SNVS481M November   2006  – December 2015 LP3910

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
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics
    6. 7.6  Electrical Characteristics: I2C Interface
    7. 7.7  Electrical Characteristics: Li-Ion Battery Charger
    8. 7.8  Detection and Timing
    9. 7.9  Output Electrical Characteristics: CHG, STAT
    10. 7.10 Output Electrical Characteristics: NRST, IRQB, ONSTAT
    11. 7.11 Input Electrical Characteristics: USBSUSP, USBISEL
    12. 7.12 Input Electrical Characteristics: POWERACK, ONOFF, LDO2EN, BUCK1EN
    13. 7.13 Electrical Characteristics: LDO1 Low Dropout Linear Regulators
    14. 7.14 Electrical Characteristics: LDO2 Low Dropout Linear Regulator
    15. 7.15 Electrical Characteristics: Buck1 Converter
    16. 7.16 Electrical Characteristics: Buck2 Converter
    17. 7.17 Electrical Characteristics: Buck-Boost
    18. 7.18 Electrical Characteristics: ADC
    19. 7.19 I2C Timing Requirements
    20. 7.20 USB Timing Requirements
    21. 7.21 Typical Characteristics
      1. 7.21.1 Battery-Charger Characteristics
      2. 7.21.2 LDO Characteristics
      3. 7.21.3 Buck Characteristics
      4. 7.21.4 Buck-Boost Characteristics
  8. Detailed Description
    1. 8.1 Overview
      1. 8.1.1 Two Buck Converters
      2. 8.1.2 Buck-Boost Converter
      3. 8.1.3 LDO Regulators
      4. 8.1.4 Battery Charger
      5. 8.1.5 ADC
      6. 8.1.6 Supply Specification
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Buck1, Buck2: Synchronous Step-Down Magnetic DC-DC Converters
        1. 8.3.1.1 Buck1, Buck2 Operation
        2. 8.3.1.2 Circuit Operation Description
        3. 8.3.1.3 PWM Operation
        4. 8.3.1.4 Internal Synchronous Rectification
        5. 8.3.1.5 Current Limiting
        6. 8.3.1.6 PFM Operation
      2. 8.3.2  Buck-Boost: Synchronous Buck-Boost Magnetic DC-DC Converter
      3. 8.3.3  Linear Low Dropout Regulators (LDOs)
        1. 8.3.3.1 No-Load Stability
      4. 8.3.4  Li-Ion Linear Charger
        1. 8.3.4.1 Charger Architecture
        2. 8.3.4.2 Charge Status Indication
        3. 8.3.4.3 Thermal Charger Power FET Regulation
        4. 8.3.4.4 Battery Charger Operating Modes
          1. 8.3.4.4.1 Pre-Qualification Mode
          2. 8.3.4.4.2 Full-Rate Charging Mode
          3. 8.3.4.4.3 Constant-Voltage (CV) Charging Mode
          4. 8.3.4.4.4 Top-Off Charging Mode
          5. 8.3.4.4.5 Charge Cycle Complete
        5. 8.3.4.5 Battery Temperature Monitoring (TS Pin)
        6. 8.3.4.6 Disabling Charger
        7. 8.3.4.7 Safety Timer
        8. 8.3.4.8 Charging Maintenance
      5. 8.3.5  ADC
        1. 8.3.5.1 Battery Voltage Measurement
        2. 8.3.5.2 Battery Charge Current Measurement
        3. 8.3.5.3 External General-Purpose Sources
      6. 8.3.6  Interrupt Request Output
        1. 8.3.6.1 Interrupts and Standby Mode
        2. 8.3.6.2 Interrupt Sources
      7. 8.3.7  Power-On-Reset
      8. 8.3.8  Thermal Shutdown and Thermal Alarm
      9. 8.3.9  NRST Pin
      10. 8.3.10 Operation Without I2C Interface
      11. 8.3.11 I2C Master Power Concern
      12. 8.3.12 System Operation When the Load Current Exceeds the USB or Adapter Current Limit
      13. 8.3.13 Power Routing
      14. 8.3.14 Battery Monitor
      15. 8.3.15 External Power and Battery Detection
