SNVS739F December   2011  – October 2016 LM10504

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 - General
    6. 6.6  Electrical Characteristics - Buck 1
    7. 6.7  Electrical Characteristics - Buck 2
    8. 6.8  Electrical Characteristics - Buck 3
    9. 6.9  Electrical Characteristics - LDO
    10. 6.10 Electrical Characteristics - Comparators
    11. 6.11 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Buck Regulators Description
      2. 7.3.2 PWM Operation
      3. 7.3.3 PFM Operation
      4. 7.3.4 Soft Start
      5. 7.3.5 Current Limiting
      6. 7.3.6 Internal Synchronous Rectification
      7. 7.3.7 Bypass-FET Operation on Buck 1 and Buck 2
      8. 7.3.8 Low Dropout Operation
      9. 7.3.9 Out of Regulation
    4. 7.4 Device Functional Modes
      1. 7.4.1  Start-Up Sequence
      2. 7.4.2  Power-On Default and Device Enable
      3. 7.4.3  Reset Pin Function
      4. 7.4.4  DevSLP Function
        1. 7.4.4.1 DevSLP Pin
        2. 7.4.4.2 DevSLP Programming Through SPI
        3. 7.4.4.3 DevSLP Operational Constraints
      5. 7.4.5  Vselect_B2, Vselect_B3 Function
      6. 7.4.6  Undervoltage Lockout (UVLO)
      7. 7.4.7  Overvoltage Lockout (OVLO)
      8. 7.4.8  Device Status, Interrupt Enable
      9. 7.4.9  Thermal Shutdown (TSD)
      10. 7.4.10 Comparator
    5. 7.5 Programming
    6. 7.6 Register Maps
  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 External Components Selection
          1. 8.2.2.1.1 Output Inductors and Capacitors Selection
          2. 8.2.2.1.2 Inductor Selection
            1. 8.2.2.1.2.1 Recommended Method for Inductor Selection
            2. 8.2.2.1.2.2 Alternate Method for Inductor Selection
              1. 8.2.2.1.2.2.1 Suggested Inductors and Their Suppliers
          3. 8.2.2.1.3 Output and Input Capacitors Characteristics
            1. 8.2.2.1.3.1 Output Capacitor Selection
            2. 8.2.2.1.3.2 Input Capacitor Selection
        2. 8.2.2.2 Recommendations For Unused Functions and Pins
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 PCB Layout Thermal Dissipation For DSGBA Package
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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発注情報

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 LM10504 contains three buck converters and one LDO.

8.2 Typical Application

LM10504 30176901.gif Figure 25. Typical Application Diagram

8.2.1 Design Requirements

Table 5 lists the output characteristics of the power regulators.

Table 5. Output Voltage Configurations for LM10504

REGULATOR VOUT IF
Vselect=HIGH
(B2, B3)
VOUT IF
Vselect=LOW
(B2, B3)
VOUT IF
DevSLP=HIGH
(DevSLP MODE)
VOUT MAXIMUM OUTPUT CURRENT TYPICAL APPLICATION COMMENTS
Buck 1 3 V 3 V Off 1.1 V to 3.6,
50 mV steps
1.6 A VCC Flash
Buck 2 3 V 1.8 V Off 1.1 V to 3.6,
50 mV steps
1 A VCCQ Interface
Buck 3 1.2 V 1 V Vnominal –7% 0.7 V to 1.335 V,
5 mV steps
1 A VCORE Core
LDO 3 V 3 V 3 V 3 V 250 mA VHOST controller Reference for host

8.2.2 Detailed Design Procedure

8.2.2.1 External Components Selection

All three switchers require an input capacitor and an output inductor-capacitor filter. These components are critical to the performance of the device. All three switchers are internally compensated and do not require external components to achieve stable operation. The output voltages of the bucks can be programmed through the SPI pins.

8.2.2.1.1 Output Inductors and Capacitors Selection

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

  • Load transient response
  • Stability
  • Efficiency
  • Output ripple voltage
  • Overcurrent ruggedness

The device has been optimized for use with nominal LC values as shown in Figure 25.

8.2.2.1.2 Inductor Selection

The recommended inductor values are shown in Figure 25. It is important to ensure the inductor core does not saturate during any foreseeable operational situation. The inductor must be rated to handle the peak load current plus the ripple current in Equation 2.

