SPAS093C December   2009  – September 2015 TPS2505

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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 (Shared Boost, LDO and USB)
    6. 6.6  Electrical Characteristics (Boost Only)
    7. 6.7  Electrical Characteristics (USB1/2 Only)
    8. 6.8  Electrical Characteristics (LDO and Reset Only)
    9. 6.9  Recommended External Components
    10. 6.10 Dissipation Ratings
    11. 6.11 Typical Characteristics
  7. Parameter Measurement Information
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  PGND
      2. 8.3.2  IN
      3. 8.3.3  EN
      4. 8.3.4  GND
      5. 8.3.5  ILIM1/2
      6. 8.3.6  RESET
      7. 8.3.7  LDOOUT
      8. 8.3.8  LDOIN
      9. 8.3.9  ENLDO
      10. 8.3.10 FAULT1/2
      11. 8.3.11 ENUSB1/2
      12. 8.3.12 USB1/2
      13. 8.3.13 AUX
      14. 8.3.14 SW
      15. 8.3.15 Thermal Pad
      16. 8.3.16 Boost Converter
        1. 8.3.16.1 Start-Up
        2. 8.3.16.2 Normal Operation
        3. 8.3.16.3 Low-Frequency Mode
        4. 8.3.16.4 No-Frequency Mode
        5. 8.3.16.5 Pulsed Frequency Mode (PFM) Light-Load Operation
        6. 8.3.16.6 Overvoltage Protection
        7. 8.3.16.7 Overload Conditions
        8. 8.3.16.8 Determining the Maximum Allowable AUX and USB1/2 Current
      17. 8.3.17 USB Switches
        1. 8.3.17.1 Overview
        2. 8.3.17.2 Overcurrent Conditions
        3. 8.3.17.3 FAULT1/2 Response
        4. 8.3.17.4 Undervoltage Lockout
        5. 8.3.17.5 Programming the Current-Limit Threshold Resistor RILIM
      18. 8.3.18 3.3-V LDO
      19. 8.3.19 Reset Comparator
      20. 8.3.20 Thermal Shutdown
      21. 8.3.21 Component Recommendations
        1. 8.3.21.1 Boost Inductor
        2. 8.3.21.2 IN Capacitance
        3. 8.3.21.3 AUX Capacitance
        4. 8.3.21.4 USB Capacitance
        5. 8.3.21.5 ILIM1/2 and FAULT1/2 Resistors
    4. 8.4 Device Functional Modes
  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
        1. 9.2.2.1 Step-by-Step Design Procedure
        2. 9.2.2.2 Switching Frequency
        3. 9.2.2.3 AUX Voltage
        4. 9.2.2.4 Determine Maximum Total Current (IAUX + ILDO + IUSB1 + IUSB2 )
        5. 9.2.2.5 Power Inductor
        6. 9.2.2.6 Output AUX Capacitor Selection
        7. 9.2.2.7 Output USB1/2 Capacitor Selection
        8. 9.2.2.8 Input Capacitor Selection
          1. 9.2.2.8.1 Current-Limit Threshold Resistor RILIM
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Community Resources
    2. 12.2 Trademarks
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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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 TPS2505 is a USB switch device enabling a 5-V supply from a single Li-Ion battery, regulated supply, or 2- to 3-cell NiCd , NiMH, or alkaline. This device is targeted toward keyboard, printer, camera, picture frame applications, and other handheld or remote applications.

9.2 Typical Application

TPS2505 typ_app2_pas093.gif

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 2 as the input parameters.

Table 2. Design Parameters

PARAMETER EXAMPLE VALUE
Input voltage range (VIN) 2.7 V to 4.2 V
AUX voltage (VAUX) 5.1 V (internally fixed)
Input ripple voltage (ΔVIN) 15 mV
AUX ripple voltage (ΔVAUX) 50 mV
AUX current (IAUX) 0.3 A
LDO current (ILDO) (powered from AUX) 0.1 A
USB1 current (IUSB1 ) 0.5 A
USB2 current (IUSB2 ) 0.1 A
Total current (ITOTAL = IAUX + ILDO + IUSB1 + IUSB2) 1 A
Efficiency target, nominal 90%
Switching frequency (fSW) 1 MHz

9.2.2 Detailed Design Procedure

9.2.2.1 Step-by-Step Design Procedure

The following design procedure provides an example for selecting component values for the TPS2505.

The following design parameters are needed as inputs to the design process.

  • Input voltage range
  • Output voltage on AUX
  • Input ripple voltage
  • Output ripple voltage on AUX
  • Output current rating of AUX rail
  • Output current rating of USB rail
  • Nominal efficiency target
  • Operating frequency

A power inductor, input and output filter capacitors, and current-limit threshold resistor are the only external components required to complete the TPS2505 boost-converter design. The input ripple voltage, AUX ripple voltage, and total output current affect the selection of these components.

9.2.2.2 Switching Frequency

The switching frequency of the TPS2505 is internally fixed at 1 MHz for the specified VIN range.

9.2.2.3 AUX Voltage

The AUX voltage of the TPS2505 is internally fixed at 5.1 V.

9.2.2.4 Determine Maximum Total Current (IAUX + ILDO + IUSB1 + IUSB2 )

Using Figure 1, the maximum total current at VIN = 2.7 V is 1 A using the conservative line. The design requirements are met for this application.

