Texas Instruments’ BQ40Z50 Alternative

Many moons ago, creating a battery for a mobile device was simple. You grabbed a few nickel cadmium cells, trickle charged them and you were sorted. Today, advanced battery chemistry and their explosive behaviour make matters more difficult. Fortunately, TI‘s BQ40Z50 family provides a convenient alternative – and communicates via Intel’s SMBus standard.

The Texas Instruments chip handles primary protection for a battery pack consisting of between one and four Lithium-Ion or Lithium-Polymer cells switched in series. Providing a field effect transistor for charging and discharging is the responsibility of the developer; this is not a chip which works without the presence of a significant amount of additional logic.

Fortunately, TI provides suggestions for a lot of it. For example, the CSD17308Q3 part – conveniently found via OEMsecrets – is ideally suited to handle the charging and discharging of the cells due to its extremely low internal resistance.

Actual cell health is then determined via a group of relatively complex proprietary algorithms, which collect input from, amongst other things, a set of shunt resistors and thermal monitors which are to be embedded into each cell. Another nifty feature involves the SMBus interface mentioned in the introduction. This provides a simple way for the host processor to find out more about the current status of the battery. In systems which are based on an Intel microprocessor, this information can be used to enable or disable the overclocking feature of the CPU.

These features are rounded off with an SHA1 based authentication module and a set of flash based memories which stores lifetime information about the batteries performance and behaviour. This is especially useful for rejecting cloned batteries, and can also be used to reject warranty claims due to improper handling of the cells at hand.

A tale of two versions

Logic dictates that fitting all of this functionality into a 32 pin case requires some kind of compromise. In the case of the BQ40Z50, developers need to live with two problems. The above-mentioned need for a significant amount of external circuitry and the configuration, which takes place entirely using software. TI provides a programming utility called bqSTUDIO, which is furthermore described in a dedicated data sheet available here.

Finally, keep in mind that two versions of the chip exist; the deprecated BQ40Z50, and its successor BQ40Z50-R1. A quick comparison of the datasheets provided by the OEMSecrets team yielded no significant differences on the semiconductor side – the differences are likely to be found on the firmware side of things.

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