MAX9075/MAX9077
Low-Cost, Ultra-Small, 3µA
Single-Supply Comparators
6
Maxim Integrated
Pin Description
FUNCTIONNAME
SOT23
MAX9077
µMAX/SOSC70 SOT23
—1 — Comparator OutputOUT1
1— 1
42 2 GroundGND2
Output of Comparator AOUTA—
—3 —
3— 4 Noninverting Input of Comparator AINA+—
—4 —
2— 3 Inverting Input of Comparator AINA-—
Inverting Comparator InputIN-4
Noninverting Comparator InputIN+3
85 8 Positive Supply VoltageV
CC
5
5— 5
6— 6 Inverting Input of Comparator BINB-—
7— 7 Output of Comparator BOUTB—
Noninverting Input of Comparator BINB+—
MAX9075
PIN
Detailed Description
The MAX9075/MAX9077 feature a 580ns propagation
delay from an ultra-low supply current of only 3µA per
comparator. These devices are capable of single-sup-
ply operation in the 2.1V to 5.5V range. Large internal
output drivers allow rail-to-rail output swing with up to
2mA loads. Both comparators offer a push-pull output
that sinks and sources current.
Comparator Output
The MAX9075/MAX9077 are designed to maintain a
low-supply current during repeated transitions by limit-
ing the shoot-through current.
Noise Considerations, Comparator Input
The input common-mode voltage range for these
devices extends from 0V to V
CC
- 1.2V. Unlike many
other comparators, the MAX9075/MAX9077 can oper-
ate at any differential input voltage within these limits.
Input bias current is typically -5nA if the input voltage is
between the supply rails.
Although the comparators have a very high gain, useful
gain is limited by noise. The comparator has a wide-
band peak-to-peak noise of approximately 70µV.
Applications Information
Adding Hysteresis
Hysteresis extends the comparator’s noise margin by
increasing the upper threshold and decreasing the
lower threshold. A voltage divider from the output of the
comparator sets the trip voltage. Therefore, the trip
voltage is related to the output voltage. Set the hystere-
sis with three resistors using positive feedback, as
shown in Figure 1.
The design procedure is as follows:
1) Choose R3. The leakage current of IN+ may cause a
small error; however, the current through R3 can be
approximately 500nA and still maintain accuracy.
The added supply current due to the circuit at the
trip point is V
CC
/R3; 10MΩ is a good practical value
for R3, as this keeps the current well below the sup-
ply current of the chip.
2) Choose the hysteresis voltage (V
HYS
), which is the
voltage between the upper and lower thresholds. In
this example, choose V
HYS
= 50mV and assume
V
REF
= 1.2V and V
CC
= 5V.
3) Calculate R1 as follows:
R1 = R3 x V
HYS
/V
CC
= 10MΩ x 0.05/5 = 100kΩ
