6 Detailed Description

6.1 Overview

The TL331 family is a single comparator with the ability to operate up to 36V on the supply pin. This standard

device has proven ubiquity and versatility across a wide range of applications. This is due to its very wide supply

voltages range (2V to 36V), low Iq, and fast response.

The open-collector output allows the user to configure the output's logic low voltage (VOL) and can be utilized to

enable the comparator to be used in AND functionality.

The TL331B and TL391B are performance upgrades to standard TL331 using the latest process technologies

allowing for lower offset voltages, lower input bias and supply currents and faster response time over an

extended temperature range. The TL331B can drop-in replace the "I" or "K" versions of TL331. The TL391B is

an alternate pinout for replacing competitive devices.

6.2 Functional Block Diagram

- Input

Q2

Q1

Q3

Q4

Q9

Q10

Q11

Q5

Q6

D1

D2

D3

D4

Q7

Q8

Q12

+ Input

Output

VCC

Internal

Bias

Itail

I1

I2

Q13

Q14

ESD

ESD

VCM

Clamp

Q15

6.3 Feature Description

TL331x family consists of a PNP Darlington pair input, allowing the device to operate with very high gain and fast

response with minimal input bias current. The input Darlington pair creates a limit on the input common mode

voltage capability, allowing TL331x to accurately function from ground to VCC – 1.5V differential input. In later

revisions, a clamp was added around Q3 to mimic the outside-of-input voltage range behavior of the original

classic silicon.

The output consists of an open collector NPN (pull-down or low side) transistor. The output NPN will sink current

when the negative input voltage is higher than the positive input voltage and the offset voltage. The VOL is

resistive and will scale with the output current. Please see the "Output Low Voltage vs. Output Sinking Current"

graphs in Typical Characteristics for VOL values with respect to the output current.

6.4 Device Functional Modes

6.4.1 Voltage Comparison

The TL331x operates solely as a voltage comparator, comparing the differential voltage between the positive

and negative pins and outputting a logic low or high impedance (logic high with pull-up) based on the input

differential polarity.

TL331, TL331B, TL391B

SLVS238L – AUGUST 1999 – REVISED NOVEMBER 2024

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