SLTS278J November   2010  – March 2020 PTH08T250W

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1. Table 1. Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Electrical Characteristics
    3. 7.3 Typical Characteristics (VI = 12 V)
    4. 7.4 Typical Characteristics (VI = 5 V)
  8. 8 Detailed Description
    1. 8.1 Overview: TurboTrans™ Technology
    2. 8.2 Feature Description
      1. 8.2.1 Soft-Start Power-Up
      2. 8.2.2 Differential Output Voltage Remote Sense
      3. 8.2.3 Overcurrent Protection
      4. 8.2.4 Overtemperature Protection (OTP)
  9. 9 Application and Implementation
    1. 9.1 Typical Application
      1. 9.1.1 Detailed Design Procedure
        1. 9.1.1.1  Adjusting the Output Voltage
        2. 9.1.1.2  Capacitor Recommendations for the PTH08T250W Power Module
          1. 9.1.1.2.1 Capacitor Technologies
          2. 9.1.1.2.2 Input Capacitor (Required)
          3. 9.1.1.2.3 Input Capacitor Information
          4. 9.1.1.2.4 Output Capacitor (Required)
          5. 9.1.1.2.5 Output Capacitor Information
          6. 9.1.1.2.6 TurboTrans Output Capacitance
          7. 9.1.1.2.7 Non-TurboTrans Output Capacitance
          8. 9.1.1.2.8 Designing for Fast Load Transients
          9. 9.1.1.2.9 Capacitor Table
        3. 9.1.1.3  TurboTrans™ Technology
        4. 9.1.1.4  TurboTrans™ Selection
          1. 9.1.1.4.1 PTH08T250W Type B Capacitors
            1. 9.1.1.4.1.1 RTT Resistor Selection
          2. 9.1.1.4.2 PTH08T250W Type C Capacitors
            1. 9.1.1.4.2.1 RTT Resistor Selection
        5. 9.1.1.5  Undervoltage Lockout (UVLO)
          1. 9.1.1.5.1 UVLO Adjustment
        6. 9.1.1.6  On/Off Inhibit
        7. 9.1.1.7  Current Sharing
          1. 9.1.1.7.1 Current Sharing and TurboTrans
            1. 9.1.1.7.1.1 Current Sharing Thermal Derating Curves
            2. 9.1.1.7.1.2 Current Sharing Layout
        8. 9.1.1.8  Prebias Startup Capability
        9. 9.1.1.9  SmartSync Technology
        10. 9.1.1.10 Auto-Track™ Function
          1. 9.1.1.10.1 How Auto-Track™ Works
          2. 9.1.1.10.2 Typical Auto-Track Application
          3. 9.1.1.10.3 Notes on Use of Auto-Track™
  10. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  11. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape, Reel, and Tray Drawings

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9.1.1.1 Adjusting the Output Voltage

The Vo Adjust control sets the output voltage of the PTH08T250W. The adjustment range of the PTH08T250W is 0.7 V to 3.6 V. The adjustment method requires the addition of a single external resistor, RSET, that must be connected directly between pins Vo Adjust (pin 18) and AGND (pin 4). Table 2 gives the standard value of the external resistor for a number of standard voltages, along with the actual output voltage that this resistance value provides.

For other output voltages, the value of the required resistor can either be calculated using the following formula, or simply selected from the range of values given in Table 3. Figure 14 shows the placement of the required resistor.

Equation 1. PTH08T250W q_rset_lts278.gif

Table 2. Standard Values of RSET for Standard Output Voltages

VO (STANDARD) (V) RSET (STANDARD VALUE) (kΩ) VO (ACTUAL) (V)
3.3 1.62 3.298
2.5 5.23 2.498
2.0 9.76 1.997
1.8 12.7 1.798
1.5 19.6 1.508
1.2 35.7 1.199
1.0 (1) 63.4 1.001
0.7 (1) Open 0.700
(1) The maximum input voltage is limited to (VO × 12) or 14 V, whichever is less. The maximum allowable input voltage is a function of switching frequency, and may increase or decrease when the SmartSync feature is utilized. See the SmartSync section for further guidance.
PTH08T250W v07049_lts278.gif
1. RSET: Use a 0.05 W resistor with a tolerance of 1% and temperature stability of 100 ppm/°C (or better). Connect the resistor directly between pins 18 and 4, as close to the regulator as possible, using dedicated PCB traces.
2. Never connect capacitors from VO Adjust to either + Sense, GND, or VO. Any capacitance added to the VO Adjust pin affects the stability of the regulator.
Figure 14. VO Adjust Resistor Placement

Table 3. Output Voltage Set-Point Resistor Values

VO REQUIRED (V) RSET (kΩ) VO REQUIRED (V) RSET (kΩ) VO REQUIRED (V) RSET (kΩ)
0.70 (1) Open 1.50 19.6 2.60 4.64
0.75 (1) 412 1.60 16.9 2.70 4.02
0.80 (1) 205 1.70 14.7 2.80 3.57
0.85 (1) 133 1.80 12.7 2.90 3.09
0.90 (1) 97.6 1.90 11.0 3.00 2.67
0.95 (1) 78.7 2.00 9.76 3.10 2.26
1.00 (1) 63.4 2.10 8.66 3.20 1.96
1.10 (1) 46.4 2.20 7.50 3.30 1.62
1.20 35.7 2.30 6.65 3.40 1.30
1.30 28.7 2.40 5.90 3.50 1.02
1.40 23.7 2.50 5.23 3.60 0.768
(1) For output voltages less than 1.2 V, the output ripple may increase (up to 2X) when operating at input voltages greater than (VO × 12). Adjusting the switching frequency using the SmartSync feature may increase or decrease this ratio. See the SmartSync section for further guidance.