      16. 8.3.16 USB Suspend Mode
      17. 8.3.17 Setting the USB Current Limit
      18. 8.3.18 Control Registers
    4. 8.4 Device Functional Modes
      1. 8.4.1 State Machine Definitions
        1. 8.4.1.1 Power-Off Mode
        2. 8.4.1.2 Standby Mode
        3. 8.4.1.3 Active Mode
      2. 8.4.2 Mode Sequencing
        1. 8.4.2.1 Power-On, Power-Off Sequencing
        2. 8.4.2.2 Power-On Timing
        3. 8.4.2.3 Power-Off Timing
        4. 8.4.2.4 Transitioning From Standby to Active Mode (Power Up) Battery Power Present Only
        5. 8.4.2.5 Transitioning From Active Mode to Standby Mode
          1. 8.4.2.5.1 External Event Triggers the Transition From Active to Standby Mode
          2. 8.4.2.5.2 Transition From Active to Standby Mode Due to Expiring POWERACK Deadline
          3. 8.4.2.5.3 Transition From Charger Standby Mode to Either Active or Standby Mode
    5. 8.5 Programming
      1. 8.5.1 I2C-Compatible Serial Interface
        1. 8.5.1.1 I2C Signals
        2. 8.5.1.2 I2C Data Validity
        3. 8.5.1.3 I2C Start and Stop Conditions
        4. 8.5.1.4 Transferring Data
        5. 8.5.1.5 Register Write Cycle
        6. 8.5.1.6 Register Read Cycle
        7. 8.5.1.7 Multi-Byte I2C Command Sequence
    6. 8.6 Register Maps
      1. 8.6.1  LDO1 Control Register
      2. 8.6.2  BATTLOW Register (04)H Battery Low Alarm Register
      3. 8.6.3  PON Register (00)H Power-On Event Register
      4. 8.6.4  CHCTL Register (01)H Charger Control Register
      5. 8.6.5  CHSPV Register (02)H Charger Supervisor Register
      6. 8.6.6  ILIMIT Register (03)H Current Limit Register
      7. 8.6.7  ADCC Register (0a)H ADC Control Register
      8. 8.6.8  ADCD Register (0b)H ADC Output Data Register
      9. 8.6.9  IMR Register (0c)H Interrupt Mask Register
      10. 8.6.10 IRQ Register (0d)H Interrupt Request Register
      11. 8.6.11 LDO1 Control Register (08)H
      12. 8.6.12 LDO2 Control Register
      13. 8.6.13 Buck1, Buck2 Control Registers and BUCK1EN Pin
      14. 8.6.14 Buck-Boost Control Register
  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 Inductors for Buck1, Buck2 and Buck-Boost
          1. 9.2.2.1.1 Method 1
          2. 9.2.2.1.2 Method 2
        2. 9.2.2.2 External Capacitors
          1. 9.2.2.2.1 LDO Capacitor Selection
            1. 9.2.2.2.1.1 Input Capacitor
            2. 9.2.2.2.1.2 Output Capacitor
            3. 9.2.2.2.1.3 Capacitor Characteristics
            4. 9.2.2.2.1.4 Noise Bypass Capacitors for VREFH Pin
          2. 9.2.2.2.2 Buck1, Buck2 and Buck-Boost Capacitor Selection
            1. 9.2.2.2.2.1 Input Capacitor Selection for Buck1, Buck2 and Buck-Boost
            2. 9.2.2.2.2.2 Output Capacitor Selection for Buck1, Buck2 and Buck-Boost
        3. 9.2.2.3 Schottky Diode on Charger Input CHG_IN
        4. 9.2.2.4 Resistors
          1. 9.2.2.4.1 Battery Thermistor
          2. 9.2.2.4.2 I2C Pullup Resistors
          3. 9.2.2.4.3 RIREF Resistor
          4. 9.2.2.4.4 RISENSE Resistor
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 LDO Regulators
      2. 11.1.2 Buck and Buck-Boost Regulators
    2. 11.2 Layout Example
    3. 11.3 Thermal Performance of the WQFN Package
  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 Related Documentation
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

