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ICL3207ECA Datasheet(PDF) 7 Page - Intersil Corporation |
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ICL3207ECA Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 12 page 7 This automatic powerdown feature provides additional system power savings without changes to the existing operating system or hardware. Utilizing power management circuitry, to power down the rest of the communication circuitry (e.g., the UART) when the ICL3217E powers down, produces even greater power savings. Connecting a transition detector to the V- pin (see Figure 3) is an easy way for the power management logic to determine when the ICL3217E enters and exits powerdown. Capacitor Selection The charge pumps require 0.1 µF, or greater, capacitors for 3.3V operation. With 0.1 µF capacitors, five percent tolerance supplies (e.g., 3.14V minimum) deliver greater than ±5V transmitter swings at full data rate, while ten percent tolerance supplies (e.g., 2.97V minimum) deliver ±4.95V transmitter swings. If greater than ±5V transmitter swings are required with a 10% tolerance 3.3V supply, 0.22 µF capacitors are recommended (see Table 3). Existing 5V applications typically utilize either 0.1 µF or 1µF capacitors, and the ICL32X7E works well with either value. New 5V designs should use 0.22 µF capacitors for the best results. 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 two) 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. Transmitter Outputs when Exiting Powerdown Figure 6 shows the response of two ICL3217E 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. . FIGURE 4. DEFINITION OF VALID RS-232 RECEIVER LEVELS 0.3V -0.3V -2.7V 2.7V INVALID LEVEL - POWERDOWN OCCURS AFTER 30 µs VALID RS-232 LEVEL - ICL3217E IS ACTIVE VALID RS-232 LEVEL - ICL3217E IS ACTIVE INDETERMINATE - POWERDOWN MAY OR MAY NOT OCCUR INDETERMINATE - POWERDOWN MAY OR MAY NOT OCCUR RECEIVER INPUTS TRANSMITTER OUTPUTS V+ VCC 0 V- INVALID REGION } FIGURE 5. AUTOMATIC POWERDOWN TIMING DIAGRAM AUTOPWDN PWR UP (tWU) TABLE 3. REQUIRED CAPACITOR VALUES VCC (V) C1 (µF) C2, C3, C4 (µF) 3.15 to 3.6 0.1 0.1 3.0 to 3.6 0.22 0.22 4.5 to 5.5 0.1 to 1.0 0.1 to 1.0 3.0 to 5.5 0.22 0.22 TIME (20 µs/DIV.) T1 T2 2V/DIV 5V/DIV VCC = +3.3V C1 - C4 = 0.1 µF RXIN FIGURE 6. TRANSMITTER OUTPUTS WHEN EXITING POWERDOWN (ICL3217E ONLY) ICL3207E, ICL3217E |
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