Care must 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 must be requested from the manufacturer.

Equation 2. LM10504 30176913.gif

The two methods of selecting the inductor saturation are in Recommended Method for Inductor Selection and Alternate Method for Inductor Selection.

8.2.2.1.2.1 Recommended Method for Inductor Selection

The best way to ensure the inductor does not saturate is to choose an inductor that has saturation current rating greater than the maximum device current limit, as specified in Electrical Characteristics – General. In this case, the device prevents inductor saturation by going into current limit before the saturation level is reached.

8.2.2.1.2.2 Alternate Method for Inductor Selection

If the recommended approach cannot be used, care must be taken to ensure that the saturation current is greater than the peak inductor current as calculated in Equation 3.

Equation 3. LM10504 30176914.gif

where

  • ISAT is the inductor saturation current at operating temperature
  • ILPEAK is the peak inductor current during worst case conditions
  • IOUTMAX is the maximum average inductor current
  • IRIPPLE is the peak-to-peak inductor current
  • VOUT is the output voltage
  • VIN is the input voltage
  • L is the inductor value in Henries at IOUTMAX
  • F is the switching frequency, Hertz
  • D is the estimated duty factor
  • EFF is the estimated power supply efficiency

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

8.2.2.1.2.2.1 Suggested Inductors and Their Suppliers

The designer must choose the inductors that best match the system requirements. A very wide range of inductors are available as regarding physical size, height, maximum current (thermally limited, and inductance loss limited), series resistance, maximum operating frequency, losses, and so forth. In general, smaller physical size inductors have higher series resistance (DCR), and implicitly lower overall efficiency is achieved. Very low-profile inductors may have even higher series resistance. The designer must try to find the best compromise between system performance and cost.

Table 6. Recommended Inductors

VALUE MANUFACTURER PART NUMBER DCR CURRENT PACKAGE
2.2 µH Murata LQH55PN2R2NR0L 31 mΩ 2.5 A 2220
2.2 µH TDK NLC565050T-2R2K-PF 60 mΩ 1.3 A 2220
2.2 µH Murata LQM2MPN2R2NG0 110 mΩ 1.2 A 806

8.2.2.1.3 Output and Input Capacitors Characteristics

Special attention must be paid when selecting these components. As shown in Figure 26, the DC bias of these capacitors can result in a capacitance value that falls below the minimum value given in Table 7. The graph shows the capacitance out of spec for the 0402 case size capacitor at higher bias voltages. TI recommends that the capacitor manufacturers’ specifications for the nominal value capacitor are consulted for all conditions, as some capacitor sizes (for example, 0402) may not be suitable in the actual application.

LM10504 30176915.gif Figure 26. Typical Variation in Capacitance vs DC Bias

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, only varies 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 changes 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 44 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 must also be noted that the ESR of a typical tantalum increases about 2:1 as the temperature goes from 25°C down to −30°C, so some guard band must be allowed.

8.2.2.1.3.1 Output Capacitor Selection

The output capacitor of a switching converter absorbs the AC ripple current from the inductor and provides the initial response to a load transient. The ripple voltage at the output of the converter is the product of the ripple current flowing through the output capacitor and the impedance of the capacitor. The impedance of the capacitor can be dominated by capacitive, resistive, or inductive elements within the capacitor, depending on the frequency of the ripple current. Ceramic capacitors have very low ESR and remain capacitive up to high frequencies. Their inductive component can usually be neglected at the frequency ranges at which the switcher operates.

LM10504 30176916.gif Figure 27. Basic Schematic of Feedback Components

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

Note that the output voltage ripple increases with the inductor current ripple and the Equivalent Series Resistance of the output capacitor (ESRCOUT). Also note that the actual value of the capacitor’s ESRCOUT is frequency and temperature dependent, as specified by its manufacturer. The ESR must be calculated at the applicable switching frequency and ambient temperature with Equation 4.

Equation 4. LM10504 30176917.gif

Output ripple can be estimated from the vector sum of the reactive (capacitance) voltage component and the real (ESR) voltage component of the output capacitor with Equation 5 and Equation 6.

