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ADM6339QARJZ-RL7 Datasheet(PDF) 8 Page - Analog Devices |
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ADM6339QARJZ-RL7 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page ADM6339 Rev. A | Page 8 of 12 THEORY OF OPERATION The ADM6339 is a compact, low power supervisory circuit that is capable of monitoring up to four voltages in a multisupply application. The device includes several factory-set voltage threshold options for monitoring −5.0 V, +1.8 V, +2.5 V, +3.0 V, +3.3 V, and +5.0 V supplies. The ADM6339 is available with one to three adjustable threshold options. The adjustable voltage threshold options available are +1.23 V, +0.62 V, and −0.5 V. See the Ordering Guide section for a list and description of all available options. INPUT CONFIGURATION Built-in hysteresis improves the ADM6339’s immunity to short input transients, without noticeably reducing the threshold accuracy. The internal comparators each have a hysteresis of 0.3% with respect to the reset threshold voltage. (The IN4 input of the ADM6339Q model has a hysteresis of 0.47% with respect to its reset threshold voltage of −0.487 V.) Monitored inputs are resistant to short power supply glitches. Figure 6 depicts the ADM6339 glitch immunity data. To increase noise immunity in noisy applications, place a 0.1 μF capacitor between the IN2 input and ground. Adding capacitance to IN1, IN3, and IN4 also improves noise immunity. IN1 ADM6339 MONITORED SUPPLIES MICROPROCESSOR IN2 RESET IN3 IN4 GND Figure 13. Typical Applications Circuit IN2 must always be used for normal operation because it is the device’s power supply input. Do not allow unused monitor inputs to float or to be grounded. Unused IN3 or IN4 inputs with positive thresholds can be connected directly to the IN2 input. Unused IN4 options with negative thresholds must be tied to a more negative supply. MONITORING NEGATIVE VOLTAGES < −5.0 V A number of ADM6339 models include a pretrimmed threshold option to monitor −5.0 V voltage levels. Use a low impedance resistor divider network similar to that shown in Figure 14 to monitor supplies more negative than −5.0 V. The current through the external resistor divider should be greater than the input current for the −5.0 V monitor options. For an input monitor current error of <1%, the resistor network current should be greater than or equal to 2 mA (for IIN4 = 20 μA maximum). Set R2 = 2.5 kΩ. Calculate R1 based on the desired VINTH reset threshold voltage, using the following equation: R1 = R2((VINTH/VTH) − 1) where: R2 ≤ 2.49 kΩ. VINTH is the desired threshold voltage. VTH is the internal threshold voltage. For example, when monitoring a nominal voltage of −12 V, VINTH = −11.1 V, VTH = −4.63 V, and R2 = 2.49 kΩ. Therefore, using the previous equation, R1 = 3.48 kΩ. R2 R1 VINTH ADM6339 Figure 14. Negative Voltage Monitoring USER ADJUSTABLE THRESHOLD OPTIONS The ADM6339 offers the choice of three adjustable INx input threshold voltages: +1.23 V, +0.62 V, or −0.5 V. When using an adjustable threshold of 1.23 V (typical), to monitor a voltage greater than 1.23 V, connect a resistor divider network to the device as shown in Figure 15. VINTH, the desired threshold voltage, can be expressed as VINTH = 1.23 V((R1 + R2)/(R2)) The ADM6339 has a guaranteed input current of ±0.1 μA on its 1.23 V adjustable input. Resistor values up to 100 kΩ can be used for R2 with <1% error. VINTH R1 R2 VREF = 1.23V ADM6339 Figure 15. Setting the 1.23 V Adjustable Monitor The same approach is taken when using the 0.62 V (typical) adjustable threshold input. Use the following equation to solve for the values of R1 and R2: VINTH = 0.62 V((R1 + R2)/(R2)) The 0.62 V (typical) adjustable threshold input offers high threshold accuracy of ±0.8%. |
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