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Application Description
Question 1
When using the HT9274 amplifier as a comparator in my application, the resistors have a value of R1=750K and R2=3.3M, therefore VIN-=2.5*3.3/(3.3+0.75)=2.03V. When the VIN+ voltage rises exceeding 2.03V, the Vo output voltage will only rise to 2.5V slowly after a few seconds. If I change the resistors to R1=7.5K and R2=33K, the rise time will improve but the power consumption will become another issue for my application. How can I solve this problem?
Answer
The HT9274 input structure is composed of PMOS transistors as shown in the datasheet on Page 5. It should be noted that VDD should be 1.0V greater than the voltage on VIN pins for normal working conditions. In this application,
VIN-=2.03V which has a voltage difference of less than 1V when compared with VDD which is equal to 2.5V. This results in a very small PMOS current which gives a slow output voltage rise time. To solve the problem either raise the VDD voltage to a higher level, e.g. 3.5V or halve the value of the
VIN+ voltage and adjust VIN- accordingly. Note that resistors with higher resistance values are recommended to reduce power consumption.
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