SLVSCP7B November   2014  – March 2016 TPS22968-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics (VBIAS = 5 V)
    6. 7.6 Electrical Characteristics (VBIAS = 3.3 V)
    7. 7.7 Electrical Characteristics (VBIAS = 2.5 V)
    8. 7.8 Switching Characteristics
    9. 7.9 Typical Characteristics
      1. 7.9.1 DC Characteristics
      2. 7.9.2 AC Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 ON and OFF Control
      2. 9.3.2 Quick Output Discharge (QOD) (TPS22968-Q1 Only)
      3. 9.3.3 Adjustable Rise Time
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Input Capacitor (Optional)
      2. 10.1.2 Output Capacitor (Optional)
      3. 10.1.3 VIN and VBIAS Voltage Range
        1. 10.1.3.1 Parallel Configuration
        2. 10.1.3.2 Standby Power Reduction
        3. 10.1.3.3 Power Supply Sequencing Without a GPIO Input
        4. 10.1.3.4 Reverse Current Blocking
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Inrush Current
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
    3. 12.3 Thermal Considerations
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Developmental Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Community Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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10 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.

10.1 Application Information

This section highlights some of the design considerations for implementing this device in various applications. A PSPICE model for this device is also available on the product page on www.ti.com for further aid. (See the Device Support section for more information)

10.1.1 Input Capacitor (Optional)

To limit the voltage drop on the input supply caused by transient inrush currents when the switch turns on into a discharged load capacitor, a capacitor must be placed between VIN and GND. A 1-µF ceramic capacitor, CIN, placed close to the pins, is usually sufficient. Higher values of CIN can be used to further reduce the voltage drop during high-current applications. When switching heavy loads, TI recommends to have an input capacitor about 10× higher than the output capacitor to avoid excessive voltage drop.

10.1.2 Output Capacitor (Optional)

Due to the integrated body diode in the NMOS switch, TI highly recommends a CIN greater than CL. A CL greater than CIN can cause the voltage on VOUT to exceed VIN when the system supply is removed. This could result in current flow through the body diode from VOUT to VIN. TI recommends a CIN to CL ratio of 10 to 1 for minimizing VIN dip caused by inrush currents during startup.

10.1.3 VIN and VBIAS Voltage Range

For optimal RON performance, make sure VIN ≤ VBIAS. The device is still functional if VIN > VBIAS, but it will exhibit RON greater than what is listed in the Electrical Characteristics (VBIAS = 5 V) and Electrical Characteristics (VBIAS = 2.5 V) . See Figure 35 for an example of a typical device. Notice the increasing RON as VIN exceeds VBIAS voltage. Be sure to never exceed the maximum voltage rating for VIN and VBIAS.

TPS22968-Q1 C014_SLVSCP7.png
TA = 25°C IOUT = –200 mA
Figure 35. RON vs VIN

10.1.3.1 Parallel Configuration

To increase the current capabilities and lower the RON by approximately 50%, both channels can be placed in parallel as shown in Figure 36 (parallel configuration). With this configuration, the CT1 and CT2 pins can be tied together to use one capacitor, CT, as shown in Figure 36. With a single CT capacitor, the rise time will be half of the typical rise-time value. Refer to the Table 1 for typical timing values.

TPS22968-Q1 Figure35_SLVSCP7.jpg Figure 36. Parallel Configuration Schematic

10.1.3.2 Standby Power Reduction

TPS22968x-Q1 can help to reduce the standby power consumption of a module. Some loads will consume a non-trivial amount of power when turned off. If the power to the load is removed by the load switch, the standby power consumption can be significantly reduced. Figure 37 below shows the Standby Power Reduction Schematic.

TPS22968-Q1 Figure36_SLVSCP7.jpg Figure 37. Standby Power Reduction Schematic

10.1.3.3 Power Supply Sequencing Without a GPIO Input

In many end equipments, there is a need to power up various modules in a predetermined manner. TPS22968x-Q1 can solve the problem of power sequencing without adding any complexity to the overall system. See Figure 38.

TPS22968-Q1 Figure37_SLVSCP7.jpg
VIN1 must be greater VIH.
Figure 38. Power Sequencing Without a GPIO Input Schematic

10.1.3.4 Reverse Current Blocking

In certain applications, it may be desirable to have reverse current blocking. Reverse current blocking prevents current from flowing from the output to the input of the load switch when the device is disabled. With the following configuration, the TPS22968x-Q1 can be converted into a single-channel switch with reverse current blocking. In this configuration, VIN1 or VIN2 can be used as the input and VIN2 or VIN1 is the output. See Figure 39.

TPS22968-Q1 Figure38_SLVSCP7.jpg Figure 39. Reverse Current Blocking Schematic

10.2 Typical Application

This application demonstrates how the TPS22968x-Q1 can be used to power a downstream load with a large capacitance. The example in Figure 40 is powering a 22-µF capacitive output load.

TPS22968-Q1 Front_Page_Schem_SLVSCP7.gif Figure 40. Typical Application Schematic for Powering a Downstream Module

10.2.1 Design Requirements

For this design example, use the values listed in Table 3 as the input parameters.

Table 3. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
VIN 3.3 V
VBIAS 5 V
Output capacitance (CL) 22 µF
Allowable inrush current on VOUT 0.4 A

10.2.2 Detailed Design Procedure

To begin the design process, the designer must know the following:

  • VIN voltage
  • VBIAS voltage
  • Output capacitance (CL)
  • Allowable inrush current on VOUT due to CL capacitor

10.2.2.1 Inrush Current

To determine how much inrush current will be caused by the CL capacitor, use Equation 2.

Equation 2. TPS22968-Q1 Eq2_Iinrush_slvsci4.gif

where

  • IINRUSH = amount of inrush current caused by CL
  • CL = capacitance on VOUT
  • dt = VOUT rise time
  • dVOUT = increase in VOUT during the rise time

Inrush current is proportional to rise time. The rise time is adjustable by use of the CT capacitor. The appropriate rise time can be calculated using the design requirements and the inrush current equation ( Equation 2).

Equation 3. 400 mA = 22 µF × 3.3 V / dt
Equation 4. dt = 182 µs

To ensure an inrush current of less than 400 mA, choose a CT capacitor value that will yield a rise time of more than 182 µs. See the oscilloscope captures in the Application Curves for an example of how the CT capacitor can be used to reduce inrush current. See Table 1 for correlation between rise times and CT values.

An appropriate CL value should be placed on VOUT such that the IMAX and IPLS specifications of the device are not violated.

10.2.3 Application Curves

The two scope captures in Figure 41 and Figure 42 show how the CT capacitor can be used to reduce inrush current.

TPS22968-Q1 tps22968_inrush_vin_3p3v_CL_22uF_Ct_0.gif
VBIAS = 5 V VIN = 3.3 V TA = 25°C
CT = Open CL = 22 µF
Figure 41. Inrush Current Without CT Capacitor
TPS22968-Q1 tps22968_inrush_vin_3p3v_CL_22uF_Ct_220pF.gif
VBIAS = 5 V VIN = 3.3 V TA = 25°C
CT = 220 pF CL = 22 µF
Figure 42. Inrush Current With CT = 220 pF