Datasheet MAX965, MAX966, MAX967, MAX968, MAX969, MAX970 (Maxim) - 9

MAX965–MAX970 Single/Dual/Quad, Micropower, Ultra-Low-Voltage, Rail-to-Rail I/O Comparators function below about 1.5V, although the comparators
Noise Considerations
typically continue to operate with a supply voltage as low The comparator has an effective wideband peak-to-peak as 1V. At low supply voltages (<1.6V), the input common- noise of around 10µV. The voltage reference has peak- mode range remains rail-to-rail, but the comparator's to-peak noise approaching 1.0mV with a 0.1µF bypass output sink capability is reduced and propagation delay capacitor. Thus, when a comparator is used with the increases (see Typical Operating Characteristics). reference, the combined peak-to-peak noise is about Figure 1 shows a typical comparator application that monitors 1.0mV. This, of course, is much higher than the individual VCC at 1.6V. Resistor divider R1/R2 sets the voltage components' RMS noise. Avoid capacitive coupling from trip point (VTRIP) at 1.6V. As VCC drops below 1.6V and any output to the reference pin. Crosstalk can significantly approaches 1V, the reference voltage typically falls below increase the references' actual noise. the divider voltage (V+). This causes the comparator output to change state. If OUT's state must be maintained under
Applications Information
these conditions, a latching circuit is required.
Hysteresis Comparator Output
Many comparators oscillate in the linear region of operation The MAX965–MAX970 contain a unique slew-rate- because of noise or undesired parasitic feedback. This controlled output stage capable of rail-to-rail operation tends to occur when the voltage on one input is equal or with an external pull-up resistor. Typical comparators con- very close to the voltage on the other input. The MAX965– sume orders of magnitude more current during switching than MAX970 have internal hysteresis to counter parasitic during steady-state operation. With the MAX965 family effects and noise. In addition, with the use of external of comparators, during an output transition from high to resistor, the MAX965/MAX967/MAX968/MAX969's low, the output slew rate is limited to minimize switching hysteresis can be programmed to as much as ±50mV current. (see the section Adding Hysteresis to the MAX965/ MAX967/MAX968/MAX969).
Voltage Reference
The hysteresis in a comparator creates two trip points: With VCC greater than 1.6V but less than 5.5V, the internal one for the rising input voltage and one for the falling input 1.235V bandgap reference is ±1.5% accurate over the voltage (Figure 2). The difference between the trip points commercial temperature range and ±2.5% accurate over is the hysteresis. When the comparator's input voltages the extended temperature range. The REF output is typical y are equal, the hysteresis effectively causes one comparator capable of sourcing 50µA. To reduce reference noise or input voltage to move quickly past the other, thus taking to provide noise immunity, bypass REF with a capacitor the input out of the region where oscillation occurs. (0.1nF to 0.1µF). VCC VCC 1.6V THRESHOLDS IN+ 1.0V V+ VREF HYSTERESIS R1 t IN- 47kΩ 100kΩ V BAND VREF - VHYST HB V+ VCC R2 OUT 150kΩ GND REF OUT
MAX965
V R1 TRIP = 1.22 + 1 R2 R1 = VTRIP - 1 x R2 1.22 Figure 1. Operation below 1.6V Figure 2. Threshold Hysteresis Band www.maximintegrated.com Maxim Integrated │ 9