SLVS651B May   2006  – December 2015 TPS62510

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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Voltage Tracking (OVT)
      2. 7.3.2 Power Good
      3. 7.3.3 Undervoltage Lockout
      4. 7.3.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Soft Start
      2. 7.4.2 100% Duty Cycle Low Dropout Operation
      3. 7.4.3 Power Save Mode Operation (MODE)
      4. 7.4.4 Power Save Mode Transition Thresholds
      5. 7.4.5 Short-Circuit Protection
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Capacitor Selection
        2. 8.2.2.2 Output Filter Design (Inductor and Output Capacitor)
        3. 8.2.2.3 Setting the Output Voltage Using the Feedback Resistor Divider
        4. 8.2.2.4 Inductor Selection
      3. 8.2.3 Application Curves
    3. 8.3 System Example
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Community Resources
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8 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.

8.1 Application Information

The TPS62510 is a high-efficiency step-down converter targeted for operation from a 1.8-V to 3.8-V input voltage rail, ideally suited for 2-cell alkaline or NiMHd applications. The TPS62510 is also ideal as a point-of-load regulator running from a fixed 3.3-V, 2.5-V or 1.8-V input voltage rail.

8.2 Typical Application

Figure 11 shows the adjustable version programming to 1.5 V.

TPS62510 adj_cir_15v_lvs651.gif Figure 11. Adjustable Version Programmed to 1.5 V Example

8.2.1 Design Requirements

The design guideline provides a component selection to operate the device within the recommended operating conditions. The output voltage tracking is not used and the output voltage is programmed using the external voltage divider. The connection of the power good output is shown in one of the system examples.

8.2.2 Detailed Design Procedure

8.2.2.1 Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, a low ESR input capacitor is required for best input voltage filtering, and minimizing the interference with other circuits caused by high input voltage spikes. The converter needs a ceramic input capacitor of 22 μF. The input capacitor may be increased without any limit for better input voltage filtering. The AVIN pin is separated from the power input of the converter. Note that the filter resistor may affect the undervoltage lockout threshold since up to 5 mA can flow via this resistor into the AVIN pin when the converter runs in PWM mode.

Table 1. Input Capacitor Selection

CAPACITOR VALUE CASE SIZE COMPONENT SUPPLIER COMMENTS
22 μF 1206 TDK C3216X5R0J226M Ceramic
22 μF 1206 Taiyo Yuden JMK316BJ226ML Ceramic

8.2.2.2 Output Filter Design (Inductor and Output Capacitor)

The TPS62510 step-down converter has an internal loop compensation. Therefore, the external L-C filter must be selected to work with the internal compensation.

The internal compensation is optimized to operate with an output filter of L = 2.2 μH with an output capacitor of COUT = 22 μF. The output filter has its corner frequency per Equation 6:

Equation 6. TPS62510 q6_fc_lvs651.gif

where

  • L = 2.2 μH
  • CO = 22 μF

As a general rule of thumb, the product L x C should not move over a wide range when selecting a different output filter. This is because the internal compensation is designed to work with a certain output filter corner frequency, as calculated in Equation 6. This is especially important when selecting smaller inductor or output capacitor values that move the corner frequency to higher frequencies. However, when selecting the output filter a low limit for the inductor value exists due to other internal circuit limitations. The minimum inductor value for the TPS62510 should be kept at 2.2 μH. Selecting a larger capacitor value is less critical because the corner frequency drops, causing fewer stability issues.

Table 2. Output Capacitor Selection

L CO
2.2 μH ≥22 μF (ceramic capacitor)
3.3 μH ≥22 μF (ceramic capacitor)(1)
(1) For output currents <800 mA, a 10-μF output capacitor is sufficient.

8.2.2.3 Setting the Output Voltage Using the Feedback Resistor Divider

The external resistor divider sets the output voltage of the converter.

