Datasheet LTC1443, LTC1444, LTC1445 (Analog Devices) - 9

LTC1443/LTC1444/LTC1445
applicaTions inForMaTion
Bypassing the reference can help prevent false tripping of
Hysteresis
the comparators by preventing glitches on the V+ or the Hysteresis can be added to the LTC1444/LTC1445 by con- reference output voltage. Figure 3 shows the bypassed necting a resistor (R1) between the REF and HYST pins, reference output with a square wave applied to the V+ pin. Resistors R1 and R2 set 10mV of hysteresis, while R3 and a second resistor (R2) from HYST to V– (Figure 4). damps the reference response. Note that the comparator The difference between the upper and lower threshold volt- output doesn’t trip. ages or hysteresis voltage band (VHB) is equal to twice the voltage difference between the REF and HYST pins. When more hysteresis is added, the upper threshold increases 3 the same amount as the lower threshold decreases. The 5V V+ TO 8V maximum voltage allowed between REF and HYST is IN A+ 5 + 50mV, producing a maximum hysteresis voltage band of 2 OUT 100mV. If hysteresis is not wanted, the HYST pin should 4 IN A– – be shorted to REF. Acceptable values for IREF range from 14 HYST 0.1µA to 5µA. If 2.4M is chosen for R2, then R1(kΩ) = R1 10k LTC1445 V 8 REF HB (mV). + R2 R3 1.2V – 8 VHB 2.4M 430Ω R1 = V– I REF REF (2)(IREF) C1 9 R1 LTC1445 1.0µF 14 HYST VHB (1.221V – ) 144345 F03a 2 R2 = R2 IREF 144345 F04 9
Figure 3a. V+ Glitching Test Circuit Figure 4. Programmable Hysteresis
8V V+ 5V VREF 2mV/DIV OUT 144345 F03b 2ms/DIV
Figure 3b. V+ Glitching Response
144345fe 9 Document Outline Features Applications Description Absolute Maximum Ratings Typical Application Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Applications Information Package Description Revision History Typical Application Related Parts