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ISL5571A 数据表(PDF) 9 Page - Intersil Corporation |
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ISL5571A 数据表(HTML) 9 Page - Intersil Corporation |
9 / 12 page 9 TSD Pin The TSD pin (pin 8) can be used as a logic level input or output. Reference Table 9 for logic state table. The TSD pin overrides all other logic pins. As an input, if this pin is driven low, either by external logic applied to it or by the internal thermal shutdown circuitry, the ISL5571A device will enter the All OFF state. In the All OFF state all switches of the ISL5571A are open (off). As an output, it is capable of driving a TTL input (2.8V at 200 µA). The TSD pin will read +5V when the device is in normal operating mode and 0V when the device is in thermal shutdown. This pin can be monitored on an oscilloscope to determine if the ISL5571A device has enter thermal shutdown. (Thermal Shutdown is described in the Auxiliary Functions and Features section below.) Connecting the TSD pin to 5V will have no effect on the performance of the ISL5571A device and will not disable the thermal shutdown circuitry. Auxiliary Functions and Features In addition to the ISL5571A main function of momentarily connecting and disconnecting an external ring generator to ring the phone, the ISL5571A device also provides surge and power-cross protection to the SLIC and CODEC. This fault protection is provided by a combination of current- limiting circuitry, a thermal shutdown mechanism and an over-voltage clamping circuit. Another feature the device offers is a VBAT fault detection circuit. The following describes each in detail. Current Limiting The Line Break switches (SW1 and SW2) and the Ring Return switch (SW3) are all current-limited. These switches have a DC current limiting response and a dynamic current limiting response which were built into the device to provide protection during lightning and power-cross faults. Each of these current limiting responses are explained below. DC CURRENT LIMITING RESPONSE The ON state V-I Graph for SW1, SW2, and SW3 is shown in Figure 3. It represents the DC current limiting response of the switches. The graph shows that over a certain range of positive and negative voltages, the current and voltage relationship is linear and behaves according to Ohms law (V = IR). Note: At around ±1.5V an inflection point occurs decreasing the on resistance by 2/3. The on resistance specified in the data sheet is measured in the region prior to the inflection point (between ±1.5V). When current through the switch reaches the current limit of the switch, the current is clamped and held at a constant value. The switch then operates as a constant current source. Increasing the voltage beyond this point will not change the value of the current. CURRENT LIMITING +I -I ILIMIT CURRENT LIMITING rON ILIMIT +V FIGURE 3. ON STATE V-I GRAPH OF SW1, SW2 AND SW3 rON +1.5 -1.5 2/3 rON 2/3 rON -V +I -I +V FIGURE 4. EFFECT OF TEMPERATURE ON DC CURRENT LIMIT T2 T1 T1 T2 > T1 T2 -V +I TIME 0 FIGURE 5. DYNAMIC CURRENT LIMIT RESPONSE 2A 0.5 µs ISL5571A |
类似零件编号 - ISL5571A |
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类似说明 - ISL5571A |
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