SNVSA58C January   2015  – November 2017 LM26480-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Tables
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions: Bucks
    4. 7.4  Thermal Information
    5. 7.5  General Electrical Characteristics
    6. 7.6  Low Dropout Regulators, LDO1 and LDO2
    7. 7.7  Buck Converters SW1, SW2
    8. 7.8  I/O Electrical Characteristics
    9. 7.9  Power-On Reset Threshold/Function (POR)
    10. 7.10 Typical Characteristics — LDO
    11. 7.11 Typical Characteristics — Buck 2.8 V to 5.5 V
    12. 7.12 Typical Characteristics — Bucks 1 and 2
    13. 7.13 Typical Characteristics — Buck 3.6 V
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 DC-DC Converters
        1. 8.3.1.1 Linear Low Dropout Regulators (LDOs)
          1. 8.3.1.1.1 No-Load Stability
        2. 8.3.1.2 SW1, SW2: Synchronous Step-Down Magnetic DC-DC Converters
          1. 8.3.1.2.1  Functional Description
          2. 8.3.1.2.2  Circuit Operation Description
          3. 8.3.1.2.3  PWM Operation
          4. 8.3.1.2.4  Internal Synchronous Rectification
          5. 8.3.1.2.5  Current Limiting
          6. 8.3.1.2.6  PFM Operation
          7. 8.3.1.2.7  SW1, SW2 Control
          8. 8.3.1.2.8  Shutdown Mode
          9. 8.3.1.2.9  Soft Start
          10. 8.3.1.2.10 Low Dropout Operation
          11. 8.3.1.2.11 Flexible Power-On Reset (Power Good with Delay)
          12. 8.3.1.2.12 Undervoltage Lockout
    4. 8.4 Device Functional Modes
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 External Component Selection
      2. 9.1.2 Feedback Resistors for LDOs
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 High VIN- High Load Operation
        2. 9.2.1.2 Junction Temperature
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Custom Design With WEBENCH® Tools
        2. 9.2.2.2 Output Inductors and Capacitors for SW1 AND SW2
          1. 9.2.2.2.1 Inductor Selection for SW1 and SW2
          2. 9.2.2.2.2 Suggested Inductors and Their Suppliers
        3. 9.2.2.3 Output Capacitor Selection for SW1 and SW2
        4. 9.2.2.4 Input Capacitor Selection for SW1 and SW2
        5. 9.2.2.5 LDO Capacitor Selection
          1. 9.2.2.5.1 Input Capacitor
          2. 9.2.2.5.2 Output Capacitor
          3. 9.2.2.5.3 Capacitor Characteristics
      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 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Custom Design With WEBENCH® Tools
      2. 12.2.2 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

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.

Application Information

External Component Selection

LM26480-Q1 30040410.gif Figure 25. LDO Block Diagram

Table 5. Buck External Component Selection

TARGET VOUT (V) IDEAL RESISTOR VALUES COMMON R VALUES ACTUAL VOUT w/ COM/R (V) ACTUAL VOUT DELTA FROM TARGET (V) FEEDBACK CAPACITORS POWER
RAIL
R1 (KΩ) R2 (KΩ) R1 (KΩ) R2 (KΩ) C1 (pF) C2 (pF)
0.8 120 200 121 200 0.803 0.002 15 none Buck1
0.9 160 200 162 200 0.905 0.005 15 none Only
1 200 200 200 200 1 0 15 none ^
1.1 240 200 240 200 1.1 0 15 none |
1.2 280 200 280 200 1.2 0 12 none |
1.3 320 200 324 200 1.31 0.01 12 none Buck1
1.4 360 200 357 200 1.393 -0.008 10 none And
1.5 400 200 402 200 1.505 0.005 10 none Buck2
1.6 440 200 442 200 1.605 0.005 8.2 none |
1.7 427 178 432 178 1.713 0.013 8.2 none |
1.8 463 178 464 178 1.803 0.003 8.2 none |
1.9 498 178 499 178 1.902 0.002 8.2 none |
2 450 150 453 150 2.01 0.01 8.2 none
2.1 480 150 475 150 2.083 -0.017 8.2 none ^
2.2 422 124 422 124 2.202 0.002 8.2 none |
2.3 446 124 442 124 2.282 -0.018 8.2 none |
2.4 471 124 475 124 2.415 0.015 8.2 none |
2.5 400 100 402 100 2.51 0.01 8.2 none |
2.6 420 100 422 100 2.61 0.01 8.2 none |
2.7 440 100 442 100 2.71 0.01 8.2 33 Buck2
2.8 460 100 464 100 2.82 0.02 8.2 33 Only
2.9 480 100 475 100 2.875 -0.025 8.2 33 |
3 500 100 499 100 2.995 -0.005 6.8 33 |
3.1 520 100 523 100 3.115 0.015 6.8 33 |
3.2 540 100 536 100 3.18 -0.02 6.8 33 |
3.3 560 100 562 100 3.31 0.01 6.8 33 |

