Hi,
The datasheet says,
“The bq24616 has an internal loop compensator. To get good loop stability, the resonant frequency of the output inductor and output capacitor should be designed between 12 kHz and 17 kHz.”
To keep the circuit in the stable region the safest design would perhaps to make the oscillation frequency equals the root(12*17)=14.29KHz.
17/12=141.7%, and its root is 119%.
This means that EVEN if the frequency is 14.29KHz, there cannot be a 119% variation for LC, or it will fall out of stable region, possible leading to runaway behavior.
10% tolerance is practically the lowest for suitable capacitors we have searched, and to meet the range limit the inductor also need to have ≈8.2% tolerance. Combined, we found it has been extremely difficult to find L,C combination simultaneously satisfying both (also meet ripple current/voltage requirement, inductor EMC shielding, etc.).
Please advise us on:
- Any detail on the internal loop compensator? What if due to tolerances the resonant frequency falls out of [12,17]KHz? Would runaways-like behavior happen?
- Granted that we might not be able to find perfect L,C fit, can we use LCR meter in lab to measure and pick those parts whose multiplication is within the range?
Hui