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 LP3910 is a programmable system power management unit optimized for HDD-based portable media players. The device is intended to connect to an AC-DC wall adapter or USB power source in addition to a lithium-Ion or lithium-polymer single-cell battery. The device can be configured over an I2C interface, or the default configuration stored in EPROM can be used. Additional features such as current and voltage measurements with the ADC or battery thermal monitoring can also be controlled via the I2C interface and interrupt pins.

9.2 Typical Application

LP3910 typapp_snvs481.gif Figure 75. LP3910 Typical Application

9.2.1 Design Requirements

For typical PMU applications, use the parameters listed in Table 15.

Table 15. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Minimum input voltage 2.7 V
Maximum input voltage 5.5 V
LDO1 output voltage 2.5 V
LDO2 output voltage 3 V
Buck1 output voltage 1.6 V
Buck2 output voltage 1.8 V
Buck-Boost output voltage 3.3 V
Charge current 100 mA

9.2.2 Detailed Design Procedure

9.2.2.1 Inductors for Buck1, Buck2 and Buck-Boost

There are two main considerations when choosing an inductor; the inductor must not saturate and the inductor current ripple is small enough to achieve the desired output voltage ripple. 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.

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

9.2.2.1.1 Method 1

The saturation current is greater than the sum of the maximum load current and the worst-case average-to-peak inductor current. This can be written as Equation 4:

Equation 4. LP3910 eq01_snvs481.gif

Considered when using the Buck-Boost in boost mode, use Equation 5:

Equation 5. LP3910 eq02_snvs481.gif

where

  • IRIPPLE: Average-to-peak inductor current
  • IOUTMAX: Maximum load current
  • VIN: Maximum input voltage in application
  • L: Minimum inductor value including worst case tolerances (30% drop can be considered for Method 1)
  • ƒ: Minimum switching frequency
  • VOUT: Output voltage

9.2.2.1.2 Method 2

A more conservative and recommended approach is to choose an inductor that has saturation current rating greater than the maximum current limit.

INDUCTOR VALUE DESCRIPTION NOTES
LSW1,2 2.2 µH Buck1,2 Inductor DCR 70 mΩ
LBB 2.2 µH Buck-Boost Inductor DCR 70 mΩ

9.2.2.2 External Capacitors

The regulators on the LP3910 require external capacitors for regulator stability. These are specifically designed for portable applications requiring minimum board space and smallest components. These capacitors must be correctly selected for good performance.

9.2.2.2.1 LDO Capacitor Selection

9.2.2.2.1.1 Input Capacitor

An input capacitor is required for stability. It is recommended that a 1-µF capacitor be connected between the LDO input pin and ground. (This capacitance value may be increased without limit.)

The input 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.

NOTE

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

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

9.2.2.2.1.2 Output Capacitor

The LDOs on the LP3910 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.

Tantalum or film capacitors may also be used 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.

9.2.2.2.1.3 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 must 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 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 76 shows a typical graph comparing different capacitor case sizes.

LP3910 20207623.gif Figure 76. Typical Variation in Capacitance vs DC Bias

As shown in Figure 76, 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 Figure 76 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 (for example, 0402) may not be suitable in the actual application.

Capacitance of a ceramic capacitor 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 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. The ESR of a typical tantalum increases about 2:1 as the temperature goes from +25°C down to −40°C, so some guard band must be allowed.

9.2.2.2.1.4 Noise Bypass Capacitors for VREFH Pin

Connecting respectively 100 nF and 1 nF grounded bypass capacitors to the VREFH pin significantly reduces noise on the LDO outputs. VREFH is a high-impedance node connected to a bandgap reference used for the LDOs. Any significant loading on this node causes a change on the regulated output voltages. For this reason, DC leakage current through these pins must be kept as low as possible for best output voltage accuracy. The types of capacitors best suited for the noise bypass capacitors are ceramic and film capacitors. High-quality ceramic capacitors with either NPI or COG dielectric typically have very low leakage. Polypropylene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current. Residual solder flux is another potential source of leakage, which mandates thorough cleaning of the assembled PCBs.

9.2.2.2.2 Buck1, Buck2 and Buck-Boost Capacitor Selection

9.2.2.2.2.1 Input Capacitor Selection for Buck1, Buck2 and Buck-Boost

A ceramic input capacitor of 10 μF, 6.3 V is sufficient for the magnetic DC-DC converters. Place the input capacitor as close as possible to the input of the device. A large value may be used for improved input voltage filtering. The recommended capacitor types are X7R or X5R. Y5V-type capacitors must not be used. DC bias characteristics of ceramic capacitors must be considered when selecting case sizes like 0805 and 0603. The input filter capacitor supplies current to the PFET switch of the DC-DC converter in the first half of each cycle and reduces voltage ripple imposed on the input power source. Low ESR in a ceramic capacitor provides the best noise filtering of the input voltage spikes due to fast current transients. A capacitor with sufficient ripple current rating must be selected. The Input current ripple can be calculated as:

Equation 6. LP3910 20212336.gif

The worse case is when VIN = 2 × VOUT.

9.2.2.2.2.2 Output Capacitor Selection for Buck1, Buck2 and Buck-Boost

A 10-μF, 6.3-V ceramic capacitor must be used on the output of the Buck1 and Buck2 magnetic DC-DC converters. The buck-boost needs a 22-μF capacitor. The output capacitor must be mounted as close as possible to the output of the device. A large value may be used for improved input voltage filtering. The recommended capacitor types are X7R or X5R. Y5V-type capacitors should not be used. 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 DC bias curves should be requested from them and analyzed as part of the capacitor selection process.

The output filter capacitor of the magnetic DC-DC converter 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 ESD to perform these functions.

The output voltage ripple is caused by the charging and the discharging of the output capacitor and also due to its ESR and can be calculated using Equation 7:

Equation 7. LP3910 20207626.gif

Voltage peak-to-peak ripple due to ESR can be expressed by Equation 8:

Equation 8. VPP-ESR = 2 × IRIPPLE × RESR

Because the VPP-C and VPP-ESR are out of phase, the RMS value can be used to get an approximate value of the peak-to-peak ripple:

Equation 9. LP3910 20207627.gif

The output voltage ripple is dependent on the inductor current ripple and the ESR of the output capacitor (RESR). The RESR is frequency dependent as well as temperature dependent. The RESR must be calculated with the applicable switching frequency and ambient temperature.

