TL7700CMPWPSEP datasheet(12/25 Pages) TI1

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tpo

RESET

Vhys

VCC

1.5 V

Vs’

TL7700-SEP

SLVSF13 – MARCH 2019

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Product Folder Links: TL7700-SEP

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Feature Description (continued)

8.3.3 Output Pulse-Duration Setting

Constant-current charging starts on the timing capacitor when the sensing-line voltage reaches the TL7700-SEP

sense voltage. When the capacitor voltage exceeds the threshold level of the output drive comparator, RESET

changes from a low to a high level. The output pulse duration is the time between the point when the SENSE-pin

voltage exceeds the threshold level and the point when the RESET output changes from a low level to a high

level. When the TL7700-SEP is used for system power-on reset, the output pulse duration, tpo, must be set

longer than the power rise time. The value of tpo is:

tpo = Ct × 10

5 seconds

where

•

Ct is the timing capacitor in farads

(3)

There is a limit on the device response speed. Even if Ct = 0, tpo is not 0, but approximately 5 µs to 10 µs.

Therefore, when the TL7700-SEP is used as a comparator with hysteresis without connecting Ct, switching

speeds (tr/tf, tpo/tpd, and so forth) must be considered.

8.4 Device Functional Modes

Figure 20 describes how the RESET output pin responds to a change in the voltage at the SENSE pin. When the

SENSE pin drops below 500 mV, the RESET pin is pulled low.

NOTE: The sense voltage, Vs', is different from the SENSE terminal input voltage, Vs. Vs normally is 500 mV for triggering.

Figure 20. VCC RESET Response and Timing

TL7700CMPWPSEP Datasheet(PDF) 12 Page - Texas Instruments