Equation 5. LM10504 30176918.gif

where

Equation 6. LM10504 30176931.gif

where

  • VOUT-RIPPLE-PP is the estimated output ripple
  • VROUT is the estimated real output ripple
  • VCOUT is the estimated reactive output ripple

The device is designed to be used with ceramic capacitors on the outputs of the buck regulators. The recommended dielectric type of these capacitors is X5R, X7R, or of comparable material to maintain proper tolerances over voltage and temperature. The recommended value for the output capacitors is 22 μF, 6.3 V with an ESR of 2 mΩ or less. The output capacitors need to be mounted as close as possible to the output or ground pins of the device.

Table 7. Recommended Output Capacitors

MODEL TYPE VENDOR VENDOR VOLTAGE RATING CASE SIZE
08056D226MAT2A Ceramic, X5R AVX Corporation 6.3 V 0805, (2012)
C0805L226M9PACTU Ceramic, X5R Kemet 6.3 V 0805, (2012)
ECJ-2FB0J226M Ceramic, X5R Panasonic - ECG 6.3 V 0805, (2012)
JMK212BJ226MG-T Ceramic, X5R Taiyo Yuden 6.3 V 0603, (1608)
C2012X5R0J226M Ceramic, X5R TDK Corporation 6.3 V 0603, (1608)

8.2.2.1.3.2 Input Capacitor Selection

There are 3 buck regulators in the LM10504 device. Each of these buck regulators has its own input capacitor which must be located as close as possible to their corresponding SWx_VIN and SWx_GND pins, where x designates Buck 1, 2, or 3. The 3 buck regulators operate at 120° out of phase, which means that they switch on at equally spaced intervals, to reduce the input power rail ripple. TI recommends connecting all the supply and ground pins of the buck regulators, SWx_VIN to two solid internal planes located under the device. In this way, the 3 input capacitors work together and further reduce the input current ripple. A larger tantalum capacitor can also be located in the proximity of the device.

The input capacitor supplies the AC switching current drawn from the switching action of the internal power FETs. The input current of a buck converter is discontinuous, so the ripple current supplied by the input capacitor is large. The input capacitor must be rated to handle both the RMS current and the dissipated power.

The input capacitor must be rated to handle this current with Equation 7.

Equation 7. LM10504 30176921.gif

The power dissipated in the input capacitor is given by Equation 8.

Equation 8. LM10504 30176922.gif

The device is designed to be used with ceramic capacitors on the inputs of the buck regulators. The recommended dielectric type of these capacitors is X5R, X7R, or of comparable material to maintain proper tolerances over voltage and temperature. The minimum recommended value for the input capacitor is 10 µF with an ESR of 10 mΩ or less. The input capacitors need to be mounted as close as possible to the power and ground input pins of the device.

The input power source supplies the average current continuously. However, during the PFET switch on-time, 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 results in conservative estimates of input ripple voltage and capacitor RMS current.

Input ripple voltage is estimated with Equation 9.

Equation 9. LM10504 30176923.gif

where

  • VPPIN is the estimated peak-to-peak input ripple voltage
  • IOUT is the output current
  • CIN is the input capacitor value
  • ESRCIN is the input capacitor ESR

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 with Equation 10.

Equation 10. LM10504 30176924.gif

where

  • IRMSCIN is the estimated input capacitor RMS current

8.2.2.2 Recommendations For Unused Functions and Pins

If any function is not used in the end application, see Table 8 for tying off the associated pins on the circuit boards must be used.

Table 8. Unused Pin Recommendations

FUNCTION PIN IF UNUSED
BUCK1 VIN_B1 Connect to GND
SW_B1 Floating
FB_B1 Connect to GND
BUCK2 VIN_B2 Connect to GND
SW_B2 Floating
FB_B2 Connect to GND
BUCK3 VIN_B3 Connect to VIN
SW_B3 Floating
FB_B3 Connect to VIN
SPI SPI_CS Connect to VIN_IO
SPI_DI Connect to GND
SPI_DO Connect to GND
SPI_CK Connect to GND
Vselect_B2 Connect to GND or leave open
Vselect_B3 Connect to VIN or leave open
DevSLP Connect to GND or leave open
RESET Connect to VIN_IO
COMPARATOR VCOMP Connect to VIN
Interrupt Leave open

8.2.3 Application Curves

LM10504 30176957.gif Figure 28. LDO VOUT vs IOUT
LM10504 30176958.gif Figure 29. LDO VIN vs VOUT