. Figure 12 details a transmitter loopback test circuit, and Figure 13 illustrates the loopback test result at 250kbps. For this test, all transmitters were simultaneously driving RS-232 loads in parallel with 1000pF, at 250kbps. Figure 14 shows the loopback results for a single transmitter driving 250pF and TABLE 3. REQUIRED CAPACITOR VALUES VCC (V) C1 (µF) C2, C3, C4 (µF) 3.0 to 3.6 0.1 0.1 4.5 to 5.5 0.047 0.33 3.0 to 5.5 0.1 0.47 TIME (20 µs/DIV.) T1 T2 2V/DIV 5V/DIV VCC = +3.3V FORCEOFF FIGURE 10. TRANSMITTER OUTPUTS WHEN EXITING POWERDOWN C1 - C4 = 0.1 µF 5V/DIV READY FIGURE 11. TRANSMITTER OUTPUT VOLTAGE vs LOAD CURRENT (PER TRANSMITTER, i.e., DOUBLE CURRENT AXIS FOR TOTAL VOUT+ CURRENT) LOAD CURRENT PER TRANSMITTER (mA) 02 468 10 -6 -4 -2 0 2 4 6 -5 -3 -1 1 3 5 13579 VOUT+ VOUT - VCC VOUT+ VOUT - T1 T2 T3 VCC = 3.0V ICL3245E ICL3225E, ICL3227E, ICL3245E |
Similar Part No. - ICL3227E |
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Similar Description - ICL3227E |
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