The output voltages of the bucks of the LM26480-Q1 are established by the feedback resistor dividers R1 and R2 shown on the application circuit above. Equation 6 shows how to determine what value of V is:

Equation 6. VOUT = VFB (R1+R2)/R2

where

  • VFB is the voltage on the Buck FBx pin.

The Buck control loop will force the voltage on VFB to be 0.50 V ±3%.

Table 5 shows ideal resistor values to establish buck voltages from 0.8 V to 3.3 V along with common resistor values to establish these voltages. Common resistors do not always produce the target value, error is given in the delta column.

In addition to the resistor feedback, capacitor feedback C1 is always required, and depending on the output voltage capacitor C2 is also required.

INDUCTOR VALUE UNIT DESCRIPTION NOTES
LSW1,2 2.2 µH SW1,2 inductor DCR 70 mΩ

Feedback Resistors for LDOs

See Figure 25.

Table 6. LDO External Component Selection

TARGET VOUT (V) IDEAL RESISTOR VALUES COMMON R VALUES ACTUAl VOUT W/Com/R (V)
R1 (KΩ) R2 (KΩ) R1 (KΩ) R2 (KΩ)
1 200 200 200 200 1
1.1 240 200 240 200 1.1
1.2 280 200 280 200 1.2
1.3 320 200 324 200 1.31
1.4 360 200 357 200 1.393
1.5 400 200 402 200 1.505
1.6 440 200 442 200 1.605
1.7 480 200 562 232 1.711
1.8 520 200 604 232 1.802
1.9 560 200 562 200 1.905
2 600 200 604 200 2.01
2.1 640 200 715 221 2.118
2.2 680 200 681 200 2.203
2.3 720 200 806 226 2.283
2.4 760 200 845 221 2.412
2.5 800 200 750 187 2.505
2.6 840 200 909 215 2.614
2.7 880 200 1100 249 2.709
2.8 920 200 1150 249 2.809
2.9 960 200 1210 255 2.873
3 1000 200 1000 200 3
3.1 1040 200 1000 191 3.118
3.2 1080 200 1000 187 3.174
3.3 1120 200 1210 215 3.314
3.4 1160 200 1210 210 3.381
3.5 1200 200 1210 200 3.525

The output voltages of the LDOs of the LM26480-Q1 are established by the feedback resistor dividers R1 and R2 shown on Figure 25 above. Equation 7 shows calculation for VOUT:

Equation 7. VOUT = VFB(R1+R2)/R2

where

  • VFB is the voltage on the LDOX_FB pin.

The LDO control loop will force the voltage on VFB to be 0.50 V ±3%. The above table shows ideal resistor values to establish LDO voltages from 1 V to 3.5 V along with common resistor values to establish these voltages. Common resistors do not always produce the target value, error is given in the final column.

To keep the power consumed by the feedback network low it is recommended that R2 be established as about 200 kΩ. Lesser values of R2 are okay at the users discretion.

