SLVS220G July   1999  – August 2016 TL7700

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Sense-Voltage Setting
      2. 8.3.2 Sense-Voltage Hysteresis Setting
      3. 8.3.3 Output Pulse-Duration Setting
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Community Resource
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8 Detailed Description

8.1 Overview

The TL7700 is a bipolar integrated circuit designed for use as a reset controller in microcomputer and microprocessor systems. The SENSE voltage can be set to any value greater than 0.5 V using two external resistors. The hysteresis value of the sense voltage also can be set by the same resistors. The device includes a precision voltage reference, fast comparator, timing generator, and output driver, so it can generate a power-on reset signal in a digital system.

The TL7700 has an internal 1.5-V temperature-compensated voltage reference from which all function blocks are supplied. Circuit function is very stable, with supply voltage in the 1.8-V to 40-V range. Minimum supply current allows use with ac line operation, portable battery operation, and automotive applications.

8.2 Functional Block Diagram

TL7700 fbd_lvs220.gif
A. ICT = 15 µA (Typ), Is = 2.5 µA (Typ)

8.3 Feature Description

8.3.1 Sense-Voltage Setting

The SENSE terminal input voltage, Vs, of the TL7700 typically is 500 mV. By using two external resistors, the circuit designer can obtain any sense voltage over 500 mV. In Figure 18, the sensing voltage, Vs', is calculated as:

Equation 1. Vs' = Vs × (R1 + R2)/R2

where

  • Vs = 500 mV typ at TA = 25°C

At room temperature, Vs has a variation of 500 mV ± 5 mV. In the basic circuit shown in Figure 18, variations of [±5 ± (R1 + R2)/R2] mV are superimposed on Vs.

TL7700 vsense_cx.gif Figure 18. Setting the Sense Voltage

8.3.2 Sense-Voltage Hysteresis Setting

If the sense voltage (Vs') does not have hysteresis in it, and the voltage on the sensing line contains ripples, the resetting of TL7700 is unstable. Hysteresis is added to the sense voltage to prevent such problems. As shown in Figure 19, the hysteresis (Vhys) is added, and the value is determined as:

Equation 2. Vhys = Is × R1

where

  • Is = 2.5 μA typ at TA = 25°C

At room temperature, Is has variations of 2.5 µA ± 0.5 µA. Therefore, in the circuit shown in Figure 18, Vhys has variations of (±0.5 × R1) µV. In circuit design, it is necessary to consider the voltage-dividing resistor tolerance and temperature coefficient in addition to variations in Vs and Vhys.

TL7700 vcc_reset_timing.gif
The sense voltage, Vs', is different from the SENSE terminal input voltage, Vs. Vs normally is 500 mV for triggering.
Figure 19. VCC-RESET Timing Chart

8.3.3 Output Pulse-Duration Setting

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

Equation 3. tpo = Ct × 105 seconds

where

  • Ct is the timing capacitor in farads

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 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.

TL7700 vcc_reset_timing.gif
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