SNVSAF5D January   2016  – May 2021 TPS61194

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 (1) (1)
    6. 6.6  Internal LDO Electrical Characteristics
    7. 6.7  Protection Electrical Characteristics
    8. 6.8  Current Sinks Electrical Characteristics
    9. 6.9  PWM Brightness Control Electrical Characteristics
    10. 6.10 Boost and SEPIC Converter Characteristics
    11. 6.11 Logic Interface Characteristics
    12. 6.12 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 Integrated DC-DC Converter
      2. 7.3.2 Internal LDO
      3. 7.3.3 LED Current Sinks
        1. 7.3.3.1 Output Configuration
        2. 7.3.3.2 Current Setting
        3. 7.3.3.3 Brightness Control
      4. 7.3.4 Protection and Fault Detections
        1. 7.3.4.1 Adaptive DC-DC Voltage Control and Functionality of LED Fault Comparators
        2. 7.3.4.2 Overview of the Fault/Protection Schemes
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device States
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Application for 4 LED Strings
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Inductor Selection
          2. 8.2.1.2.2 Output Capacitor Selection
          3. 8.2.1.2.3 Input Capacitor Selection
          4. 8.2.1.2.4 LDO Output Capacitor
          5. 8.2.1.2.5 Diode
        3. 8.2.1.3 Application Curves
      2. 8.2.2 SEPIC Mode Application
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Inductor
          2. 8.2.2.2.2 Diode
          3. 8.2.2.2.3 Capacitor C1
        3. 8.2.2.3 Application Curves
  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 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.1 Integrated DC-DC Converter

The TPS61194 DC-DC converter generates supply voltage for the LEDs and can operate in boost mode or in SEPIC mode. The maximum output voltage VOUT_MAX is defined by an external resistive divider (R1, R2).

VOUT_MAX voltage should be chosen based on the maximum voltage required for LED strings. Recommended maximum voltage is about 30% higher than maximum LED string voltage. DC-DC output voltage is adjusted automatically based on LED current sink headroom voltage. Maximum, minimum, and initial boost voltages can be calculated with Equation 1:

Equation 1. GUID-7347474F-8207-4CC7-87E8-16DB73177939-low.gif

where

  • VBG = 1.2 V
  • R2 recommended value is 130 kΩ
  • Resistor values are in kΩ
  • K = 1 for maximum adaptive boost voltage (typical)
  • K = 0 for minimum adaptive boost voltage (typical)
  • K = 0.88 for initial boost voltage (typical)
GUID-72E43A65-F1F1-4BE6-BE10-D690D02F50E6-low.pngFigure 7-1 Maximum Converter Output Voltage vs R1 Resistance

Alternatively, a T-divider can be used if resistance less than 100 kΩ is required for the external resistive divider. Refer to Using the TPS61194xEVM Evaluation Module for details.

The converter is a current mode DC-DC converter, where the inductor current is measured and controlled with the feedback. Switching frequency is adjustable between 250 kHz and 2.2 MHz with RFSET resistor as Equation 2:

Equation 2. ƒSW = 67600 / (RFSET + 6.4)

where

  • ƒSW is switching frequency, kHz
  • RFSET is frequency setting resistor, kΩ

In most cases lower frequency has higher system efficiency. DC-DC internal parameters are chosen automatically according to the selected switching frequency (see Table 7-2) to ensure stability. In boost mode a 15-pF capacitor CFB must be placed across resistor R1 when operating in 300-kHz to 500-kHz range (see Typical Application for 4 LED Strings). When operating in the 1.8-MHz to 2.2-MHz range CFB = 4.7 pF.

GUID-C806EEE7-4041-453B-82AB-3AFB9AC90AA3-low.gifFigure 7-2 Boost Block Diagram

DC-DC can be driven by an external SYNC signal between 300 kHz and 2.2 MHz. If the external synchronization input disappears, DC-DC continues operation at the frequency defined by RFSET resistor. When external frequency disappears and SYNC pin level is low, converter continues operation without spread spectrum immediately. If SYNC remains high, converter continues switching with spread spectrum enabled after 256 µs.

External SYNC frequency must be 1.2 to 1.5 times higher than the frequency defined by RFSET resistor. Minimum frequency setting with RFSET is 250 kHz to support 300-kHz switching with external clock.

The optional spread spectrum feature (±3% from central frequency, 1-kHz modulation frequency) reduces EMI noise at the switching frequency and its harmonic frequencies. When external synchronization is used, spread spectrum is not available.

Table 7-1 DC-DC Synchronization Mode
SYNC PIN INPUTMODE
LowSpread spectrum disabled
HighSpread spectrum enabled
300 to 2200 kHz frequencySpread spectrum disabled, external synchronization mode
Table 7-2 DC-DC Parameters(1)
RANGEFREQUENCY (kHz)TYPICAL
INDUCTANCE (µH)		TYPICAL BOOST INPUT
AND OUTPUT CAPACITORS (µF)		MINIMUM SWITCH
OFF TIME (ns)(2)		BLANK
TIME (ns)		CURRENT
RAMP (A/s)		CURRENT RAMP
DELAY (ns)
1300 to 480332 ×10 (cer.) + 33 (electr.)1509524550
2480 to 11501510 (cer.) + 33 (electr.)609543300
31150 to 1650103 × 10 (cer.)4095790
41650 to 22004.73 × 10 (cer.)40701450
(1) Parameters are for reference only.
(2) Due to current sensing comparator delay the actual minimum off time is 6 ns (typical) longer than in the table.

The converter SW pin DC current is limited to 2 A (typical). To support short-term transient condition the current limit is automatically increased to 2.5 A for a short period of 1.5 seconds when a 2-A limit is reached.

Note:

Application condition where the 2-A limit is exceeded continuously is not allowed. In this case the current limit would be 2 A for 1.5 seconds followed by 2.5-A limit for 1.5 seconds, and this 3-second period repeats.

To keep switching voltage within safe levels there is a 48-V limit comparator in the event that FB loop is broken.