BQ40Z50-R2 datasheet(32/55 Pages) TI2

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must be designed to be as short and wide as possible. Ensure that the voltage ratings of both C1 and C2 are

adequate to hold off the applied voltage if one of the capacitors becomes shorted.

Figure 9-2. BQ40Z50-R2 Protection FETs

9.2.2.1.2 Chemical Fuse

The chemical fuse (Dexerials, Uchihashi, and so on) is ignited under command from either the bq294700

secondary voltage protection IC or from the FUSE pin of the gas gauge. Either of these events applies a positive

voltage to the gate of Q5, shown in Figure 9-3, which then sinks current from the third terminal of the fuse,

causing it to ignite and open permanently.

It is important to carefully review the fuse specifications and match the required ignition current to that available

from the N-channel FET. Ensure that the proper voltage, current, and Rds(on) ratings are used for this device.

The fuse control circuit is discussed in detail in Section 9.2.2.2.5.

to 2

nd Level Protector

to FUSE Pin

Figure 9-3. FUSE Circuit

9.2.2.1.3 Li-Ion Cell Connections

For cell connections, it is important to remember that high current flows through the top and bottom connections;

therefore, the voltage sense leads at these points must be made with a Kelvin connection to avoid any errors

due to a drop in the high-current copper trace. The location marked 4P in Figure 9-4 indicates the Kelvin

connection of the most positive battery node. The connection marked 1N is equally important. The VC5 pin

(a ground reference for cell voltage measurement), which is in the older generation devices, is not in the

BQ40Z50-R2 device. Therefore, the single-point connection at 1N to the low-current ground is needed to avoid

an unwanted voltage drop through long traces while the gas gauge is measuring the bottom cell voltage.

BQ40Z50-R2

SLUSCS4C – JUNE 2017 – REVISED APRIL 2021

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