LM397MFSLASHNOPB datasheet(10/19 Pages) TI1

10 / 19 page

200

400

800

1200

1400

2000

-100

TIME (ns)

VOD = 50mV

VOD = 5mV

OVERDRIVE

VOLTAGE (VOD)

VS = 5V, RPULL-UP = 5.1k: TO VS

CL = 15pF TO GND

200

400

800

1200

1400

2000

-100

TIME (ns)

VOD = 50mV

VOD = 5mV

OVERDRIVE

VOLTAGE (VOD)

VS = 5V, RPULL-UP = 5.1k: TO VS

CL = 15pF TO GND

LM397

SNOS977E – MAY 2001 – REVISED OCTOBER 2015

www.ti.com

8.2.2.1 Input Voltage Range

When choosing the input voltage range, the input common mode voltage range (VCM) must be taken in to

account. If temperature operation is above or below 25°C the VCM can range from 0 V to VS – 1.5 V. This limits

the input voltage range to as high as VS – 1.5 V and as low as 0 V. Operation outside of this range can yield

incorrect comparisons.

Below is a list of input voltage situation and their outcomes:

1. When both IN– and IN+ are both within the common mode range:

(a) If IN– is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking

current

(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

8.2.2.2 Minimum Overdrive Voltage

Overdrive Voltage is the differential voltage produced between the positive and negative inputs of the comparator

over the offset voltage. To make an accurate comparison; the overdrive voltage should be higher than the input

offset voltage. Overdrive voltage can also determine the response time of the comparator, with the response time

decreasing with increasing overdrive.

8.2.2.3 Output and Drive Current

Output current is determined by the pullup resistance (RPULLUP) and VS voltage. The output current will produce a

output low voltage (VOL) from the comparator. In which VOL is proportional to the output current. Use Figure 3 to

determine VOL based on the output current. The output current can also effect the transient response.

8.2.3 Application Curves

Figure 11. Response Time for Various Input Overdrives –

Figure 10. Response Time for Various Input Overdrives –

tPLH

tPHL

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