L6924D Battery charger NTC selection

[Levan]

I require assistance with the design of the battery charger schematics involving the L6924D. Referring to the documentation (https://www.st.com/resource/en/datasheet/l6924d.pdf), the pull-up resistor R3 is 1K, and the NTC tuning resistor R9 is 470 ohms. My inquiries are as follows:

1. Should I incorporate the NTC thermistor as depicted in red on the schematics, or is R9 itself an NTC?

2. In section 8.1 of the document regarding the selection of the appropriate NTC, at 0 degrees Celsius, is the resistance NTC||R9 equal to R3, or is R9 equal to R3? Furthermore, at 50 degrees Celsius, is R3(1K)/NTC||R9 equal to 7 or R3/R9 = 7?

[Levan]

In section  8.1- "NTC thermistor", on Fig 21, from TH pin to the ground there is NTC resistor. However, description of R9 resistor for Fig 25 says that its "NTC Tuning Parallel resistor".

[Peter BENSCH · Accepted solution]

There are several ways of connecting an NTC to pin TH: e.g. R4 in Fig. 2 is an NTC without or with an additional parallel resistor. R9 in Fig. 25 places the operating window in a usable range, so to speak. If the NTC is connected to the connector of the same name, the total resistance at pin TH to GND is reduced, but this is not a major problem if R9 is suitably dimensioned.

The NTC supply resistor mentioned in Table 7 (R3 in Fig. 25) refers to the resistor that supplies the NTC branch. The NTC tuning parallel resistor (R9 in Fig. 25) is then the parallel resistor mentioned above, which in this case is connected in parallel with the NTC.

Does it answer your question?

Regards
/Peter