b. If IN- is lower than IN+ and the offset voltage, the output is high impedance and the output transistor is

not conducting

2. When IN- is higher than common mode and IN+ is within common mode, the output is low and the output

transistor is sinking current

3. When IN+ is higher than common mode and IN- is within common mode, the output is high impedance and

the output transistor is not conducting

4. When IN- and IN+ are both higher than common mode, the output is low and the output transistor is sinking

current. The "B" version output will go high.

8.2.2.2 Minimum Overdrive Voltage

The overdrive voltage is the differential voltage produced between the positive and negative inputs of the

comparator over the offset voltage (VIO). To make an accurate comparison the overdrive voltage (VOD) must

be higher than the input offset voltage (VIO). The overdrive voltage can also determine the response time of

the comparator, with the response time decreasing as the overdrive increases. Figure 8-2 and Figure 8-3 show

positive and negative response times with respect to overdrive voltage.

8.2.2.3 Output and Drive Current

Output current is determined by the load/pull-up resistance and logic/pull-up voltage. The output current will

produce an output low voltage (VOL) which is proportional to the output current. Use Figure 6-19, Figure 6-20,

and Figure 6-21 to determine VOL based on the output current.

The output current can also effect the transient response. More will be explained in the next section.

8.2.2.4 Response Time

The transient response can be determined by the load capacitance (CL), load or pullup resistance (RPULLUP), and

equivalent collector-emitter resistance (RCE).

Use Equation 1 and Equation 2 to calculate the approximate values of the rise time (tr) and fall time (tf).

tP ≈ RPULLUP × CL

(1)

tN ≈ RCE × CL

(2)

To find the value of RCE, use the slope of Figure 6-35 in the linear region at the desired temperature, or divide

VOL by IO.

8.2.3 Application Curves

The following curves were generated with 5 V on VCC and VLOGIC, RPULLUP = 5.1 kΩ, and 50-pF scope probe.

±1

0

1

2

3

4

5

6

0.0

0.5

1.0

1.5

2.0

2.5

Time (us)

5mV OD

20mV OD

100mV OD

C001

Figure 8-2. Response Time for Various Overdrives

Negative Transition

±1

0

1

2

3

4

5

6

0.0

0.5

1.0

1.5

2.0

2.5

Time (us)

5mV OD

20mV OD

100mV OD

C001

Figure 8-3. Response Time for Various Overdrives

Positive Transition

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SLCS142G – DECEMBER 2003 – REVISED MARCH 2023

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