LM5118 Quick Start Component Calculator

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LM5118 Quick Start Component Calculator Powered By Docstoc
					LM5118 Quick Start Component Calculator
Note: The components calculated in this worksheet are reasonable starting values for a design
using the LM5118. They are not optimized for any particular performance attribute.                                                Operational Modes vs VIN
Step 1 - Application Requirements
                                                                                                                   45
                                                                                Vout (V)    12
Enter design requirements in the shaded cells                               Vin(min) (V)     5                     40
                                                                           Vin(max) (V)     40
                                               Maximum Average Load Current Iout (A)         3                     35
                                     Ripple Current as % of Maximum Load Current (%)       40%
                                                                       VCCX Voltage (V)      0                     30                                                                    Buck

                                      Vin at start of Transition to Buck-Boost Mode (V)    15.96                                                                                         Transition




                                                                                                     VIN (Volts)
                                                            Buck-Boost Mode Operation      YES                     25                                                                    Buck-boost

                                                                                                                   20
                                                           Recommended Controller IC       LM5118
                                                                                                                   15
Step 2 - Switching Frequency
                                          Maximum Possible Switching Frequency (kHz)        500                    10
                                                           Switching Frequency (kHz)        300
                                                             Timing Resistor, Rt (kW)      18.31                    5

Step 3 - Inductor Value                                                                                             0
                                         Calculated Buck Mode Inductor Value, Lb (µH)      23.33
                                 Calculated Buck-Boost Mode Inductor Value, Lb-b (µH)       9.80
                                                  Actual Chosen Inductor Value, L (µH)       10
                                                                                                              Vin
Step 4 - Calculate Output and Inductor Currents Based on Chosen Inductor
                                         Buck-Boost Ripple Current at Vin=Vout, ΔI (A)      2.00                                                                        VIN              VCC                7.79774309
                                                                                                                                                                                                             Cvcc
                                          Buck mode Ripple Current at Vin(max), ΔI (A)      2.80                         Ruv1                         CIN                                   HB
                                          Buck-Boost Ripple Current at Vin(min), ΔI (A)     1.18                   EN
                                           Buck-Mode Peak Inductor Current, Ip(b) (A)       4.40                                                                        EN                            Chb
                                   Buck-Boost Mode Peak Inductor Current, Ip(b-b) (A)      10.79
                                                                                                                                                                        UVLO                HO
Step 5 - Current Limit With Safety Margin; Recalculate Currents                                                                                                                                                                                                  Vou
                                        Current Limit Margin (% beyond Max Load) (%)       20%                          Cr                                              SS                  HS
                                                                                                                                        Ruv2
                                                      Current Sense Resistor, Rs (mW)      18.54                                                                                                                                 L
                                                      Closest Standard Value, Rs (mW)       15.0                                                      To VCC     Css          LM5118
                                           Buck Mode Average Output Current Limit (A)       6.93                                                                                            CS
                                                                                                      SYNC                                                                                                                                                COUT
                             Buck-Boost Mode Inductor Current Peak at Current Limit (A)    16.67
                                                                                                                                                                        SYNC                                          RS
                                    Buck-Boost Mode Average Output Current Limit (A)        4.73
                                                                                                                                                                        RT               CSG
Step 5 - Ramp Capacitor
                                                                            Cramp (pF)      333                              RT                             Rramp
                                                                            Rramp (kW)      NA                                                                                              LO
                                                                                                                                                                                                                                                                  R
                                                                                                                                                                        RAMP
Step 9 - Output Capacitors (Based on Worst Case Conditions for Each Mode)                                                                                                                   FB
                                                                                                                                        Cramp
                                                           Target output ripple (mV)        100
                                               Buck-Boost Duty cycle at Vin(min) (%)       71%
                                                                                                            Optional                                                                                      Czero Rcomp                                            Rf
                                    Buck-Boost RMS Ripple Current in Output Cap (A)         3.20            External                                                    VCCX           COMP
                                         Minimum COUT output Capacitor Value (µF)          70.59             Bias
                                                         Required COUT ESR (mW)             9.27                                                                        PGND
                                           Chosen COUT output capacitor value (µF)          300
                                             Buck Mode Output Ripple Voltage (mV)           18.5                                                                                                             Cpole
                                                                                                                                                                        AGND

