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Measuring an IC's input resistance

Alec_t

Jul 7, 2015
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The comparator would normally be used for comparing a feedback voltage, from whatever the IC is driving, to a reference voltage. What are you using it for? I don't see why you are driving Vin+ with the MCU.
 

BlackMelon

Aug 7, 2012
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Please see page 6 of the HIP4080A's datasheet. That truth table tells us that the comparator along with HEN come into play to select MOSFETs to be turned on or off. (AHO, ALO, BHO, BLO are 4 MOSFETs in an H-bridge)
 

BlackMelon

Aug 7, 2012
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I am curious about the bias voltage. Here I modified Alec_t circuit by adding 100ohm resistor at the emitter to suppress the sensitivity to the change of R2 (may be because of thermal issue or sth. else).

The 5V-0V pulse was applied like V4 in the file "pulse train", and Vcc was 12V. I viewed V4 as changing of voltage around 2.5V (Vpulse = Vdc + Vac, where Vdc = 2.5V, and Vac is a +2.5/-2.5V square wave). I simulated the Vc bias voltage with the circuit in the file "Bias point". I got Vc around 6V as what I expected.

However, back to the file pulse train, after I applied the Vpulse, the program gave the Vc bias voltage of 647.5mV. Is it supposed to be 6V? What exactly is that value?
 

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BlackMelon

Aug 7, 2012
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I think the HIP4080A is very bizarre. I tried to test the truth table on page 6 of its datasheet. I set up a simple circuit in the attachment. I held DIS pin low to enable the IC, and HEN pin low to disable upper mosfets. According to the truth table, I want to see if I the logic IN+>IN- changes from 0 to 1, the only lower mosfet getting turned on will change from ALO to BLO or not. This was done by holding IN- constant at 3.28Vdc, and tuning the voltage at IN+ by using the voltage divider.
Here is the result:

IN- : Held constant at 3.28Vdc
1) IN+>IN- = 0 (IN+ = +1.2Vdc).............V(BLO) - V(BLS) = 12Vdc, V(ALO) - V(ALS) = 0V
2) IN+>IN- = 1 (IN+ = +4.20Vdc)...........V(BLO) - V(BLS) = 12Vdc, V(BLO) - V(BLS) = 0V

According to the page 6 truth table, in the first case, ALO mosfet was supposed to be "ON" ,V(ALO)-V(ALS) = 12V, and BLO mosfet was supposed to be "OFF", V(BLO)-V(BLS) = 0V. And, it should be the other way around for the second case.

Did I violate something?

Thank You
 

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  • HIP Divider.png
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