30 k

Ÿ

240 k

Ÿ

2.2 k

Ÿ

TL7700

CT

510 pF

RESET

VCC

SENSE

5V

RESET

VCC

VSS

Microcontroller

GND

Copyright © 2016, Texas Instruments Incorporated

13

TL7700

www.ti.com

SLVS220G – JULY 1999 – REVISED AUGUST 2016

Product Folder Links: TL7700

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Copyright © 1999–2016, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The TL7700 supply-voltage supervisor allows for any voltage greater than 500mV to be monitored. This flexibility

allows it to be used in many applications from FPGAs and Microcontrollers to Industrial supply monitoring.

9.2 Typical Application

Figure 21 shows an application where the TL7700 device is being used to sense the voltage supply for a

microcontroller that is supplied with 5 V. If the sense voltage drops below 4.5 V, the RESET pin is pulled LOW,

signaling the microcontroller to reset.

Figure 21. 5-V Supply Voltage Supervision

9.2.1 Design Requirements

•

When the TL7700 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

•

The RESET output is an open-collector output, so a pullup resistor is required.

9.2.2 Detailed Design Procedure

The SENSE terminal input voltage, Vs, of the TL7700 typically is 500 mV. By using two external resistors, any

sense voltage over 500 mV can be sensed.

Resistor R1 should be selected first to set the desired hysteresis. See Sense-Voltage Hysteresis Setting for

detailed information on how to set the hysteresis.

Resistor R2 should then be selected based on the R1 value and the desired Vs' voltage. In Figure 18, the

sensing voltage, Vs', is calculated as: Vs' = Vs × (R1 + R2)/R2