Typical Application

LM26480-Q1 typapp_snvs543.gif Figure 26. LM26480-Q1 Application Circuit

Design Requirements

High VIN- High Load Operation

Additional information is provided when the device is operated at extremes of VIN and regulator loads. These are described in terms of the junction temperature and buck output ripple management.

Junction Temperature

The maximum junction temperature TJ-MAX-OP of 125°C of the device package.

Equation 8 and Equation 9 demonstrate junction temperature determination, ambient temperature TA-MAX, and total chip power must be controlled to keep TJ below this maximum:

Equation 8. TJ-MAX-OP = TA-MAX + (RθJA) [°C/Watt] × (PD-MAX) [Watts]

Total IC power dissipation PD-MAX is the sum of the individual power dissipation of the four regulators plus a minor amount for chip overhead. Chip overhead is bias, TSD, and LDO analog.

Equation 9. LM26480-Q1 eq01_snvs543.gif

where

  • η is the efficiency for the specific condition is taken from efficiency graphs.

If VIN and ILOAD increase, the output ripple associated with the buck regulators also increases. This mainly occurs with VIN > 5.2 V and a load current greater than 1.2 A. To ensure operation in this area of operation, TI recommends that the system designer circumvents the output ripple issues by installing Schottky diodes on the bucks(s) that are expected to perform under these extreme conditions.

Detailed Design Procedure

Output Inductors and Capacitors for SW1 AND SW2

There are several design considerations related to the selection of output inductors and capacitors:

  • Load transient response;
  • Stability;
  • Efficiency;
  • Output ripple voltage; and
  • Overcurrent ruggedness.

The LM26480-Q1 has been optimized for use with nominal values 2.2 µH and 10 µF. If other values are needed for the design, please contact Texas Instruments sales with any concerns.

Inductor Selection for SW1 and SW2

TI recommends a nominal inductor value of 2.2 µH. It is important to ensure the inductor core does not saturate during any foreseeable operational situation.

Care should be taken when reviewing the different saturation current ratings that are specified by different manufacturers. Saturation current ratings are typically specified at 25°C, so ratings at maximum ambient temperature of the application should be requested from the manufacturer.

There are two methods to choose the inductor saturation current rating:

Recommended method:

The best way to ensure the inductor does not saturate is to choose an inductor that has saturation current rating greater than the maximum LM26480-Q1 current limit of 2.4 A. In this case the device prevents inductor saturation.

Alternate method:

If the recommended approach cannot be used, care must be taken to ensure that the saturation current is greater than the peak inductor current:

Equation 10. LM26480-Q1 30040471.gif

where

  • ISAT: Inductor saturation current at operating temperature
  • ILPEAK: Peak inductor current during worst case conditions
  • IOUTMAX: Maximum average inductor current
  • IRIPPLE: Peak-to-peak inductor current
  • VOUT: Output voltage
  • VIN: Input voltage
  • L: Inductor value in Henries at IOUTMAX
  • F: Switching frequency, Hertz
  • D: Estimated duty factor
  • EFF: Estimated power supply efficiency

ISAT may not be exceeded during any operation, including transients, start-up, high temperature, worst-case conditions, etc.

Suggested Inductors and Their Suppliers

MODEL MANUFACTURER DIMENSIONS (mm) DCR (max) (mΩ) ISATURATION (A)
(values approx.)
DO3314-222MX Coilcraft 3.3 × 3.3 × 1.4 200 1.8
LPO3310-222MX Coilcraft 3.3 × 3.3 × 1 150 1.3
ELL6PG2R2N Panasonic 6 × 6 × 2 37 2.2
ELC6GN2R2N Panasonic 6 × 6 × 1.5 53 1.9
CDRH2D14NP-2R2NC Sumida 3.2 × 3.2 × 1.5 94 1.5

Output Capacitor Selection for SW1 and SW2

TI recommends a ceramic output capacitor of 10 µF, 6.3 V with an ESR of less than 500 mΩ.