Step 10 - Input Capacitors (Based on Worst Case Conditions for Each Mode)
                                            Buck-Boost RMS Input Ripple Current (A)         4.66
                         Buck-Boost Mode Peak to Peak Current Ripple in Input Cap (A)      10.20
                                             Buck Mode RMS input Ripple Current (A)         1.37
                               Buck Mode Peak to Peak Current Ripple in Input Cap (A)       7.20
                                                     Initial Input Capacitor Value(μF)     27.78
                                              Chosen CIN Input Capacitor Value (µF)          50

Step 10 - Feedback Resistors
                                                                               Rfb1 (W)    300.00
                                                                               Rfb2 (W)    2,626.8

Step 11 - Chb & Cvcc Capacitor
                                              High-side MOSFET Qg at VGS=10V (nC)          30.00
                                                 Minimum Bootstrap Capacitor Chb (µF)       0.08                                                                    Overall Gain and Phase
                                                           Chosen Value for Chb (µF)        0.1
                                             Minimum VCC Bypass Capacitor Cvcc (µF)           1
                                                                                                                                                100                                                                         180
Step 12 - Error Amplifier Compensation
                                                 Right Half Plane Zero Frequency (kHz)       7.81                                               80                                                                          150
                                                                                                                                                                                                                                     Phase Margin (Deg)




                                                                       Bandwidth (kHz)       2.05
                                                                    Modulator Gm (A/V)       6.18                                               60                                                                          120
                                                                                                                                    Gain (dB)




                                                 Modulator Gain at Loop Crossover (dB)      -7.80
                                                                                                                                                40                                                                          90
                                                 Target Error Amp Zero Frequency (Hz)        226
                                                  Tartet Error Amp Pole Frequency (Hz)     7,806                                                20                                                                          60
                                                                            Rcomp (W)      6,758
                                                                            Cpole (nF)       0.07                                                0                                                                          30
                                                                            Czero (nF)     104.09
                                                                                                                                                -20                                                                         0
Step 13 - Soft Start capacitor                                                                                                                    1.E+00       1.E+01    1.E+02    1.E+03        1.E+04      1.E+05    1.E+06
                                                            Choose soft-start time (ms)      12
                                                                                                                                                                                  Frequency (Hz)
                                                         Soft Start Capacitor Value (nF)    97.6

Step 14 - UVLO Threshold and Hiccup Mode Restart
                                              Minimum Value of Resistor Ruv1 (kW)            40
                                                         Chosen Value of Ruv1 (kW)           75
                                                 Desired Undervoltage Threshold (V)           4
                                                                    Ruv2 Value (kW)        29.33
                                            Choose off-time of hiccup duty cycle (µs)      1000
                                   Vin voltage for desired hiccup mode off-time (V)          12
                                      Hiccup Mode Off-time Capacitor Value Cr (µF)          0.10
LM5118 List of Components

