TLV4021 datasheet(17/36 Pages) TI

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8.4.2 Input (IN)

The TLV40x1 comparators have two inputs: one external input (IN) and one internal input that is connected to

the integrated voltage reference. The comparator rising threshold is trimmed to the reference voltage (VIT+) while

the falling threshold is trimmed to (VIT-). Since the rising and falling thresholds are both trimmed and warranted

in the Electrical Characteristics Table, the TLV40x1 is equally suited for undervoltage and overvoltage detection.

The difference between (VIT+) and (VIT-) is referred to as the comparator hysteresis and is 20 mV for TLV40x1Ry

and 54 mV for TLV4021S5x. The integrated hysteresis makes the TLV40x1 less sensitive to supply-rail noise

and provides stable operation in noisy environments without having to add external positive feedback to create

hysteresis.

The comparator input (IN) is able to swing 5.5 V above (V-) regardless of the device supply voltage. This

includes the instance when no supply voltage is applied to the comparator (VS = 0 V). As a result, the TLV40x1

is referred to as fault tolerant, meaning it maintains the same high input impedance when VS is unpowered or

ramping up. While not required in most cases, in order to reduce sensitivity to transients and layout parasitics for

extremely noisy applications, place a 1 nF to 100 nF bypass capacitor at the comparator input.

For the TLV40x1Ry comparators, the input bias current is typically 10 pA for input voltages between (V-) and

(V+) and the value typically doubles for every 10°C temperature increase. The comparator input is protected

from voltages below (V-) by an internal diode connected to (V-). As the input voltage goes below (V-), the

protection diode becomes forward biased and begins to conduct causing the input bias current to increase

exponentially. A series resistor is recommended to limit the input current when sources have signal content that

is less than (V-).

For the TLV4021S5x, the input bias current is limited by the internal resistor divider with typical impedance of 2M

ohms.

8.4.3 Switching Thresholds and Hysteresis (VHYS)

The TLV40x1 transfer curve is shown in Figure 8-5.

• VIT+ represents the positive-going input threshold that causes the comparator output to change from a logic

low state to a logic high state.

• VIT- represents the negative-going input threshold that causes the comparator output to change from a logic

high state to a logic low state.

• VHYS represents the difference between VIT+ and VIT- and is 20 mV for TLV40x1Ry and 54 mV for

TLV4021S5x.

VIT-

VIT+

VHYS = (VIT+) ± (VIT-)

Figure 8-5. Transfer Curve

VIT+ and VIT- have mV's of variation over temperature. The significant portion of the variation of these parameters

is a result of the internal bandgap voltage from which VIT+ and VIT- are derived. The following hysteresis

histograms demonstrate the performance of the TLV40x1 hysteresis circuitry. Since the bandgap reference is

used to set VIT+ and VIT-, each of these parameters have a tendency to error (track) in the same direction. For

example, if VIT+ has a positive 0.5% error, VIT- would have a tendency to have a similar positive percentage

error. As a result, the variation of hysteresis will never be equal to the difference of the highest VIT+ value of its

range and the lowest VIT- value of its range.

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TLV4021, TLV4031, TLV4041, TLV4051

SNVSB04C – MARCH 2019 – REVISED DECEMBER 2021

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