0
\$\begingroup\$

I am implementing a USB-to-system-to-battery charger (TI BQ25730 or TI BQ25723), which:

  • Converts USB voltage 5+ [V] to 4.2 [V] for system and battery, or
  • Provides battery voltage (4.2 [V] down to 2.7 [V]) to system
Part f.sw [MHz]
TI BQ25730 0.4 or 0.8
TI BQ25723 0.8 or 1.2

V.sys (2.7 — 4.2 [V]) gets bussed as V.in to several switching converters (TI TPS63810) with outputs ranging from 2.9 to 3.7 [V].

According to the datasheet:

\$ f.sw \left(@: I_{out} = 1 \left[A\right], V_{out} = 3.3 \left[V\right]\ \right) = 1.2\ to\ 2.5 \left[MHz\right] \$

enter image description here

Thus, the lowest switching frequency on the charger would be the default choice to maximize switching efficiency, but is there any other preferable consideration when selecting a switching frequency for the charger, possibly when considering the switching frequency of the ICs that the charger outputs to?

\$\endgroup\$

1 Answer 1

2
\$\begingroup\$

Higher switching frequencies will result in smaller solution size (smaller inductors, maybe less output capacitance).

Of course as you said the penalty is efficiency. In some cases EMI might be a consideration if there is any circuitry that may be sensitive to the switching frequency or a harmonic of it.

It's also possible (but not a given) that higher switching frequency may result in higher loop bandwidth and better transient response for your system load as well as lower output ripple. (Not so important for the charger loop).

The switching frequency of downstream converters shouldn't normally have a bearing on choosing the charger Fsw.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.