The output voltage is calculated as:

Equation 7. TPS62510 q7_vout_lvs651.gif

where

  • R1 + R2 ≤ 1 MΩ
  • The internal reference voltage is Vref typical = 0.6 V

To keep the operating quiescent current to a minimum, a high impedance feedback divider is selected with
R1 + R2 ≤ 1 MΩ. The sum of R1 and R2 should not be greater than 1 MΩ to avoid possible noise related regulation issues. A feedforward capacitor is needed across the upper feedback resistor to place a zero at a frequency of 25 kHz in the control loop. After selecting the feedback resistor values, the feedforward capacitor is calculated as:

Equation 8. TPS62510 q8_c1_lvs651.gif

where

  • R1 = upper resistor of voltage divider
  • Cff = upper capacitor of voltage divider

Select the capacitor value that is closest to the calculated value.

8.2.2.4 Inductor Selection

For high efficiencies, the inductor should have a low DC resistance to minimize conduction losses. Especially at high switching frequencies where the core material has a higher impact on the efficiency. The inductor value determines the inductor ripple current. The larger the inductor value, the smaller the inductor ripple current, and the lower the conduction losses of the converter. However, larger inductor values cause slower load transient response. Usually, the inductor ripple current as calculated in Equation 9, should be around 20% of the average output current.

To avoid saturation of the inductor, the inductor should be rated at least for the maximum output current of the converter plus the inductor ripple current calculated in Equation 9:

Equation 9. TPS62510 q9_il_vo_lvs651.gif

where

  • f = Switching frequency (1.5 MHz typical)
  • L = Inductor value
  • ΔIL = Peak-to-peak inductor ripple current
  • ILmax = Maximum inductor current

The highest inductor current occurs at maximum VIN.

A more conservative approach is to select the inductor current rating just for the maximum typical switch current limit of the converter of 2 A. See Table 3 for inductor recommendations.

Table 3. Inductor Recommendations

INDUCTOR VALUE COMPONENT SUPPLIER DIMENSIONS I(SAT) / R(DC)
2.2 μH Sumida CDRH2D18/HP 4R7 3.2 mm × 3.2 mm × 2 mm 1.6 A / 60 mΩ
2.2 μH Wuerth 744045002 4.5 mm × 3.2 mm × 2.6 mm 1.6 A / 110 mΩ
2.2 μH Sumida CDRH3D14 4 mm × 4 mm × 1.8 mm 1.75 A / 69 mΩ
2.2 μH Sumida CDRH4D22 5 mm × 5 mm × 2.4 mm 1.8 A / 25.4 mΩ
2.2 μH Sumida CDRH4D28 5 mm × 5 mm × 3 mm 2 A / 31.3 mΩ
2.2 μH Coilcraft MSS5131 5.1 mm x 5.1 mm × 3.1 mm 1.9 A / 23 mΩ
2.2 μH Coilcraft DO1608 6.6 mm × 4.45 mm × 2.92 mm 2.3 A / 28 mΩ
2.2 μH Wuerth 74455022 6.6 mm × 4.45 mm × 2.92 mm 2.3 A / 28 mΩ

8.2.3 Application Curves

TPS62510 eff_v_il_25v_lvs651.gif Figure 12. Efficiency vs Load Current, VOUT = 2.5 V
TPS62510 line_trans_lvs651.gif Figure 14. Line Transient Response
TPS62510 load_t_low_lvs651.gif Figure 16. Load Transient, MODE = Low
TPS62510 rise_load_low_lvs651.gif Figure 18. Rising Load Transient Response, MODE = Low
TPS62510 start_up_lvs651.gif Figure 20. Soft Start-Up
TPS62510 eff_v_il_12v_lvs651.gif Figure 13. Efficiency vs Load Current, VOUT = 1.2 V
TPS62510 load_t_high_lvs651.gif Figure 15. Load Transient Response, MODE = High
TPS62510 fall_load_low_lvs651.gif Figure 17. Falling Load Transient Response, MODE = Low
TPS62510 ps_mode_lvs651.gif Figure 19. Power Save Mode Operation

8.3 System Example

TPS62510 adj_pg_cir_lvs651.gif Figure 21. Adjustable Version Programmed to 1.5 V Using Power Good Example