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HC5549CMZ Datasheet(PDF) 11 Page - Intersil Corporation |
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HC5549CMZ Datasheet(HTML) 11 Page - Intersil Corporation |
11 / 13 page 11 FN4539.3 shutdown in the presence of a persistent thermal alarm. Switching between high and low battery will have no effect during power denial. Functionality During power denial, both the Tip and Ring amplifiers are disabled, representing high impedances. The voltages at both outputs are near ground. Thermal Shutdown In the event the safe die temperature is exceeded, the ALM output will go low and DET will go high and the part will automatically shut down. When the device cools, ALM will go high and DET will reflect the loop status. If the thermal fault persists, ALM will go low again and the part will shutdown. Programming power denial will permanently shutdown the device and stop the self cooling cycling. Battery Switching Overview The integrated battery switch selects between the high battery (VBH) and low battery (VBL). The battery switch is controlled with the logic input BSEL. When BSEL is a logic high, the high battery is selected and when a logic low, the low battery is selected. All operating modes of the device will operate from high or low battery except forward loop back. Functionality The logic control is independent of the operating mode decode. Independent logic control provides the most flexibility and will support all application configurations. When changing device operating states, battery switching should occur simultaneously with or prior to changing the operating mode. In most cases, this will minimize overall power dissipation and prevent glitches on the DET output. The only external component required to support the battery switch is a diode in series with the VBH supply lead. In the event that high battery is removed, the diode allows the device to transition to low battery operation. Low Battery Operation All off hook operating conditions and ringing should use the low battery. The prime benefit will be reduced power dissipation. The typical low battery for the device is -24V. However this may be increased to support longer loop lengths or high loop current requirements. Standby conditions may also operate from the low battery if MTU compliance is not required, further reducing standby power dissipation. High Battery Operation The high battery should be used for standby conditions which must provide MTU compliance. During standby operation the power consumption is typically 40 mW with - 48V battery. If standby requirements do not require high battery operation, then a lower battery will result in lower standby power. Uncommitted Switch Overview The uncommitted switch is a three terminal device designed for flexibility. The independent logic control input, SWC, allows switch operation regardless of device operating mode. The switch is activated by a logic low. The positive and negative terminals of the device are labeled SW+ and SW- respectively. Relay Driver The uncommitted switch may be used as a relay driver by connecting SW+ to the relay coil and SW- to ground. The switch is designed to have a maximum on voltage of 0.6V with a load current of 45mA. Since the device provides the ringing waveform, the relay functions which may be supported include subscriber disconnect, test access or line interface bypass. An external snubber diode is not required when using the uncommitted switch as a relay driver. Test Load The switch may be used to connect test loads across Tip and Ring. The test loads can provide external test termination for the device. Proper connection of the uncommitted switch to Tip and Ring is shown below. The diode in series with the test load blocks current from flowing through the uncommitted switch when the polarity of the Tip and Ring terminals are reversed. In addition to the reverse active state, the polarity of Tip and Ring are reversed for half of the ringing cycle. With independent logic control and the blocking diode, the uncommitted switch may be continuously connected to the Tip and Ring terminals. FIGURE 9. EXTERNAL RELAY SWITCHING RELAY SW+ SW- SWC +5V FIGURE 10. TEST LOAD SWITCHING RING TIP TEST LOAD SW+ SW- SWC HC5549 |
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