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MC34161DR2 bảng dữ liệu(PDF) 7 Page - ON Semiconductor |
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MC34161DR2 bảng dữ liệu(HTML) 7 Page - ON Semiconductor |
7 / 18 page MC34161, MC33161, NCV33161 http://onsemi.com 7 FUNCTIONAL DESCRIPTION Introduction To be competitive in today’s electronic equipment market, new circuits must be designed to increase system reliability with minimal incremental cost. The circuit designer can take a significant step toward attaining these goals by implementing economical circuitry that continuously monitors critical circuit voltages and provides a fault signal in the event of an out−of−tolerance condition. The MC34161, MC33161 series are universal voltage monitors intended for use in a wide variety of voltage sensing applications. The main objectives of this series was to configure a device that can be used in as many voltage sensing applications as possible while minimizing cost. The flexibility objective is achieved by the utilization of a unique Mode Select input that is used in conjunction with traditional circuit building blocks. The cost objective is achieved by processing the device on a standard Bipolar Analog flow, and by limiting the package to eight pins. The device consists of two comparator channels each with hysteresis, a mode select input for channel programming, a pinned out reference, and two open collector outputs. Each comparator channel can be configured as either inverting or noninverting by the Mode Select input. This allows a single device to perform over, under, and window detection of positive and negative voltages. A detailed description of each section of the device is given below with the representative block diagram shown in Figure 14. Input Comparators The input comparators of each channel are identical, each having an upper threshold voltage of 1.27 V ±2.0% with 25 mV of hysteresis. The hysteresis is provided to enhance output switching by preventing oscillations as the comparator thresholds are crossed. The comparators have an input bias current of 60 nA at their threshold which approximates a 21.2 M W resistor to ground. This high impedance minimizes loading of the external voltage divider for well defined trip points. For all positive voltage sensing applications, both comparator channels are fully functional at a VCC of 2.0 V. In order to provide enhanced device ruggedness for hostile industrial environments, additional circuitry was designed into the inputs to prevent device latchup as well as to suppress electrostatic discharges (ESD). Reference The 2.54 V reference is pinned out to provide a means for the input comparators to sense negative voltages, as well as a means to program the Mode Select input for window detection applications. The reference is capable of sourcing in excess of 2.0 mA output current and has built−in short circuit protection. The output voltage has a guaranteed tolerance of ±2.4% at room temperature. The 2.54 V reference is derived by gaining up the internal 1.27 V reference by a factor of two. With a power supply voltage of 4.0 V, the 2.54 V reference is in full regulation, allowing the device to accurately sense negative voltages. Mode Select Circuit The key feature that allows this device to be flexible is the Mode Select input. This input allows the user to program each of the channels for various types of voltage sensing applications. Figure 15 shows that the Mode Select input has three defined states. These states determine whether Channel 1 and/or Channel 2 operate in the inverting or noninverting mode. The Mode Select thresholds are shown in Figure 6. The input circuitry forms a tristate switch with thresholds at 0.63 V and Vref + 0.23 V. The mode select input current is 10 mA when connected to the reference output, and 42 mA when connected to a VCC of 5.0 V, refer to Figure 7. Output Stage The output stage uses a positive feedback base boost circuit for enhanced sink saturation, while maintaining a relatively low device standby current. Figure 11 shows that the sink saturation voltage is about 0.2 V at 8.0 mA over temperature. By combining the low output saturation characteristics with low voltage comparator operation, this device is capable of sensing positive voltages at a VCC of 1.0 V. These characteristics are important in undervoltage sensing applications where the output must stay in a low state as VCC approaches ground. Figure 5 shows the Output Voltage versus Supply Voltage in an undervoltage sensing application. Note that as VCC drops below the programmed 4.5 V trip point, the output stays in a well defined active low state until VCC drops below 1.0 V. APPLICATIONS The following circuit figures illustrate the flexibility of this device. Included are voltage sensing applications for over, under, and window detectors, as well as three unique configurations. Many of the voltage detection circuits are shown with the open collector outputs of each channel connected together driving a light emitting diode (LED). This ‘ORed’ connection is shown for ease of explanation and it is only required for window detection applications. Note that many of the voltage detection circuits are shown with a dashed line output connection. This connection gives the inverse function of the solid line connection. For example, the solid line output connection of Figure 16 has the LED ‘ON’ when input voltage VS is above trip voltage V2, for overvoltage detection. The dashed line output connection has the LED ‘ON’ when VS is below trip voltage V2, for undervoltage detection. |
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