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ISL54225IRTZ-T Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL54225IRTZ-T Datasheet(HTML) 10 Page - Intersil Corporation |
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10 / 18 page  10 FN7627.0 July 2, 2010 The HS1 channel switches are active (turned ON) whenever the SEL voltage is logic “0”(Low) and the OE voltage is logic “0”(Low). The HS2 channel switches are active (turned ON) whenever the SEL voltage is logic “1” (High) and the OE voltage is logic “0” (Low). OVERVOLTAGE PROTECTION (OVP) The maximum normal operating signal range for the HSx switches is from 0V to 3.6V. For normal operation, the signal voltage should not be allowed to exceed these voltage levels or go below ground by more than -0.3V. However, in the event that a positive voltage > 3.8V (typ) to 5.25V, such as the USB 5V VBUS voltage, gets shorted to one or both of the COM+ and COM- pins or a negative voltage < -0.5V (typ) to -5V gets shorted to one or both of the COM pins, the ISL54225 has OVP circuitry to detect the overvoltage condition and open the SPDT switches to prevent damage to the USB down-stream transceivers connected at the signal pins (HS1D-, HS1D+, HS2D-, HS2D+). The OVP and power-off protection circuitry allows the COM pins (D-, D+) to be driven up to 5.25V while the VDD supply voltage is in the range of 0V to 5.25V. In this condition, the part draws < 100µA of ICOMx and IDD current and causes no stress to the IC. In addition, the SPDT switches are OFF and the fault voltage is isolated from the other side of the switch. External VDD Series Resistor to Limit IDD Current during Negative OVP Condition A 100Ω to 1kΩ resistor in series with the VDD pin (see Figure 7) is required to limit the IDD current draw from the system power supply rail during a negative OVP fault event. With a negative -5V fault voltage at both COM pins, the graph in Figure 8 shows the IDD current draw for different external resistor values for supply voltages of 2.7V, 3.6V, and 5.25V. With a 500Ω resistor, the current draw is limited to around 5mA. When the negative fault voltage is removed, the IDD current will return to it’s normal operation current of 25µA to 45µA. The series resistor also provides improved ESD and latch-up immunity. During an overvoltage transient event (such as occurs during system level IEC 61000 ESD testing), substrate currents can be generated in the IC that can trigger parasitic SCR structures to turn ON, creating a low impedance path from the VDD power supply to ground. This will result in a significant amount of current flow in the IC, which can potentially create a latch-up state or permanently damage the IC. The external VDD resistor limits the current during this over-stress situation and has been found to prevent latch-up or destructive damage for many overvoltage transient events. Under normal operation, the low microamp IDD current of the IC produces an insignificant voltage drop across the series resistor resulting in no impact to switch operation or performance. ISL54225 Operation The following will discuss using the ISL54225 shown in the “Application Block Diagram” on page 9. POWER The power supply connected at the VDD pin provides the DC bias voltage required by the ISL54225 part for proper operation. The ISL54225 can be operated with a VDD voltage in the range of 2.7V to 5.25V. For lowest power consumption you should use the lowest VDD supply. A 0.01µF or 0.1µF decoupling capacitor should be connected from the VDD pin to ground to filter out any power supply noise from entering the part. The capacitor should be located as close to the VDD pin as possible. In a typical application, VDD will be in the range of 2.8V to 4.3V and will be connected to the battery or LDO of the portable media device. FIGURE 7. VDD SERIES RESISTOR TO LIMIT IDD CURRENT DURING NEGATIVE OVP AND FOR ENHANCED ESD AND LATCH-UP IMMUNITY FIGURE 8. NEGATIVE OVP IDD CURRENT vs RESISTOR VALUE vs VSUPPLY SEL D+ D- GND OVP LOGIC VDD OE HSD1+ 100Ω to 1kΩ VSUPPLY C PROTECTION RESISTOR HSD1- IDD -5V FAULT VOLTAGE HSD2+ HSD2- 0 5 10 15 20 25 100 200 300 400 500 600 700 800 900 1k RESISTOR (Ω) VCOM+ = VCOM- = -5V 2.7V 3.6V 5.25V ISL54225 |
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