Datasheet LTC1440, LTC1441, LTC1442 (Analog Devices) - 10

LTC1440/LTC1441/LTC1442
U U W U APPLICATIONS INFORMATION
LTC1440/LTC1441/LTC1442 are a family of micropower capacitor of up to 0.01µF without oscillation and by comparators with built-in 1.182V reference. Features inserting a series resistor, capacitance values up to 100µF include programmable hysteresis (LTC1440/LTC1442), can be used (Figure 1). wide supply voltage range (2V to 11V) and the ability of the Figure 2 shows the resistor value required for different reference to drive up to a 0.01µF capacitor without oscil- capacitor values to achieve critical damping. Bypassing lation. The comparators’ CMOS outputs can source up to the reference can help prevent false tripping of the com- 40mA and the supply current glitches, that normally occur parators by preventing glitches on V + or reference load when switching logic states, have been eliminated. transients from disturbing the reference output voltage.
Power Supplies
Figure 3 shows the bypassed reference output with a square wave applied to the V + pin. Resistors R2 and R3 set The comparator family operates from a single 2V to 11V 10mV of hysteresis voltage band while R1 damps the supply. The LTC1440 includes a separate ground for the reference response. Note that the comparator output comparator output stage, allowing a split supply ranging doesn’t trip. from ±1V to ±5.5V. Connecting V – to GND on the LTC1440 will allow single supply operation. If the comparator out- put is required to source more than 1mA, or the supply REFERENCE source impedance is high, V + should be bypassed with a OUTPUT REF 0.1µF capacitor. R1 LTC144X
Comparator Inputs
C1 The comparator inputs can swing from the negative sup- V – ply V – to within 1.3V max of the positive supply V +. The inputs can be forced 300mV below V – or above V + without 1440/1/2 F01 damage and the typical input leakage current is only ±
Figure 1. Damping the Reference Output
10pA.
Comparator Outputs
The LTC1440 comparator output swings between GND 1000 and V + to assure TTL compatibility with a split supply. The LTC1441 and LTC1442 outputs swing between V – and V +. ) 100 Ω The outputs are capable of sourcing up to 40mA and sinking up to 5mA while still maintaining microampere 10 quiescent currents. The output stage does not generate crowbar switching currents during transitions which helps RESISTOR VALUE (k minimize parasitic feedback through the supply pins. 1
Voltage Reference
0.1 0.001 0.01 0.1 1 10 The internal bandgap reference has a voltage of 1.182V CAPACITOR VALUE (µF) referenced to V –. The reference accuracy is 1.5% from 1440/1/2 F02 – 40°C to 85°C. It can source up to 200µA and sink up to
Figure 2. Damping Resistance vs Bypass Capacitor Value
20µA with a 5V supply. The reference can drive a bypass 144012fd 10