9.2.2.5 Power Inductor

The inductor ripple current, Δi, should be at least 20% of the average inductor current to avoid erratic operation of the peak-current-mode PWM controller. Assume an inductor ripple current, Δi, which is 30% of the average inductor current and a power-converter efficiency, η, of 90%. Using the minimum input voltage, the average inductor current at VIN = 2.7 V is:

Equation 4. TPS2505 eq_iin_pas093.gif
TPS2505 waveform_currboostind_pas093.gif Figure 11. Waveform of Current in Boost Inductor

The corresponding inductor ripple current is:

Equation 5. TPS2505 eq_deltai_pas093.gif

Verify that the peak inductor current is less than the 3-A peak switch current:

Equation 6. TPS2505 eq_il_pk_pas093.gif

The following equation estimates the duty cycle of the low-side SWN MOSFET:

Equation 7. TPS2505 eq_D_pas093.gif

where

  • RSWN is the low-side control MOSFET ON-resistance
  • RSWP is the high-side synchronous MOSFET ON-resistance
  • RL is an estimate of the inductor DC resistance

The following equation calculates the recommended inductance for this design.

Equation 8. TPS2505 eq_L_pas093.gif

The RMS inductor current is:

Equation 9. TPS2505 eq_il_rms_pas093.gif

Select a Coilcraft LPS4018-222ML inductor. This 2.2-µH inductor has a saturation current rating of 2.7 A and an RMS current rating of 2.3 A. See Component Recommendations for specific additional information.

9.2.2.6 Output AUX Capacitor Selection

The AUX output capacitor, CAUX, discharges during the PWM MOSFET on-time, resulting in an output ripple voltage of ΔVAUX. ΔVAUX is largest at maximum load current.

Equation 10. TPS2505 eq_caux_pas093.gif
Equation 11. TPS2505 eq_caux_min_pas093.gif

Ceramic capacitors exhibit a DC bias effect, whereby the capacitance falls with increasing bias voltage. The effect is worse for capacitors in smaller case sizes and lower voltage ratings. X5R and X7R capacitors exhibit less DC bias effect than Y5V and Z5U capacitors.

Select a TDK C3225X5R1A226M 22-µF, 10-V X5R ceramic capacitor to allow for a 50% drop in capacitance due to the DC bias effect. See Component Recommendations for specific additional information.

9.2.2.7 Output USB1/2 Capacitor Selection

The USB1/2 output capacitors provide energy during a load step on the USB outputs. The TPS2505 does not require a USB output capacitor, but many USB applications require that downstream-facing ports be bypassed with a minimum of 120-μF, low-ESR capacitance.

Select a Panasonic EEVFK1A151P 150-μF, 10-V capacitor.

9.2.2.8 Input Capacitor Selection

The ripple current through the input filter capacitor is equal to the ripple current through the inductor. If the ESL and ESR of the input filter capacitor are ignored, then the required input filter capacitance is:

Equation 12. TPS2505 eq_cin_pas093.gif

Select a TDK C2012X5R1A106K 10-µF, 10-V, X5R, size 805 ceramic capacitor. The capacitance drops 20% at 3.3-V bias, resulting in an effective capacitance of 8 µF.

An additional 0.1-µF ceramic capacitor should be placed locally from IN to GND to prevent noise from coupling into the device if the input capacitor cannot be located physically near to the device.

In applications where long, inductive cables connect the input power supply to the device, additional bulk input capacitance may be necessary to minimize voltage overshoot. See Component Recommendations for specific additional information.

9.2.2.8.1 Current-Limit Threshold Resistor RILIM

The current-limit threshold IOS of the power switches are externally adjustable by selecting the RILIM1/2 resistors. To eliminate the possibility of false tripping, RILIM1/2 should be selected so that the minimum tolerance of the current-limit threshold is greater than the maximum specified USB load, IUSB.

It is also important to account for IOS shifts due to variation in VIN and IAUX. This shift due to the additional loading in AUX can add up to ±75 mA of variation to the IOS as calculated according to Programming the Current-Limit Threshold Resistor RILIM. Select RILIM1 so that the minimum current-limit threshold equals 600 mA to ensure a minimum IUSB1 current-limit threshold of 525 mA. In the same way, select RILIM2 so that the minimum current-limit threshold equals 200 mA to ensure a minimum IUSB2 current-limit threshold of 125 mA.

Equation 13. TPS2505 eq_rilim12_pas093.gif
Equation 14. TPS2505 eq_rilim1_pas093.gif
Equation 15. TPS2505 eq_rilim2_pas093.gif

Choose the next smaller 1% resistor, which are 34.8 kΩ for RLIM1 and 95.3 kΩ for RLIM2.

9.2.3 Application Curves

TPS2505 g_boosteff_outcurr_pas093.gif Figure 12. Boost Efficiency vs Output Current
TPS2505 g_boostloadtransresp_pas093.gif
Figure 14. Boost Load Transient Response, 500 mA - 1 A, USB1/2 Enabled
TPS2505 g_boostout_loadcurr_pas093.gif Figure 13. Boost Output Voltage vs Load Current
TPS2505 g_ldoloadtranresp_0_200_pas093.gif Figure 15. LDO Load Transient Response 0 mA - 200 mA