Output ripple can be estimated from the vector sum of the reactive (capacitor) voltage component and the real (ESR) voltage component of the output capacitor.

Equation 11. LM26480-Q1 30040429.gif

where

  • VCOUT: Estimated reactive output ripple
  • VROUT: Estimated real output ripple
  • VPPOUT: Estimated peak-to-peak output ripple

The output capacitor needs to be mounted as close as possible to the output pin of the device. For better temperature performance, X7R or X5R types are recommended. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603.

DC bias characteristics vary from manufacturer to manufacturer and by case size. DC bias curves should be requested from them as part of the capacitor selection process. ESR is typically higher for smaller packages.

The output filter capacitor smooths out current flow from the inductor to the load, helps maintain a steady output voltage during transient load changes and reduces output voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low ESR to perform these functions.

Note that the output voltage ripple is dependent on the inductor current ripple and the equivalent series resistance of the output capacitor (ESRCOUT). ESRCOUT is frequency dependent as well as temperature dependent. The RESR should be calculated with the applicable switching frequency and ambient temperature.

Input Capacitor Selection for SW1 and SW2

It is required to use a ceramic input capacitor of at least 4.7 μF and 6.3 V with an ESR of less than 500 mΩ.

The input power source supplies average current continuously. During the PFET switch on-time, however, the demanded di/dt is higher than can be typically supplied by the input power source. This delta is supplied by the input capacitor.

A simplified “worst case” assumption is that all of the PFET current is supplied by the input capacitor. This will result in conservative estimates of input ripple voltage and capacitor RMS current. Input ripple voltage is estimated in Equation 12:

Equation 12. LM26480-Q1 30040430.gif

where

  • VPPIN: Estimated peak-to-peak input ripple voltage
  • IOUT: Output current, Amps
  • CIN: Input capacitor value, Farads
  • ESRIN: Input capacitor ESR, Ohms

This capacitor is exposed to significant RMS current, so it is important to select a capacitor with an adequate RMS current rating. Capacitor RMS current estimated as follows:

Equation 13. LM26480-Q1 30040422.gif

where

  • IRSCIN: Estimated input capacitor RMS current

Table 7. Suggested Capacitors and Their Suppliers

MODEL TYPE VENDOR VOLTAGE RATING (V) CASE SIZE
4.7 µF for CIN
C2012X5R0J475K Ceramic, X5R TDK 6.3 0805, (2012)
JMK212BJ475K Ceramic, X5R Taiyo-Yuden 6.3 0805, (2012)
GRM21BR60J475K Ceramic, X5R Murata 6.3 0805, (2012)
C1608X5R0J475K Ceramic, X5R TDK 6.3 0603, (1608)
10 µF for COUT
GRM21BR60J106K Ceramic, X5R Murata 6.3 0805, (2012)
JMK212BJ106K Ceramic, X5R Taiyo-Yuden 6.3 0805, (2012)
C2012X5R0J106K Ceramic, X5R TDK 6.3 0805, (2012)
C1608X5R0J106K Ceramic, X5R TDK 6.3 0603, (1608)

LDO Capacitor Selection

Input Capacitor

An input capacitor is required for stability. TI recommends that a 1-μF capacitor be connected between the LDO input pin and ground (this capacitance value may be increased without limit). This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

CAUTION

Tantalum capacitors can suffer catastrophic failures due to surge currents when connected to a low impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be specified by the manufacturer to have a surge current rating sufficient for the application.

There are no requirements for the ESR on the input capacitor, but tolerance and temperature coefficient must be considered when selecting the capacitor to ensure the capacitance will remain approximately 1 μF over the entire operating temperature range.

