NR421A Calculation Tool

Before Using This Tool

  1. This tool is designed to help you calculate Peripheral Circuit Constants, Design Values and Power Losses in a NR421A DC/DC Converter system.
  2. Before using this tool, please read the NR421A data sheet.
  3. All the device characteristic parameters are typical values at TJ = 25 ℃
  4. All the values automatically entered into the text boxes in the Calculation Conditions pane are default values (for reference).
  5. All the values calculated by this tool are reference values, NOT guaranteed values.
  6. This tool has NOT been guaranteed to work properly on all browsers.

Runing a Calculation

  1. In the Calculation Conditions pane, move the slider to set a numerical value in each field.
    2. − Move the slider to enter or adjust a numerical value in each text box.
    − To enter a numecial value directly, click or tap (hereafter “click”) in the field.
    − When using a keyboard, click to select the slider thumb, and then use arrow keys (left and right) on your keyboard to move the slider.
  2. To run a calculation, click the Calculate button.
    3. − To run a new calculation after you made any changes to the values entered, click the Calculate button again.
    − If the tool displays an error calculation result after you click the Calculate button, see “Troubleshooting” below.

Reset Button

  1. Resets all the values entered in the Calculation Conditions pane.
  2. Resets all the positions of the slider thumbs in the Calculation Conditions pane to their default settings.
  3. Makes no change to the values in the Calculation Results pane.

Troubleshooting

  1. SYMPTOM: " NaN " is displayed in the Calculation Results pane.
    2. − Either one or more fields in the Calculation Conditions pane are left blank.
    − Any of the user-entered values contains numerals or characters other than half-width digits or a half-width period ( . ).
    − Any of the user-entered values contains a half-width period ( . ) at an invalid position.
    Examples: “ .3.4 ”, “ .2. ”, “ 0.6. ”

The Basics Explained

Basic Circuit Connection



Description of circuit symbols in Basic Circuit Connection


  • CIN ： Input Smoothing Capacitor
  • COUT ： Output Smoothing Capacitor
  • CSS ： Soft-Start Timing Capacitor
  • CBS ： Power Supply Capacitor for High Side Driver ( Default Value : 0.1µF )
  • REN1 ： Enable Terminal Setting Resistor ( Default Value : 100kΩ )
  • RFB1 ： Output Voltage Seinsing Resistor ( For Voltage Divider / Upper)
  • RFB2 ： Output Voltage Seinsing Resistor ( For Voltage Divider / Lower)
  • IFB ： Feedback Current Value that is flowing RFB1 to RFB2
  • Inductor : Inductance L Value


Inductance L Value Calculation Procedure


  1. Enter the wished inductor ripple current ⊿IL value into the text box of ⊿IL setting .
  2. Click the Calculate button and calculate inductance L value.
  3. Please refer to the inductor manufacturer's catalog and select parts with close values.
  4. Enter the selected inductance L value into the text box of Inductance L Value Setting.
  5. Click the Calculate Button and recalculate ⊿IL according to the selected inductance L value.

Setting Criterion of Inductor Ripple Current ⊿IL


VIN(V) VO(V) Duty D ⊿IL (A) Conditions
18 14 0.78 ⊿IL≦0.494
18 12 0.67 ⊿IL≦0.740
18 10 0.56 ⊿IL≦0.988
15 12 0.80 ⊿IL≦0.446
12 9 0.75 ⊿IL≦0.554
10 7 0.70 ⊿IL≦0.667
9 6 0.67 ⊿IL≦0.740
9 5 0.56 ⊿IL≦0.988
8 5 0.63 ⊿IL≦0.832
- - D<0.5 0.4≦⊿IL≦0.6

Supplementary matter


  1. The entered target efficiency η value is used to estimate the input current Iin approximatly. It is necessary when you estimate the load current of the transformer secondary winding.
  2. Regarding the setting of the target output ripple voltage, please enter the value how do you want to suppress the output ripple voltage magnitude ? (Unit : mV peak to peak)
  3. It is recommended that the entering value of feedback current IFB setting be 200 μA or more.
  4. When priority is given to the RFB2 resistance value between FB and GND, RFB1 resistance value is inverse calculated.
  5. The Resistance values of RFB1 and RFB2 do not perfectly match the geometric series such as E12 series, E24 series etc. Adjust the Resistance value by multiple combined resistors with series connection or parallel connection.
  6. In the calculation result, the ESR requirement value and ripple current of the output smoothing capacitor COUT are calculated by the user selected inductance L value.
  7. The internal loss of NR421A must be within the thermal derating curve ( Ambient Temperature vs. Power Dissipation characteristic ) shown in the data sheet.




Calculation Conditions


4.5 18
0.8 14
0 3.0
0 Fixed Value
50 99
0.1 1.0
1 1000
1 140
0.001 1
200 1200
0.62 3.90

■ Calculation Results

Output Power PO:

---

W

On-Duty D:

---

Switching Cycle T:

---

µs

Ton:

---

µs

Toff:

---

µs

Input Current Iin:

---

A

Soft-Start Time tSS:

---

ms

Delay Time t_delay:

---

ms

Start-up Time:

---

ms

Discharge Time to VSS1:

---

ms

Inductance L Value by user decided ⊿IL condition:

---

µH

⊿IL Value by user decided Inductance L Value:

---

A

ESR Required Value of Output Smoothing Capacitor COUT:

---

mΩ or less

Output Smoothing Capacitor COUT Ripple Current:

---

Arms

Input Smoothing Capacitor CIN Approximate Ripple Current:

---

Arms

Power Dissipation in Control Circuit PD1:

---

W

Switching Loss in Power MOSFET part PD2:

---

W

Total Loss PD (PD1 + PD2):

---

W

Output Voltage Sensing Resistor RFB1:

---

kΩ

Output Voltage Sensing Resistor RFB2:

---

kΩ

When the RFB2 Resistance Value is priority, Output Voltage Sensing Resistor RFB1:

---

kΩ

When the RFB2 Resistance Value is priority, Feedback Current IFB:

---

µA

Total loss PD exceeds the absolute maximum rating of 2.97 (W). Since the loss is too large, the usage conditions need to be reviewed.

DT0023: NR421A Calculation Tool Rev.2.0