SLVSBO4C October   2012  – December 2014

UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Description (continued)
  6. Device Voltage Options
  7. Pin Configuration and Functions
  8. Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 Handling Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Typical Characteristics
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Step-Down (Buck) Converter Operation
      2. 9.3.2 Programming OUT Regulation Voltage and VIN_OK
      3. 9.3.3 Nano-Power Management and Efficiency
    4. 9.4 Device Functional Modes
      1. 9.4.1 Enable Controls
      2. 9.4.2 Startup Behavior
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 TPS62737 3-Resistor Typical Application Circuit
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Inductor Selection
          2. 10.2.1.2.2 Output Capacitor Selection
          3. 10.2.1.2.3 Input Capacitor Selection
          4. 10.2.1.2.4 Resistor Selection
        3. 10.2.1.3 Application Curves
      2. 10.2.2 TPS62736 4-Resistor Typical Application Circuit
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
        3. 10.2.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
    2. 13.2 Related Links
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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

The TPS62736/7 are step down DC-DC converters. Their low quiescent currents make them ideal for battery powered systems that are operated at low duty cycles in order to achieve low total power levels.

10.2 Typical Applications

10.2.1 TPS62737 3-Resistor Typical Application Circuit

application_737_drawing_slvsbo4.gifFigure 52. TPS62737 3-Resistor Typical Application Circuit

10.2.1.1 Design Requirements

A 1.8-V, up to 200 mA regulated power rail is needed. The VIN_OK comparator should indicate when the input voltage drops below 2.9 V. No large load transients are expected.

10.2.1.2 Detailed Design Procedure

The recommended 10-µH inductor (TOKO DFE252012C) and 22-µF input capacitor are used. Since no large load transients are expected, the minimum 22-µF output capacitor is used. Had a large load transient been expected, we would have sized the capacitor using ITRAN = COUT x ΔVOUT / ΔTIME where ΔVOUT is amount of VOUT droop allowed for the time of the transient.

First set RSUM = R1 + R2 + R3 = 13 MΩ then solve Equation 2 for R1 = VBIAS x RSUM / VIN_OK = 1.21 V x 13 MΩ / 2.9 V = 5.42 MΩ → 5.49 MΩ as the closest 1 % resistor.

Then solve Equation 2 for R2 = VBIAS x RSUM / VOUT - R1 = 1.21 V x 13 MΩ / 1.8 V - 5.42 MΩ = 3.32 MΩ → 3.4 MΩ as the closest 1% resistor.

Finally R3 = RSUM - R1 - R2 = 13 MΩ - 5.42 MΩ - 3.32 MΩ = 4.26 MΩ → 4.32 MΩ as the closest 1% resistor.

These values yield VOUT = 1.79 V and VIN_OK threshold = 2.91 V.

If using 4 resistors, see Resistor Selection for guidance on sizing the resistors.

10.2.1.2.1 Inductor Selection

The internal-control circuitry is designed to control the switching behavior with a nominal inductance of 10 µH ± 20%. The saturation current of the inductor' should be at least 25% higher than the maximum cycle-by-cycle current limit per the electrical specs table (ILIM) in order to account for load transients.  Because this device is a hysteretic controller, it is a naturally stable system (single order transfer function).  However, the smaller the inductor value is, the faster the switching currents are.  The speed of the peak current detect circuit sets the inductor of the TPS62736 lower bound to 4.7 µH.  When using a 4.7 µH, the peak inductor current will increase when compared to that of a 10-µH inductor. The steady-state operation with a 4.7-µH inductor with a 50-mA load for the TPS62736 is shown in Figure 65.

A list of inductors recommended for this device is shown in Table 4.

Table 4. Recommended Inductors

INDUCTANCE (µH) DIMENSIONS (mm) PART NUMBER MANUFACTURER
10 2.0 x 2.5 x 1.2 DFE252012C-H-100M Toko
10 4.0 x 4.0 x 1.7 LPS4018-103M Coilcraft
4.7 (TPS62736 only) 2.0 x 2.5 x 1.2 DFE252012R-H-4R7M Toko

10.2.1.2.2 Output Capacitor Selection

The output capacitor is chosen based on transient response behavior and ripple magnitude.  The lower the capacitor value, the larger the ripple will become and the larger the droop will be in the case of a transient response.  It is recommended to use at least a 22-µF output capacitor for most applications.

10.2.1.2.3 Input Capacitor Selection

The bulk input capacitance is recommended to be a minimum of 4.7 µF ± 20% for the TPS62736 and 22 µF ± 20% for the TPS62737.  This bulk capacitance is used to suppress the lower frequency transients produced by the switching converter. There is no upper bound to the input-bulk capacitance. In addition, a high-frequency bypass capacitor of 0.1 µF is recommended in parallel with the bulk capacitor.  The high-frequency bypass is used to suppress the high-frequency transients produced by the switching converter.

10.2.1.2.4 Resistor Selection

Equation 1 to Equation 4 are the equations for sizing the external resistors to set the VIN_OK threshold and VOUT regulation value. The spreadsheet at SLVC489 can help size the external resistors.

10.2.1.3 Application Curves

See efficiency, line regulation, and load regulation curves at Figure 30, Figure 37, and Figure 36.