   Component     Description                    Value
      Cin        Input capacitor                50 μF
     Cramp       Ramp capacitor                333 pF
      Css        Soft start capacitor          97.6 nF
      Cout       Output capacitor              300 μF
       Cr        UVLO filter capacitor         0.10 μF
     Cpole       Compensation capacitor         0.1 nF
     Czero       Compensation capacitor       104.1 nF
      Cvcc       VCC bypass capacitor          1.0 μF
      Chb        HB-SW bypass capacitor        0.10 μF
      Rfb1       Feedback resistor              300 Ω
      Rfb2       Feedback resistor            2,627 Ω
      Ruv1       UVLO divider resistor        75.0 kΩ
      Ruv2       UVLO divider resistor        29.3 kΩ
       Rs        Sense resistor               18.5 mΩ
       Rt        Oscillator timing resistor   18.31 kΩ
       L         Inductor                     10.0 μH
     Rramp       Optional ramp resistor           NA
     Rcomp       Compensation resistor         6.8 kΩ
Rating
 100V, X7R
100V, COG
 100V, X7R
  16V, X7R
 100V, X7R
 100V COG
 100V COG
 25V, X7R
 100V, X7R
   1/16 W
   1/16 W
   1/16 W
   1/16 W
     2W
   1/16 W
     13A
      -
   1/16 W
                                                             Error     Error      Overall
                     Modulator              Modulator       Amplifier Amplifier    Loop                    Loop
Frequency Frequency      Gain                 Phase          Gain      Phase       Gain                    Phase
    (Hz)   (rad/sec)     (dB)                  (deg)          (dB)     (deg)       (dB)                    (deg)
 1.00E-01  6.28E-01    11.4110              -2.60E-02        75.30       90        86.71                     90
 2.00E-01  1.26E+00    11.4110              -5.19E-02        69.28       90        80.69                     90
 5.00E-01  3.14E+00    11.4110              -1.30E-01        61.32       90        72.73                     90
 1.00E+00  6.28E+00    11.4110              -2.60E-01        55.30       90        66.71                     90
 2.00E+00  1.26E+01    11.4107              -5.19E-01        49.28       91        60.69                     90
 5.00E+00  3.14E+01    11.4089              -1.30E+00        41.32       91        52.73                     90
 1.00E+01  6.28E+01    11.4026              -2.59E+00        35.31       93        46.71                     90
 2.00E+01  1.26E+02    11.3773              -5.18E+00        29.31       95        40.69                     90
 5.00E+01  3.14E+02    11.2041              -1.28E+01        21.53      103        32.73                     90
 1.00E+02  6.28E+02    10.6368              -2.45E+01        16.07      114        26.71                     89
 2.00E+02  1.26E+03     8.9063              -4.27E+01        11.79      132        20.69                     89
 5.00E+02  3.14E+03     3.7326              -6.88E+01         9.02      156        12.75                     87
 1.00E+03  6.28E+03    -1.6419              -8.36E+01         8.42      168         6.78                     84
 2.00E+03  1.26E+04    -7.2913              -9.59E+01         8.26      174         0.97                     78
 5.00E+03  3.14E+04   -13.9580              -1.15E+02         8.22      177        -5.74                     62
 1.00E+04  6.28E+04   -17.1480              -1.31E+02         8.21      178        -8.94                     47
 2.00E+04  1.26E+05   -18.2260              -1.39E+02         8.19      177       -10.03                     38
 5.00E+04  3.14E+05   -16.7736              -1.30E+02         8.10      172        -8.67                     42
 1.00E+05  6.28E+05   -13.2371              -1.15E+02         7.81      164        -5.43                     48
 2.00E+05  1.26E+06    -8.1249              -1.04E+02         6.79      149        -1.33                     45
 5.00E+05  3.14E+06    -0.4570              -9.56E+01         2.88      124         2.43                     28
 1.00E+06  6.28E+06     5.5205              -9.28E+01        -2.06      109         3.46                     16



                                      Modulator Gain/Phase
                                        COMP to VOUT


               60                                                                     0

               40                                                                     -30

               20                                                                     -60
                                                                                             Phase (deg)
   Gain (dB)




                0                                                                     -90

               -20                                                                    -120

               -40                                                                    -150

               -60                                                                    -180
                1.E+00   1.E+01   1.E+02       1.E+03       1.E+04     1.E+05     1.E+06
                                           Frequency (Hz)




                                    Error Amplifier Gain/Phase
                                          VOUT to COMP


               100                                                                     180

                80                                                                     150
            60                                                                 120




                                                                                     Phase (deg)
Gain (dB)
            40                                                                 90

