• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 395 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ24125: 3 Cell battery charging issue

BQ24125: Calculating Riset2

Derek
Mastermind 9792 points
Part Number: BQ24125

Hello,

   The calculations for Riset2 (equation 18 on page 24 of bq24125 datasheet) state that:

Kiset2 = 1000 (confirmed in datasheet)

Rsns = from my schematic, e.g. 0.5 ohms in my case

Icharge = the fast charge current correct? In our case it would be 200mA.

Where is Viset2 defined? Datasheet mentions 100mV (Precharge set voltage, ISET2, on page 6) BUT, the example in the datasheet (again, equation 18) uses 1.0.

For this board, Riset1 = (Kiset1 * Viset1 ) / (Rsns * Icharge) = (1000 * 1) / (0.5 * 0.2) = 10k

I have the board running, and have verified that I'm getting 0.2A with the 10k Riset1 value.

But I don't have a way of verifying Riset2 without waiting for the whole charge cycle to complete, and that's like watching paint dry.

  • 0
    TI__Guru**** 166826 points
    Hi Derek,

    Viset2 is 0.1V +/-20% per datasheet page 6. Equation 18 has two typos, where Viset2 should be 0.1V and ICHARGE should be either IPRECHARGE= ITERM=0.133A. Essentially Viset2 is 10% of Viset1 so if you use the same sized resistor for Rset1 and Rset2, the precharge and termination currents will be 1/10 of the fast charge current.