Datasheet MAX931, MAX932, MAX933, MAX934 (Analog Devices) - 9

Ultra Low-Power, Low-Cost Comparators with 2% Reference MAX931-MAX934
current falls. The reference will not function below As the input voltage approaches the comparator's about 2.2V, although the comparators will continue to offset, the output begins to bounce back and forth; this operate with a total supply voltage as low as 1V. While peaks when VIN = VOS. (The lowpass filter shown on the MAX934 has comparators that may be used at the graph averages out the bouncing, making the supply voltages below 2V, the MAX931, MAX932, and transfer function easy to observe.) Consequently, the MAX933 may not be used with supply voltages comparator has an effective wideband peak-to-peak significantly below 2.5V. noise of around 0.3mV. The voltage reference has At low supply voltages, the comparators’ output drive is peak-to peak noise approaching 1mV. Thus, when a reduced and the propagation delay increases (see comparator is used with the reference, the combined Typical Operating Characteristics). The useful input peak-to-peak noise is about 1mV. This, of course, is voltage range extends from the negative supply to a much higher than the RMS noise of the individual little under 1V below the positive supply, which is components. Care should be taken in the layout to slightly closer to the positive rail than the device avoid capacitive coupling from any output to the operating from higher supply voltages. Test your reference pin. Crosstalk can significantly increase the prototype over the full temperature and supply-voltage actual noise of the reference. range if operation below 2.5V is anticipated.
__________Applications Information Comparator Output Hysteresis
With 100mV of overdrive, propagation delay is typically Hysteresis increases the comparators’ noise margin by 3µs. The Typical Operating Characteristics show the increasing the upper threshold and decreasing the propagation delay for various overdrive levels. lower threshold (see Figure 2). The MAX931 and MAX934 output swings from V+ to GND, so TTL compatibility is assured by using a
Hysteresis (MAX931/MAX932/MAX933)
+5V ±10% supply. The negative supply does not affect To add hysteresis to the MAX931/MAX932/MAX933, the output swing, and can range from 0V to -5V ±10%. connect resistor R1 between REF and HYST, and connect resistor R2 between HYST and V- (Figure 3). If The MAX932 and MAX933 do not have a GND pin, and no hysteresis is required, connect HYST to REF. When their outputs swing from V+ to V-. Connect V- to ground hysteresis is added, the upper threshold increases by and V+ to a +5V supply to achieve TTL compatibility. the same amount that the lower threshold decreases. The MAX931-MAX934’s unique design achieves an The hysteresis band (the difference between the upper output source current of more than 40mA and a and lower thresholds, VHB) is approximately equal to sink current of over 5mA, while keeping quiescent twice the voltage between REF and HYST. The HYST currents in the microampere range. The output can input can be adjusted to a maximum voltage of REF source 100mA (at V+ = 5V) for short pulses, as long as and to a minimum voltage of (REF - 50mV). The the package's maximum power dissipation is not exceeded. The output stage does not generate crowbar switching currents during transitions, which minimizes feedback through the supplies and helps ensure stability THRESHOLDS without bypassing. IN+
Voltage Reference
The internal bandgap voltage reference has an output HYSTERESIS of 1.182V above V-. Note that the REF voltage is IN- BAND referenced to V-, not to GND. Its accuracy is ±2% in VREF - VHYST VHB the range 0°C to +70°C. The REF output is typically capable of sourcing 15µA and sinking 8µA. Do not bypass the REF output. For applications that require a 1% precision reference, see the MAX921-MAX924 data sheet. OUT
Noise Considerations
Although the comparators have a very high gain, useful gain is limited by noise. This is shown in the Transfer Function graph (see Typical Operating Characteristics). Figure 2. Threshold Hysteresis Band
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