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LTC2905HTS8TRMPBF Datasheet(PDF) 10 Page - Linear Technology |
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LTC2905HTS8TRMPBF Datasheet(HTML) 10 Page - Linear Technology |
10 / 16 page LTC2904/LTC2905 10 29045fd APPLICATIONS INFORMATION Power-Down On power-down, once either V1 or V2 inputs drops below its threshold, RST asserts logic low and RST weakly pulls high. VCC of at least 1V guarantees a logic low of 0.4V at RST. Programming Pins The three 3-state input pins: S1, S2 and TOL should be connected to GND, V1 or left unconnected during normal operation. Note that when left unconnected, the maximum leakage current allowable from the pin to either GND or V1 is 10μA. In margining applications, all the 3-state input pins can be driven using a tri-state buffer. Note however the low and high output of the tri-state buffer has to satisfy the VIL and VIH of the 3-state pin listed in the Electrical Characteristics Table. Moreover, when the tri-state buffer is in the high impedance state, the maximum leakage current allowed from the pin to either GND or V1 is 10μA. Monitor Programming Connecting S1 and S2 to GND, V1 or leaving them open selects the LTC2904/LTC2905 input voltage combina- tions. Table 1 shows the nine possible combinations of nominal input voltages and their corresponding S1, S2 connections. Table 1. Voltage Threshold Programming V1 V2 S1 S2 5.0 3.3 V1 V1 3.3 2.5 Open GND 3.3 1.8 V1 Open 3.3 1.5 Open V1 3.3 1.2 Open Open 2.5 1.8 GND GND 2.5 1.5 GND Open 2.5 1.2 GND V1 2.5 1.0 V1 GND Note: Open = open circuit or driven by a three state buffer in high impedance state with leakage current less than 10μA. Tolerance Programming The three-state input pin, TOL programs the common supply tolerance for both V1 and V2 input voltages (5%, 7.5% or 10%). The larger the tolerance the lower the trip threshold. Table 2 shows the tolerances selection corre- sponding to a particular connection at the TOL pin. Table 2. Tolerance Programming Tolerance TOL 5% V1 7.5% Open 10% GND Threshold Accuracy Reset threshold accuracy is of the utmost importance in a supply sensitive system. Ideally such a system should not reset while supply voltages are within a specified margin below the rated nominal level. Both of the LTC2904/LTC2905 inputs have the same relative threshold accuracy. The specification for LTC2904/LTC2905 is ±1.5% of the pro- grammed nominal input voltage (over the full operating temperature range). For example, when the LTC2904/LTC2905 are programmed to handle a 5V input with 10% tolerance (S1 = S2 = V1 and TOL = GND, refer to Table 1 and Table 2), it does not issue a reset command when V1 is above 4.5V. The typical 10% trip threshold is at 11.5% below the nominal input voltage level. Therefore, the typical trip threshold for the 5V input is 4.425V. With ±1.5% accuracy, the trip threshold range is 4.425V ±75mV over temperature (i.e. 10% to 13% below 5V). This implies that the monitored system must operate reliably down to 4.35V over temperature. The same system using a supervisor with only ±2.5% accuracy needs to work reliably down to 4.25V (4.375V ±125mV)or15%below5V,requiringthemonitoredsystem to work over a much wider operating voltage range. |
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