737_steady_3p6vin_SLVSBO4.gif
V(IN) = 3.6 V bench power supply
R(OUT) = 100 kΩ
Figure 53. Steady State Operation
737_fast_ramp_SLVSBO4.gif
V(IN) = power amplifier ramped from 0 V to 5 V to 0 V
Figure 55. Power Management Response
737_LNT_SLVSBO4.gif
V(IN) = 3.6 V -> 4.6 V -> 4.6 V from bench power supply
R(OUT) = 9 Ω
Figure 57. Line Transient Response
737_slow_ramp_SLVSBO4.gif
V(IN) = power amplifier ramped from 0 V to 5 V to 0 V
EN1 = low; EN2 = high
Figure 59. Startup Behavior with Slow Ramping
VIN
737_EN2_startup_SLVSBO4.gif
V(IN) = 3.6 V bench power supply
EN1 = low; EN2 transitioned from low to high
R(OUT) = 1 kΩ
Figure 61. Standby-Mode Startup Behavior
737_steady_state_SLVSBO4.gif
V(IN) = 3.6 V bench power supply
R(OUT) = 9 Ω
Figure 54. Steady State Operation
737_LT_SLVSBO4.gif
V(IN) = 3.6 V bench power supply + additional C(IN) = 100 uF
R(OUT) = open to 9 Ω to open
Figure 56. Load Transient Response
737_IR_Pulse_SLVSBO4.gif
V(IN) = 4.0 V bench supply + additional C(IN) = 100 uF
VOUT resistors modified to provide 2.5 V
I(OUT) = 200 mA every 1 us
Figure 58. IR Pulse Transient Response
737_EN1_startup_SLVSBO4.gif
V(IN) = 3.6 V bench power supply
EN2 = high; EN1 transitioned from high to low
R(OUT) = 1 kΩ
Figure 60. Ship-Mode Startup Behavior

10.2.2 TPS62736 4-Resistor Typical Application Circuit

application2_drawing_slvsbo4.gifFigure 62. TPS62736 4-Resistor Typical Application Circuit

10.2.2.1 Design Requirements

A 2.5-V, up to 50-mA regulated power rail is needed. The VIN_OK comparator should indicate when the input voltage drops below 2.9 V. No large load transients are expected.

10.2.2.2 Detailed Design Procedure

The recommended 10-µH inductor (TOKO DFE252012C) and 4.7-µF input capacitor are used. Since no large load transients are expected, the minimum 22-µF output capacitor is used. Had a large load transient been expected, we would have sized the capacitor using ITRAN = COUT x ΔVOUT / ΔTIME where ΔVOUT is amount of VOUT droop allowed for the time of the transient.

First set RSUM = R1 + R2 = R3 + R4 = 13 MΩ then solve Equation 4 for R1 = VBIAS x RSUM / VIN_OK = 1.21 V x 13 MΩ / 2.9 V = 5.42 MΩ → 5.36 MΩ as the closest 1 % resistor.

Then R2 = RSUM - R1 = 13 MΩ - 5.42 MΩ = 7.58 MΩ → 7.5 MΩ as the closest 1% resistor.

Solve Equation 3 for R4 = VBIAS x RSUM / VOUT = 1.21 V x 13 MΩ / 2.5 V = 6.29 MΩ → 6.34 MΩ as the closest 1% resistor.

Finally R3 = RSUM - R3 = 13 MΩ - 6.29 MΩ = 6.71 MΩ → 6.81 MΩ as the closest 1% resistor.

These values yield VOUT = 2.51 V and VIN_OK threshold = 2.90 V.

If using 3 resistors, see Resistor Selection for guidance on sizing the resistors.

10.2.2.3 Application Curves

See efficiency, load regulation and line regulation graphs at Figure 1, Figure 7 and Figure 8 respectively.

figure26_slvsbno4.gif
V(IN) = 3.0 V bench power supply
R(OUT) = 50 Ω
Figure 63. Steady State Operation
figure28_slvsbno4.gif
V(IN) = 3.0 V bench power supply
VOUT resistors changed to provide 1.8 V; L = 4.7 uH
R(OUT) = 100 kΩ
Figure 65. Steady State Operation
figure31_slvsbno4.gif
V(IN) = 3.0 V -> 5.0 V from bench power supply
R(OUT) = 50 Ω
Figure 67. Line Transient Response
figure33_slvsbno4.gif
V(IN) = 4.0 V from bench power supply + additional CIN = 100 uF
I(OUT) = 200 mA every 1us
Figure 69. IR Pulse Transient Response
figure35_slvsbno4.gif
V(IN) = 4.0 V from bench power supply
VOUT resistors modified to provide 1.8 V
EN1 = low, EN2 transitioned low to high
Figure 71. Standby-Mode Startup Behavior
figure29_slvsbno4.gif
V(IN) = 3.0 V bench power supply
R(OUT) = 100 kΩ
Figure 64. Steady State Operation
figure27_slvsbno4.gif
V(IN) = 3.0 V bench power supply
Figure 66. Sampling Waveform
figure32_slvsbno4.gif
V(IN) = 4.0 V from bench power supply + additional CIN = 100 uF
R(OUT) = open - > 50 Ω
Figure 68. Load Transient Response
figure34_slvsbno4.gif
V(IN) = 4.0 V from bench power supply
VOUT resistors modified to provide 1.8 V
EN2 = high, EN1 transitioned high to low
Figure 70. Ship-Mode Startup Behavior