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TPS62140A: About Soft Start Capacitor calculation formula

Part Number: TPS62140A
Other Parts Discussed in Thread: TPS62135

Hi,

Could you tell me about soft start cap calculation formula.



What is this voltage (1.25V)?
There was no description in the Electrical Characteristics of the data sheet.
Therefore, I got a question from the customer.
Also, the customer wants to know the maximum value and the minimum value in order to consider the soft start time.

Best Regards,
Yusuke/Japan Disty

  • The 1.25V is explained in the very next section and shown in Figure 8. There is a gain between the SS/TR pin and FB pin. SS/TR should be above ~1.25V for FB to be at its full 0.8V level. Ideally, the 1.25V should be 1.2V as shown in Figure 8, but due to non-linearities at the end of SS, 1.25V should be achieved for a full 0.8V at FB.

    The tolerance on the 1.25V value can be neglected, compared to the ~10% tolerance of the SS cap and the tolerance of the SS/TR current source itself (also about 10%).

    As well, the TPS62135/6 offer a smaller size, higher current, and better accuracy and can be recommended.