ADCMP572BCP AD [Analog Devices], ADCMP572BCP Datasheet - Page 11

• Manufacturer Part Number: ADCMP572BCP
• Description: Ultrafast 3.3 V Single-Supply Comparators
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
COMPARATOR HYSTERESIS
The addition of hysteresis to a comparator is often desirable in a
noisy environment or when the differential input amplitudes are
relatively small or slow moving. The transfer function for a
comparator with hysteresis is shown in Figure 16. If the input
voltage approaches the threshold (0.0 V in this example) from
the negative direction, the comparator switches from a low to a
high when the input crosses +V
becomes −V
the threshold −V
this manner, noise centered on 0.0 V input does not cause the
comparator to switch states unless it exceeds the region
bounded by ±V
The customary technique for introducing hysteresis into a
comparator uses positive feedback from the output back to the
input. A limitation of this approach is that the amount of
hysteresis varies with the output logic levels, resulting in
hysteresis that is not symmetric about the threshold. The
external feedback network can also introduce significant
parasitics that reduce high speed performance, and can even
induce oscillation in some cases.
The ADCMP572/ADCMP573 comparators offer a
programmable hysteresis feature that can significantly improve
the accuracy and stability of the desired hysteresis. By
Figure 16. Comparator Hysteresis Transfer Function
H
/2. The comparator remains in the high state until
H
/2.
H
/2 is crossed from the positive direction. In
–V
2
H
OUTPUT
V
OL
0
V
H
OH
/2. The new switching threshold
+V
2
H
INPUT
Rev. PrB | Page 11 of 16
connecting an external pull-down resistor from the HYS pin to
GND, a variable amount of hysteresis can be applied. Leaving
the HYS pin disconnected disables the feature, and hysteresis is
then less than 1 mV as specified. The maximum hysteresis that
can be applied using this method is approximately ±25 mV.
Figure 17 illustrates the amount of hysteresis applied as a
function of external resistor value. The advantages of applying
hysteresis in this manner are improved accuracy, stability, and
reduced component count. An external bypass capacitor is not
recommended on the HYS pin because it would likely degrade
the jitter performance of the device.
MINIMUM INPUT SLEW RATE REQUIREMENT
As with all high speed comparators, a minimum slew rate
requirement must be met to ensure that the device does not
oscillate as the input signal crosses the threshold. This
oscillation is due in part to the high input bandwidth of the
comparator and the feedback parasitics inherent in the package.
Analog Devices recommends a minimum slew rate of 50 V/µs
to ensure a clean output transition from the ADCMP572/
ADCMP573 comparators unless hysteresis is programmed as
discussed previously.
60
50
40
30
20
10
0
0
Figure 17. Hysteresis vs. R
1
2
ADCMP572/ADCMP573
R
HYS
3
(kΩ)
HYS
Control Resistor
4
5
6