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LTC1842 Datasheet(PDF) 7 Page - Linear Technology |
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LTC1842 Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page 7 LTC1841/LTC1842/LTC1843 APPLICATIONS INFORMATION The LTC1841/LTC1842/LTC1843 are dual micropower comparators with a built-in 1.182V reference (LTC1842/ LTC1843). Features include programmable hysteresis, wide supply voltage range (2V to 11V) and the ability for the reference to drive up to a 0.01 µF capacitor without oscillation. The comparators’ open-drain outputs can typi- cally sink greater than 20mA and the supply current glitches that normally occur when switching logic states have been eliminated. Power Supplies The comparators operate from a single 2V to 11V (2.5V to 11V for LTC1842/LTC1843) or dual ±1V to ±5.5V supply ( ±1.25V to ±5.5V for LTC1842/LTC1843). If the reference output is required to source more than 1mA or the supply source impedance is high, V + should be bypassed with a 0.1 µF capacitor. Comparator Inputs The comparators’ input can swing from the negative supply V – to within 1.3V (max) of the positive supply V +. The input can be forced 300mV below V – or above V + without damage and the typical input leakage current is only ±10pA. Comparator Outputs Each comparator output is an open-drain pull-down to V– typically capable of sinking greater than 20mA. The low output leakage current while in three-state mode allows a high value pull-up resistor to be used. The open-drain outputs can be wire OR-ed or used in level shifting applications. Voltage Reference The internal bandgap reference has an output voltage of 1.182V referenced to V –. The reference accuracy is 1.5% from – 40 °C to 85°C. It can typically source greater than 1mA and sink up to 10 µA with a 5V supply. The reference can drive a bypass capacitor of up to 0.01 µF without oscillation. By inserting a series resistor, capacitance values up to 100 µF can be used (Figure 1). Figure 1. Damping the Reference Output Figure 3 shows the bypassed reference output with a square wave applied to the V + pin. Resistors R2 and R3 set a 10mV hysteresis voltage band while R1 damps the reference response. Note that the comparator output doesn’t trip. CAPACITOR VALUE ( µF) 0.001 0.1 10 0.01 0.1 10 1 1841/43 F02 1 100 Figure 2. Damping Resistance vs Bypass Capacitor Value LTC1843 V – REF R1 C1 REFERENCE OUTPUT 1841/43 F01 Figure 2 shows the resistor value required for different capacitor values to achieve critical damping. Bypassing the reference can help prevent false tripping of the com- parators by preventing glitches on V + or reference load transients from disturbing the reference output voltage. |
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Similar Description - LTC1842_15 |
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