Datasheet MAX965, MAX966, MAX967, MAX968, MAX969, MAX970 (Maxim) - 10

MAX965–MAX970 Single/Dual/Quad, Micropower, Ultra-Low-Voltage, Rail-to-Rail I/O Comparators Figure 2 illustrates the case in which IN- has a fixed Due to the internal structure of the input developed for voltage applied, and IN+ is varied. If the inputs were ultra-low-voltage operation, the hysteresis band varies reversed, the figure would be the same, except with an with common-mode voltage. The graph Programmed inverted output. Hysteresis vs. Common-Mode Voltage in the Typical
Adding Hysteresis to the MAX965/MAX967/
Operating Characteristics shows this variation. Notice
MAX968/MAX969
that the hysteresis band increases to almost twice the calculated value toward the ends of the common-mode To add hysteresis to the MAX965/MAX967/MAX968/ range. This is apparent only when programming addi- MAX969, connect resistor R1 between REF and HYST, tional hysteresis using the HYST pin. The hysteresis band and connect resistor R2 between HYST and GND (Figure is constant when HYST is connected to REF. 3). If additional hysteresis is not required, connect HYST to REF. When hysteresis is added, the upper and lower
Adding Hysteresis to the MAX966/MAX970
trip points change by the same amount in opposite direc- The MAX966/MAX970 do not have a HYST pin for pro- tions. The hysteresis band (the difference between the gramming hysteresis. Hysteresis can be generated with upper and lower trip points, VHB) is approximately twice three resistors using positive feedback (Figure 4). This the voltage between HYST and REF. The HYST input method generally draws more current than the method voltage range is from REF down to (REF - 50mV). This using the HYST pin on the MAX965/MAX967/MAX968/ yields a hysteresis band from ±1mV to a maximum of MAX969. Also, the positive feedback method slows hys- ±50mV. Calculate the values of R1 and R2 for the desired teresis response time. Use the following procedure to hysteresis band with the following formulas: calculate the resistor values: R1 = ( 1) Select R3. The leakage current of IN+ is under 5nA, HB V / 2) / IREF so the current through R3 should be at least 500nA R2 = RE (V F − HB (V / 2)) / IREF to minimize errors caused by leakage current. The where I current through R3 at the trip point is (VREF - VOUT) / REF (the current sourced by the reference) does not exceed the REF source capability (12µA typical), and R3. Taking into consideration the two possible output is significantly larger than the HYST leakage current (5nA states and solving for R3 yields two formulas: typical). IREF values between 0.1µA and 4µA are good R3 = VREF / 500nA choices. If 2.4MΩ is chosen for R2 (IREF = 0.5µA), the and equation for R1 and VHB can be approximated as: R3 = (VREF - VCC / 500nA) R1(kΩ) ( = HB V / 2) / 0.5 = HB V (mV) Use the smaller of the two resulting resistor values. For example, if VREF = 1.2V and VCC = 5.0V, then the In the MAX967/MAX968/MAX969, the HYST pin pro- two resistor values are 2.4MΩ and 7.6mΩ. For R3, grams the same hysteresis for all comparators in the choose the 2.2MΩ standard value. package. 2) Choose the hysteresis band required (VHB). For this example, choose 50mV. V +1.6V TO +5.5V CC R3 IREF REF VCC
MAX965
R1 R4 V R1
MAX967
IN
MAX968 MAX969
VCC OUT R2 HYST GND R2 GND
MAX966 MAX970
VREF Figure 3. Programming the HYST Pin Figure 4. External Hysteresis www.maximintegrated.com Maxim Integrated │ 10