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CA3277E датащи(PDF) 5 Page - Intersil Corporation |
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CA3277E датащи(HTML) 5 Page - Intersil Corporation |
5 / 8 page 7-43 CA3277 FIGURE 2. CURRENT MULTIPLIER DRIVING A REMOTE CA3277 DATA COMPARATOR Data Comparator - The Data Comparator provides a means of translating serial data from a high to low voltage. The DATA IN terminal of the Data Comparator is biased to receive signal input that is source referenced to the BATT supply voltage level. In normal use the signal input would be supplied from a remote Current Multiplier having a resistor load tied to the BATT voltage supply. The DATA OUT output from the Data Comparator is CMOS compatible 5V non- inverting logic data referenced to GND. The switching threshold at the DATA IN input is bias stabilized by the band- gap voltage and is typically at (VBATT - 2.9V). The Data Comparator is in a high state when DATA IN input is at the BATT voltage level and is in a low state when DATA IN is at (VBATT - 5V). The output stage of the Data Comparator is internally supply biased from the Switched 5V Regulator output to provide a high state of 5V and a low state of 0V (GND). The DATA OUT terminal can typically sink 1.2mA in a low state or source 50 µA in a high state. In system applications the Data Comparator is used to translate remote data at high voltage down to 5V logic levels. The Current Multiplier is used to reverse the process by translating 5V logic data back to the BATT voltage level when sending data back to the remote system. The Data Comparator and Current Multiplier are level matched for remote communication between microcontroller systems using the common BATT power supply voltage of the CA3277. The current driven serial data from the Current Multiplier is sent to a remote system by translating the signal up to the BATT voltage level, or an external power supply level that is compatible with the remote device. The Data Comparator of the remote system receives the data, interfaces to its microcontroller and responds with signal drive from its Current Multiplier to translate the signal back to the host. For best noise immunity the transmission in each direction should be over a twisted pair or shielded line. As such, two microcontrollers, each with the interface protection of a CA3277, can provide intelligent master/slave system communications under adverse environmental conditions. 510 Ω 250 Ω CA3277 REMOTE SYSTEM + - DATA COMP. BATT DI CA3277 INTERNALLY CONNECTED TO OUT1 (+5V) Q100 Q99 5X GAIN ICIN Q103 Q102 C3 10pF Q101 CUR IN 10 20X GAIN 9 CUR OUT GND 4, 5 AND 12, 13 Ignition Comparator - While the Ignition Comparator is pro- vided as an essential part of the start-up control in automo- tive systems, this circuit function may be used as an independent switching comparator. It is important to note that the thermal shutdown feature on the chip is dis- abled when the IGN IN input is low. Disabling of the on- chip thermal protection is done to satisfy the requirement of low idle current when the system is in a standby condition. The non-inverting IGN IN input has a switching threshold of typically 6V with 200mV of hysteresis and is switched with logic levels reference to GND as the low state and BATT as the high state. The IGN OUT output is 5V CMOS compatible logic, equivalent to the Data Comparator output stage, but is internally supply biased from the Standby 5V Regulator. As such, the high state is level referenced to OUT1. The IGN OUT output terminal can typically sink 1.2mA in a low state or source 70 µA in a high state. Enable - A CMOS or TTL high at the ENABLE input switches the regulated 5V/Switched Output ON at OUT2. The ENABLE input has an internal pull-down of typically 50 µA to ensure that OUT2 is OFF when the ENABLE input is not connected. The input threshold level for switching is the bandgap voltage reference of 1.2V. When the ENABLE input is low, all drive current to the output pass transistor is cutoff and OUT2 voltage drops to ground level. The ENABLE input is normally switched from the interfacing microcontrol- ler but may be activated from a remote source. Reset - The purpose of the Low Voltage Reset function is to flag a low voltage condition at OUT1. When the RESET out- put, pin 8 switches low, the voltage level at OUT1 has dropped below the regulation level. The CRST and RESET are high when OUT1 is at 5V. When OUT1 drops to less than 4.2V (typical), the CRST Capacitor at pin 7 is internally discharged, causing the RESET pin to change from a high to a low state, outputting a negative going pulse. The RESET output is an NPN open collector driver requiring an external load resistor, normally connected to OUT1. The RESET output flag may be sent to a microcontroller to initiate a power-down sequence. For any condition that causes OUT1 to drop below the reset threshold, such as undesired transients, the RESET output is switched low for a delay period, tRST determined by the value of the external capacitor, CRST at CRST terminal. For a value of 0.47µF the delay period is typically 141ms. This correlates to approxi- mately 10µA of charging current sourced from the CRST terminal to charge CRST. Regulation - The regulated output stages of the CA3277 have similar circuits, each having an error amplifier to compare the output voltage to the bandgap reference voltage. The circuit of the 5V/Switched regulator is shown in Figure 3. By feedback, the output voltage is differentially compared to the bandgap reference voltage. The error signal is then amplified to drive a PNP pass transistor and maintain a stable 5V output with both line and load regulation over the full operating temperature range. Except for the ENABLE control of OUT2, the OUT1 drive circuit is similar to the OUT2 circuit. |
Аналогичный номер детали - CA3277E |
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Аналогичное описание - CA3277E |
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