            20                                                                 60

             0                                                                 30

            -20                                                                0
             1.E+00   1.E+01   1.E+02       1.E+03       1.E+04   1.E+05   1.E+06
                                        Frequency (Hz)
                                                                                                   Mod RHP
pole at orgin Dominant mod                                    ModESRz                                ZERO
    gain           pole                     ModRHP Zero          ero    error zero error hf pole     Phase
  7.5300E+01    -8.48415E-07                 -7.13517E-10      1.33E-11 8.48E-07       -4.19E-13   -0.000734
  6.9279E+01    -3.39366E-06                 -2.85407E-09      5.30E-11 3.39E-06       -1.67E-12   -0.001469
  6.1321E+01    -2.12103E-05                 -1.78379E-08      3.31E-10 2.12E-05       -1.05E-11   -0.003672
  5.5300E+01    -8.48407E-05                 -7.13517E-08      1.33E-09 8.48E-05       -4.18E-11   -0.007344
  4.9279E+01    -0.000339353                 -2.85407E-07      5.30E-09 3.39E-04       -1.67E-10   -0.014688
  4.1321E+01     -0.00212052                 -1.78379E-06      3.31E-08 2.12E-03       -1.05E-09    -0.03672
  3.5300E+01    -0.008475875                 -7.13517E-06      1.33E-07 8.48E-03       -4.18E-09    -0.07344
  2.9279E+01    -0.033804697                 -2.85406E-05      5.30E-07 3.38E-02       -1.67E-08    -0.14688
  2.1321E+01    -0.207087031                 -0.000178376      3.31E-06 2.07E-01       -1.05E-07   -0.367195
  1.5300E+01     -0.77496828                 -0.000713458      1.33E-05 7.75E-01       -4.18E-07    -0.73436
  9.2793E+00     -2.50766124                 -0.002853131      5.30E-05 2.51E+00       -1.67E-06   -1.468478
  1.3205E+00    -7.696630597                 -0.017801394      3.31E-04 7.70E+00       -1.05E-05   -3.666985
 -4.7001E+00    -13.12504848                 -0.070771921      1.33E-03 1.31E+01       -4.18E-05   -7.304173
 -1.0721E+01    -18.98406571                 -0.276420375      5.30E-03 1.90E+01       -1.67E-04   -14.37837
 -1.8679E+01    -26.89652418                 -1.494449661      3.30E-02 2.69E+01       -1.05E-03    -32.6552
 -2.4700E+01     -32.9104633                 -4.220862895      1.31E-01 3.29E+01     -4.183E-03    -52.03967
 -3.0721E+01    -38.92939641                 -8.791954235      5.00E-01 3.89E+01     -1.671E-02    -68.68996
 -3.8679E+01    -46.88772977                 -16.24007049      2.46E+00 4.69E+01     -1.034E-01    -81.13141
 -4.4700E+01    -52.90826299                 -22.18255468      6.08E+00 5.29E+01     -3.995E-01    -85.53898
 -5.0721E+01    -58.92884623                 -28.18340413      1.12E+01 5.89E+01 -1.416E+00        -87.76611
 -5.8679E+01    -66.88764173                 -36.13665804      1.89E+01 6.69E+01 -5.326E+00        -89.10606
 -6.4700E+01    -72.90824098                 -42.15646505      2.49E+01 7.29E+01 -1.027E+01           -89.553




                              Overall Gain and
                              Phase
          100                                                                   180

               80                                                               150

               60                                                               120
   Gain (dB)




               40                                                               90

               20                                                               60

                0                                                               30

               -20                                                              0
                 1.E+00   1.E+01   1.E+02     1.E+03     1.E+04   1.E+05   1.E+06
                                            Frequency (Hz)
                  MOD
                Dominate
MOD ESR Zero      Pole
  0.000100109   -0.025324
  0.000200218   -0.050648
  0.000500545    -0.12662
  0.001001091    -0.25324
  0.002002181    -0.50647
  0.005005453   -1.266001
  0.010010905   -2.530767
  0.020021809   -5.051697
  0.050054513   -12.46177
  0.100108949   -23.84493
  0.200217288   -41.47601
  0.500532523   -65.65328
   1.00098866   -77.25148
  2.001366648   -83.54586
  4.992776597   -87.40914
  9.910859664   -88.70391
   19.2617896   -89.35187
   41.1409916   -89.74074
  60.21604126   -89.87037
  74.03063503   -89.93518
  83.46996065   -89.97407
  86.72434322   -89.98704