Output Capacitor

The LDOs on the LM26480-Q1 are designed specifically to work with very small ceramic output capacitors. A 1-μF ceramic capacitor (temperature types Z5U, Y5V, or X7R) with ESR between 5 mΩ to 500 mΩ, are suitable in the application circuit. It is also possible to use tantalum or film capacitors at the device output COUT (or VOUT), but these are not as attractive for reasons of size and cost. The output capacitor must meet the requirement for the minimum value of capacitance and also have an ESR value that is within the range 5 mΩ to 500 mΩ for stability.

Capacitor Characteristics

The LDOs are designed to work with ceramic capacitors on the output to take advantage of the benefits they offer. For capacitance values in the range of 0.47 μF to 4.7 μF, ceramic capacitors are the smallest, least expensive and have the lowest ESR values, thus making them best for eliminating high frequency noise. The ESR of a typical 1-μF ceramic capacitor is in the range of 20 mΩ to 40 mΩ, which easily meets the ESR requirement for stability for the LDOs.

For both input and output capacitors, careful interpretation of the capacitor specification is required to ensure correct device operation. The capacitor value can change greatly, depending on the operating conditions and capacitor type.

In particular, the output capacitor selection should take account of all the capacitor parameters, to ensure that the specification is met within the application. The capacitance can vary with DC bias conditions as well as temperature and frequency of operation. Capacitor values will also show some decrease over time due to aging. The capacitor parameters are also dependent on the particular case size, with smaller sizes giving poorer performance figures in general. As an example, Figure 27 shows a typical graph comparing different capacitor case sizes in a capacitance vs. DC bias plot.

LM26480-Q1 30040416.gif Figure 27. Capacitance vs DC Bias

As shown in Figure 27, increasing the DC bias condition can result in the capacitance value that falls below the minimum value given in the recommended capacitor specifications table. Note that the graph shows the capacitance out of spec for the 0402 case size capacitor at higher bias voltages. It is therefore recommended that the capacitor manufacturers’ specifications for the nominal value capacitor are consulted for all conditions, as some capacitor sizes (such as 0402) may not be suitable in the actual application.

The ceramic capacitor’s capacitance can vary with temperature. The capacitor type X7R, which operates over a temperature range of −55°C to 125°C, will only vary the capacitance to within ±15%. The capacitor type X5R has a similar tolerance over a reduced temperature range of −55°C to 85°C. Many large value ceramic capacitors, larger than 1 μF are manufactured with Z5U or Y5V temperature characteristics. Their capacitance can drop by more than 50% as the temperature varies from 25°C to 85°C. Therefore X7R is recommended over Z5U and Y5V in applications where the ambient temperature will change significantly above or below 25°C.

Tantalum capacitors are less desirable than ceramic for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 0.47-μF to 4.7-μF range. Another important consideration is that tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical tantalum will increase about 2:1 as the temperature goes from 25°C down to −40°C, so some guard band must be allowed.

Table 8. Capacitor Characteristics

CAPACITOR MIN VALUE (µF) DESCRIPTION RECOMMENDED TYPE
CLDO1 0.47 LDO1 output capacitor Ceramic, 6.3V, X5R
CLDO2 0.47 LDO2 output capacitor
CSW1 10 SW1 output capacitor
CSW2 10 SW2 output capacitor

Application Curves

LM26480-Q1 30040441.png
VIN = 0 to 3.6 V VOUT = 2.5 V Load = 1 mA
Figure 28. Enable Start-Up Time (LDO1)
LM26480-Q1 30040460.png
VIN = 1.2 V Load = 1.5 A
Figure 30. Start-Up Into PWM Mode
LM26480-Q1 30040462.png
VIN = 1.2 V Load = 30 mA
Figure 32. Start-Up Into PFM Mode
LM26480-Q1 30040442.png
VIN = 0 to 3.6 V VOUT = 1.8 V Load = 1 mA
Figure 29. Enable Start-Up Time (LDO2)
LM26480-Q1 30040461.png
VIN = 3 V Load = 1.5 A
Figure 31. Start-Up Into PWM Mode
LM26480-Q1 30040470.png
VIN = 3 V Load = 30 mA
Figure 33. Start-Up Into PFM Mode