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ISL54227 Scheda tecnica(PDF) 10 Page - Intersil Corporation |
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ISL54227 Scheda tecnica(HTML) 10 Page - Intersil Corporation |
10 / 18 page ISL54227 10 FN7593.0 July 2, 2010 With a negative -5V fault voltage at both com pins, the graph in Figure 7 shows the IDD current draw for different external resistor values for supply voltages of 2.7V, 3.6V, and 5.25V. Note: 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 overstress 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. CHARGER PORT DETECTION The ISL54227 has special charger port detection circuitry that monitors the voltage at the com pins to detect when a battery charger has been connected into the USB port (see Figure 8). When the battery charger is connected into the USB connector, it shorts the COM+ and COM- pins together. The shorting of the pins is sensed by the ISL54227 IC and it pulls the COM+ and COM- lines high and as long as the OE = “0” or is tri-stated by the µP, it will drive its INT logic output “Low” to tell the power management circuitry that a battery charger is connected at the port and not a USB host transceiver. The power management circuitry will then use the USB connector VBUS line to charge the battery. ISL54227 Operation The following will discuss using the ISL54227 shown in the “Application Block Diagram” on page 8. POWER The power supply connected at the VDD pin provides the DC bias voltage required by the ISL54227 part for proper operation. The ISL54227 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. LOGIC CONTROL The state of the ISL54227 device is determined by the voltage at the OE pin, LP pin, and the signal voltage at the COM pins. Refer to “Truth Table” on page 2. FIGURE 6. VDD SERIES RESISTOR TO LIMIT IDD CURRENT DURING NEGATIVE OVP AND FOR ENHANCED ESD AND LATCH-UP IMMUNITY FIGURE 7. NEGATIVE OVP IDD CURRRENT vs RESISTOR VALUE vs VSUPPLY D+ 100Ω TO 1kΩ COM+ COM- VSUPPLY GND C PROTECTION RESISTOR OVP LOGIC D- IDD VDD -5V FAULT VOLTAGE ALM INT LOW TO INDICATE OVP OE LP 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 FIGURE 8. CHARGER PORT DETECTION OE D+ COM+ COM- VSUPPLY GND C LOGIC D- LP VDD ALM INT USB TRANCEIVER BATTERY CHARGER µP 200Ω CHG DET POWER BATTERY CHARGER CIRCUITRY MANAGEMENT “LOW” TO INDICATE CHARGER CONNECTED OE = “0” OR TRI-STATE VBUS GND D+ D- |
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