Table 16. Recommended Capacitors

CAPACITOR MINIMUM VALUE (µF) DESCRIPTION RECOMMENDED TYPE
CVDD 4.7 Charger input capacitor Ceramic, 6.3 V, X5R
CCHG_DET 4.7 Charger input capacitor Ceramic, 6.3 V, X5R
CUSB 4.7 USB power (VBUS) capacitor Ceramic, 6.3 V, X5R
CBATT 4.7 Li-ion battery capacitor Ceramic, 6.3 V, X5R
CLDO1 1 LDO output capacitor Ceramic, 6.3 V, X5R
CLDO2 1 LDO output capacitor Ceramic, 6.3 V, X5R
CVREFH 0.1 Bypass capacitor for internal voltage reference Ceramic, PolyPropylene and Polycarbonate Film
CVIN2,3 10 Buck1, Buck2 input capacitor Ceramic, 6.3 V, X5R
CVBUCK1,2 10 BUCK1,2 output capacitor Ceramic, 6.3 V, X5R
CBB 22 Buck-Boost output capacitor Ceramic, 6.3 V, X5R
CVIN1 1 LDO bypass capacitor Ceramic, 6.3 V, X5R
CVIN4 10 Buck and Buck-Boost bypass capacitor Ceramic, 6.3 V, X5R

9.2.2.3 Schottky Diode on Charger Input CHG_IN

A Schottky diode is required in the external adapter path to block the reverse current from either the USB or the battery source. The most critical parameter in the selection of the right Schottky diode is the leakage current, which must be below 10 µA over the temperature range in order to prevent false detection of the presence of an external adapter. In addition the Schottky diode must have a maximum voltage rating of 10 V or higher. The current rating depends on the current limit of the adapter. The forward voltage must be limited to 500 mV at its maximum current. The recommended Schottky diode is MBRA210ET3 from ON Semiconductor, which has a reverse leakage current under 1 µA at room temperature and a forward voltage drop of 500 mV at the maximum rated current (IF = 2 A).

9.2.2.4 Resistors

9.2.2.4.1 Battery Thermistor

The LP3910 battery thermistor bias provided by the TS pin is tailored to thermistors with the following specification:

  • Negative temperature coefficient
  • 100-kΩ resistance

A suitable solution is available from AVX thermistors:

AVXNB21250104 http://www.avxcorp.com/docs/Catalogs/nb21-23.pdf

9.2.2.4.2 I2C Pullup Resistors

I2C_SDA and I2C_SCL pins must have pullup resistors connected to the VDDIO pin. VDDIO must be connected to a power supply that is less than or equal to VDD, such as BUCK2. The values of the pullup resistors (typical approximately 1.8 kΩ) are determined by the capacitance of the bus. A resistor that is too large, combined with a given bus capacitance, results in a rise time that would violate the maximum rise time specification. A resistor that is too small results in a contention with the pulldown transistor on either slave(s) or master.

9.2.2.4.3 RIREF Resistor

The current through this resistor is used as a reference current that biases many analog circuits inside the LP3910 and must have a resistance of 121 kΩ ±1%.

9.2.2.4.4 RISENSE Resistor

The current through this resistor is used as a reference current for the charge current. The accuracy of the ADC is dependent on the tolerance of this resistor. RISENSE must have a resistance of 4.64 kΩ ±1% tolerance.

9.2.3 Application Curves

LP3910 202123101.png
Ch1 = Charge Current (mA) Ch4 = USBPWR (V)
Ch3 = CHG_DET (V)
Figure 77. Wall Adapter Removal With USBPWR Present
LP3910 20212353.png
VIN = 0 to 3.6 V VOUT = 1.8 V Load = 1 mA
Figure 79. Enable Start-Up Time (LDO2)
LP3910 20212363.gif
VOUT = 3.3 V L = 2.2 µH Forced PWM Mode
Figure 81. Buck2 Efficiency vs Output Current
LP3910 20212365.gif
VOUT = 3.3 V L = 2.2 μH PFM-to-PWM Mode
Figure 83. Buck2 Efficiency vs Output Current
LP3910 20212352.png
VIN = 0 to 3.6 V VOUT = 3.3 V Load = 1 mA
Figure 78. Enable Startup Time (LDO1)
LP3910 20212362.gif
VOUT = 1.8 V L = 2.2 µH Forced PWM Mode
Figure 80. Buck2 Efficiency vs Output Current
LP3910 20212364.gif
VOUT = 1.8 V L = 2.2 µH PFM-to-PWM Mode
Figure 82. Buck2 Efficiency vs Output Current